Basics Roof Construction 9783035619584

Citation preview

Ann-Christin Siegemund

Roof Construction

Ann-Christin Bert BielefeldSiegemund - Sebastian El Khouli

Entwurfsidee Roof Construction Third edition

Birkhäuser BIRKHÄUSER Basel BASEL

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Contents FOREWORD _7 INTRODUCTION _8 BASICS AND DESIGN FACTORS _9 Forces and types of load _9 Building physics _11 Fire safety _14 Lightning protection _15 Materials used _16 Planning and building codes _18

SLOPING ROOFS _19 Roof styles _20 Dormer and roof windows _22

ROOF CONSTRUCTION _26 Woodworking joints _26 Closed couple roof _28 Collar beam roof _30 Purlin roof _31 Solid roof _34

ROOF CONSTRUCTION LAYERS _36 Types of roof covering _36 Roof battens _39 Roofing membranes _40 Insulation _41 Drainage details _44

FLAT ROOFS _46 Construction _46 Types of roof construction _47 Connection details _48 Edge details _49 Roof layers _52 Green roofs _55 Drainage details _56

ADDITIONAL COMPONENTS _59 Fall prevention on roofs _59 Photovoltaics and solar collector systems _63

IN CONCLUSION _65 APPENDIX _67 Literature _67 Standards _68 Picture Credits _72 The Author _72

Foreword To have a roof over your head is one of the basic needs of human existence – it protects us from rain and wind, and helps us to keep warm. To do that, the roof also needs to fulfill some other functions: it needs to be structurally sound and stable. Based on traditional craftsmanship, various types and styles of roofs have evolved, which fulfill these functions in different ways and which are still in use today. In addition, the roof – which is often referred to as the fifth facade – is also considered under aesthetic aspects. Versions of flat and sloping roofs have a significant impact on the appearance of historical towns and villages, and in modern buildings, too, they are an important part of the conceptual design. Thus, the fifth facade of a building with its many facets – comprehensively covered in this volume – is a key element in the architectural and structural design of a building. This volume, Basics Roof Construction, is intended for the student who, for the first time, is considering the aspects involved in the design of a roof. The book introduces the various types of roof, their advantages and disadvantages, and the construction details the designer needs to be familiar with. In a clear and straightforward way, all the structural and non-structural aspects are explained, including the key design criteria. The student is given comprehensive information – from the basic structure of the roof to the insulation, waterproofing, finishes, surfaces, and drainage systems. The aim of the book is to provide students with an understanding of the principles, the technical terms, and the types and styles of roofs, and their characteristics, to enable them to produce roof designs that meet all the relevant criteria. This is the second edition of the book, which has been comprehensively revised in structure and content. The author starts with a description of the general requirements a roof has to fulfill and then explains the key characteristics of sloping roofs and flat roofs. This is followed by the thoroughly updated chapters on the various roof construction aspects, ending with detailed explanations of photovoltaics systems and solar collectors, as well as on the design of green roofs, both of which have become standard elements of roof design for reasons of climate protection. Bert Bielefeld, Editor

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Introduction The roof is part of the envelope of a building and has a number of different functions, which are performed by different parts of the roof. Whether it is open or fully enclosed, the space beneath the roof is protected against wind, rain, and direct sunlight by the roof covering in combination with the underslating/waterproofing membrane. A layer of ­insulation ensures that both heat losses and heat gains are reduced. The roof envelope is supported by the structural members of the roof construction, the function of which is to transfer the loads impacting on the roof from the outside as well as those resulting from its own construction into the ground via external walls, pillars, and foundations. Furthermore, there are secondary elements that are needed to ensure that the main functions of the roof can be fulfilled. In addition to the protective functions, aesthetic aspects such as the overall form, construction, finishes, and detailing also need to be taken into consideration. Taking into account current concerns about climate change, roofs may also be designed with “greening” in order to compensate for the ground area that is covered by the building. However, the selection of individual components should always take into account the respective construction task in hand. For example, elaborate prefabricated steel structures are rarely found in private housing projects; similarly, in industrial building, one generally tries to avoid details that require extensive craftsmanship on the building site. The shape of roofs is primarily determined by design considerations relating to the respective building and planning aspects but may also reflect regional differences. In Alpine regions, shallow sloping roofs with a large roof overhang are most common, whereas in the northern coastal regions of Europe, gable roofs with steep slopes are more usual. > Chapter Roof styles Different building functions have also led to typical roof styles: for example, tennis halls often have curved barrel roofs that allow space for the trajectory of the tennis ball; by contrast, normal congregation spaces often feature flat roofs to enable a flexible range of uses. It is also possible to combine different styles of roof. A basic distinction is made between sloping roofs and flat roofs, with sloping roofs generally considered to have a minimum slope of 5°. In view of the fact that these two roof styles differ significantly in construction and function, they are dealt with in separate sections of this book, following the description of some basics.

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Basics and design factors Apart from the pure conceptual design, a number of factors have to be considered, which affect the shape of the roof, the materials of the different layers, as well as additional elements. Below we will briefly ­explain the main criteria of factors such as structure, building code, building physics, fire safety, and building material properties in order to ­establish how these design elements fit together in the construction methods described below. FORCES AND TYPES OF LOAD

The structure of a building is designed to ensure its structural integrity, which means that forces are balanced and building components do not move. This means that any impacting forces must be countered with forces that are at least of equal strength. In addition, internal forces must also be balanced. This means that building components must be capable of withstanding all internal and external forces, which in turn depends on their sizing, strength, and the elasticity of the material. When a building component is exposed to compression, it has to resist compressive forces. Conversely, when the forces acting on a building component tend to pull it apart, it has to resist tensile forces. A building component exposed to counteracting forces impacting at different points will be subjected to torsion. As a rule, the term used in building construction to describe this is “moment” or “moment of force”. The sum of all impacting forces is the force (also bearing force) that is transferred to the construction element below, which must be capable of resisting it. Buildings are subject to a number of different forces, the size of which must be established as part of the structural design. The forces acting on a building or a building component are also referred to in terms of the direction of impact – a distinction is made between longitudinal forces and transverse or shear forces. Loads may impact horizontally (both transversally and longitudinally) and also vertically. > Fig. 1

Compression

Tension

Moment

Fig. 1: Forces

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Compressive and tensile force, moment

Types of load in a roof structure

◼

A basic requirement for the structural design of a roof is the computation of the various loads. At this stage, the structural engineer will decide what materials will be used. On this basis the self-weight (also called dead load) of the construction can be calculated. The self-weight is a permanent load. Its impact is vertically downwards. In addition, there is the imposed load (also called live load). Typical examples are movable objects, such as furniture, or people. It is, however, not necessary to account for each individual item in the structural design. Instead, it is possible to use average values that have been established for various types of buildings, such as apartments, warehouses, or factories. Where no ­imposed load is expected on a building component, e.g., a sloping roof surface, it is nevertheless necessary to provide proof that the building component can support a person or persons during construction and for the purpose of maintenance. As a rule, the impact of imposed loads is vertically downwards like that of dead loads.

Table 1: Types of load Type of load

Duration

Main direction

Calculation

Dead load

permanent

vertical

The load is calculated using the quantity and specific ­gravity of the components (in KN/sqm).

Live load

variable

vertical

Average values for specific functions are available from tables (in KN/sqm).

Snow and ice load

variable

vertical

Figures are available in tables for different roof slopes and snow load zones.

Wind load (wind pressure)

variable

perpendicular to the roof surface

Figures are available in tables for different roof slopes and wind load zones.

Wind load (wind suction)

variable

perpendicular to the roof surface

Figures are available in tables for different roof slopes, building heights, and orientation.

◼ Tip: Different states/countries maintain standard tables, where the various weights of materials and building components, as well as assumptions as to imposed loads, snow and wind loads, can be found in order to calculate the total load. A list of the most important standards is included at the end of this book. For further details on the subject of structural systems, see Basics Loadbearing Systems by Alfred Meistermann. GSPublisherVersion 70.85.88.100

GSPublisherVersion 70.85.88.100

GSPublisherVersion 70.85.88.100

GSPublisherVersion 70.85.88.100 GSPublisherVersion 70.85.88.100

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Other forces to be considered are environmental loads, such as wind, snow, and ice acting on the roof. Whereas snow and ice add weight to be supported by the roof, resulting in vertical loads, wind may impact both horizontally and vertically. Wind can cause pressure as well as suction. Wind suction is a force that tends to lift off building components. Any components exposed to wind suction must be secured with appropriate means. > Fig. 2 BUILDING PHYSICS

Roofs must fulfill all essential functions defined by building physics in terms of thermal and sound insulation, as well as protection against moisture ingress and fire > Chapter Fire safety. In view of the fact that building physics influences the way roofs are designed and constructed, we discuss the most important aspects below. Where buildings are fitted with good thermal insulation, e.g., by insulating building components exposed to the exterior, it is possible to significantly reduce the consumption of energy for heating or cooling. In this case it is not only important to insulate the primary parts of the structure, but also consider the transition details between different building elements since these can cause thermal bridging. In heated buildings, roof structures are fitted with layers of insulation; these have low thermal conductivity and thereby provide thermal insulation to the building. Thermal conductivity is the specific value of a material relating to the energy that flows every second through a cube of material with an edge length of 1 m when the temperature differential

◯ Note: Thermal protection is not only relevant in

­ inter, but also during the summer months. During w summer, thermal protection reduces solar heat irradiating the building, which in turn reduces the amount of energy needed to cool the building. Typical devices include external solar shading blinds in front of windows. In winter, thermal protection/insulation reduces heat loss from buildings, which means that less energy is required for heating. The amount of heat lost from a building is affected by the ratio of external building surface to the heated volume inside the building, by the degree to which building components are insulated on the external face, by the air tightness of the building, and by the presence of thermal bridges.

◯

Thermal bridges

◯

Thermal conductivity

◯ Note: Thermal bridges in building construction occur where the insulation layer of a building is interrupted or reduced in thickness. When there is a significant difference between the outside and inside temperature of a building, this can lead to heat loss during the winter months and heat gain in summer.

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between the two external faces is 1 Kelvin. The lower the thermal conductivity of a material, the higher its insulating effect. Dividing the thickness of a material by its thermal conductivity reveals the thermal resistance (R) of the respective layer of material. Adding the thermal resistance of all layers together, as well as the heat transfer resistance of the outer and inner surfaces of the building component results in the heat transfer resistance of the building component. The greater the heat transfer resistance of the component, the better its thermal insulating effect.

Table 2: Nominal and design values of the thermal conductivity of selected materials as per DIN 4108 and DIN EN ISO 10456 Material

Thermal conductivity, nominal value [W/mK]

Thermal conductivity, design value [W/mK]

Mineral wool insulation

0.03–0.050

0.036–0.06

EPS

0.03–0.050

0.036–0.06

XPS

0.026–0.045

0.031–0.054

Polyurethane

0.02–0.040

0.024–0.048

Rigid phenolic foam

0.02–0.035

0.024–0.042

Steel-reinforced concrete

–

2.3

Construction steel

–

approx. 50

Construction timber

–

0.13

Table 3: Example calculation of the U-value of a flat roof Construction of a flat roof from interior to exterior

Material thickness d [m]

Thermal conductivity

Formula: R=d/

Thermal resistance R [m²K/W]

Thermal transition, interior (RSI)

–

–

–

0.1

Plaster Reinforced concrete structural ceiling

0.015

0.51

0.015/0.51

0.029

0.25

2.3

0.25/2.3

0.11

Bitumen membrane

0.003

0.23

0.003/0.23

0.013

Insulation

0.28

0.035

0.28/0.035

8.00

Plastic sealing layer with ­separating membrane

0.005

0.17

0.005/0.17

0.029

Thermal transition, exterior (RSE)

–

–

–

0.04

[W/mK]

Thermal resistance RT=∑R Thermal transmission coefficient U=1/RT

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8.321 m²K/W 0.12 W/m²K

It is important to prevent condensation on the surface of building components as well as in the various layers. The occurrence of condensation depends on the temperature and relative humidity. In winter, air diffusing through the layers of material from the inside to the outside will cool down. Warm air can absorb more moisture than cold air; when warm air cools down, it can no longer hold the excess moisture, which will therefore condense and lead to condensation. If this condensate cannot escape, the moisture can impair the function of the roof and also lead to the formation of mould on surfaces. In certain situations, roofs are also required to provide a degree of sound insulation, partly to limit the impact of any noise from the outside and partly to attenuate noise from inside the building. Sound is transmitted either as airborne sound or as impact sound, or as a combination of the two. For roofs as exterior building components, the main concern is insulation against airborne sound. Nevertheless, additional measures may be required when noisy technical equipment, such as air-conditioning units, is placed on the roof and the rooms beneath need to be protected. In single-skin roofs, i.e., roof structures without an air layer, the sound insulation is normally good due to the greater weight per area. In multilayer constructions it is important to ensure that all layers have an adequate weight per area and that the insulation has good sound-­ absorption properties.

◼ Tip: In some configurations it is possible that the spread of sound is even augmented in multilayer constructions. For this reason, such a construction should always be checked/tested for its sound insulation effect. See also Basics Sound Insulation by Dominic Kampshoff.

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Prevention of condensation

Sound insulation

◼

FIRE SAFETY

Normally, roofs also have to satisfy fire safety requirements. Fire protection in buildings is primarily aimed at the following: —— —— —— ——

Fire behaviour and period of fire resistance

◼

Hard roof covering ◯

Classification as per EN 13501

Preventing a fire from starting Preventing a fire from spreading Facilitating the rescue of people at risk from a fire Facilitating effective extinguishing work

Building materials react differently to heat and fire; with an appropriate combination of materials in the construction, it is therefore possible to ensure that fire cannot spread through the building components and that the structural integrity of the building is retained for a certain period. Even though steel components do not burn, they do heat up much quicker than timber and will deform when exposed to even small increases in ­temperature – which can lead to the loss of the structural loadbearing ­capacity. By contrast, even though timber is classed as a combustible material, its behaviour when exposed to fire is much better because it will sustain its loadbearing capacity for a certain period of time even when its outer layer is already charred. When assessing building materials from the point of view of fire safety, a primary distinction is made between the fire behaviour and the period of fire resistance. The fire behaviour describes the extent to which a material is combustible and how quickly it can be ignited. The period of fire resistance specifies the period during which the material retains its protective effect and/or its structural capacity when exposed to fire. The term “hard roof covering” is used to refer to roof covering that is resistant to the spread of fire by wind and to radiant heat. A hard roof covering provides protection against being ignited by flying sparks and radiant heat; examples are a min. 5 cm-thick layer of gravel or metal sheeting with a thickness of at least 0.5 mm. European standard EN 13501 classifies the behaviour of building materials in the case of fire using building material classes A to F. In addition, factors such as the development of smoke – “s” for smoke, graded from s1 to s3 – and burning material droplets – “d” for droplets, graded d0 to d2 – are taken into account. The subdivision of the period of fire resistance is made along a scale from 15 to 240 minutes.

◼ Tip: For fire safety requirements and details, see Basics Fire Safety by Diana Helmerking.

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◯ Note: The term “roof covering” only refers to the skin of the roof, i.e., the covering material, the waterproofing, and the insulation. The term “roof” refers to the entire roof structure, including its loadbearing structure.

Table 4: Building material classes as per DIN 4102-1, Table 1, and DIN EN 13501 Building material class to DIN 4102

Official denomination

Allocation as per DIN EN 13051

Additional requirement no smoke

no burning ­ roplets d

A1

non-combustible

A1

x

x

A2

non-combustible

A 2 – s1, d0

x

x

B1

hardly flammable

B – s1, d0 C – s1, d0 A2 – s2, d0 A2 – s3, d0 B – s2, d0 B – s3, d0 C – s2, d0 C – s3, d0 A2 – s1, d1 A2 – s1, d2 B – s1, d1 B – s1, d2 C – s1, d1 C – s1, d2 A2 – s3, d2 B – s3, d2 C – d3, d2

x x x x x x x x

x x x x x x x x

B2

normally flammable

D – s1, d0 D – s2, d0 D – s3, d0 E D – s1, d1 D – s2, d1 D – s3, d1 D – s1, d2 D – s2, d2 D – s3, d2 E – d2

B3

easily flammable

F

x x x x

Fire safety is also an important consideration in the design of openings in roof surfaces; for example, an adequate distance must be maintained from such openings to neighbouring buildings and/or fire walls. ­Alternatively, the area above the fire walls can be finished with fire-­ resistant cladding of a specified width. LIGHTNING PROTECTION

A lightning conductor fitted to the outside of a building is used to conduct the electric current of a direct or indirect lightning strike into the ground in order to neutralize the energy of the lightning strike and to protect the building and its inhabitants and objects. The elements of

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Fig. 2: Lightning conductor fitted to an evaporation cooler on a flat roof

Fig. 3: Lightning conductors on a flat roof

the lightning protection system consist of highly conductive material, such as steel or copper. Lightning conductor systems consist of meshes spread across the roof surface, with additional conductor points at elevated places such as the ridge or chimneys. Depending on requirements it may also be necessary to include aerials, gutters/downpipes, flashing, and so on, in the system.

MATERIALS USED

Mineral insulation materials

Depending on the type of roof design, the construction of layers, and the specific functions, materials may have to comply with additional requirements relating to compressive strength, combustibility, or method of installation. For this reason, a range of different materials are used for covering, insulating, and constructing roofs, as well as for roofing membranes. > Chapter Roof structures and Chapter Roof construction Below is a brief introduction to roofing membranes that can be used in flat roofs as well as sloping roofs. Inorganic/mineral insulation materials such as glass wool and rock wool are often used in sloping and flat roofs in the form of rolls or bats. In addition, insulation can also be placed in loose form, either blown in or laid as loose wool. In flat roofs the insulation may consist of mineral insulation slabs or foam glass products. All these products have the advantage of being non-combustible. Glass and mineral wool insulation bats also have hydrophobic properties, which means – some-

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times due to additional treatment – that they repel water and do not lose their ­insulating properties once any moisture that has penetrated has dried out. Organic insulation materials used in roofs, i.e., insulation consisting of renewable natural materials, are usually based on timber, hemp, or flax fibres. As a rule, these are combustible and are available in rolls, bats, or in loose form. Compared to other insulating materials, they have the advantage of a good diffusion value but also the disadvantage of better thermal conductivity and hence poorer thermal insulation, which means that thicker layers of the material have to be applied. Synthetic insulation materials, i.e., rigid foam plastics, are typically used in the form of expanded polystyrene (EPS), extruded polystyrene (XPS), rigid polyurethane foam, or polyisocyanurate foam (PIR). In contrast to mineral insulation materials, plastic foam materials are flammable. In the case of a fire, these insulation materials tend to produce a lot of smoke gases, many of which are toxic. On the positive side, these materials have high compressive strength, low weight and – compared to mineral insulation materials of the same thickness – better insulation properties. The majority of damp-proofing systems are based on bitumen or plastic membranes. However, it is also possible to use damp-proofing liquids, either based on plastic or on bitumen, or a combination of membranes and liquids, which may be advantageous in certain situations. Bitumen and polymer bitumen membranes are produced from crude oil; in polymer bitumen membranes, other materials are added, such as polypropylene, which ensure that the membranes remain flexible even at low temperatures. The membranes are reinforced by adding glass or plastic fibre mesh and can be further enhanced by adding ­granulate on the surface or by laminating foil as a separating layer on the underside, depending on the respective requirements. This means that there are membranes for various functions, for example, ­underslating, ­a vapour barrier, a damp-proofing membrane as the finishing layer on a roof, through to root-protection membranes in green roof construction. Likewise, bitumen membranes can be applied using a range of ­different methods, such as welding, cold self-adhesion, or mechanical fixing. In addition, it is possible to bond bitumen membranes to the roof using a pouring process. Likewise, a large range of plastic membranes is available to suit various applications. However, the basic membrane usually consists of poly­ vinylchloride (PVC), flexible polyolefin (FPO), or polyisobutylene (PIB). Elastomer membranes are produced on the basis of EPDM. Similar to bitumen membranes, they are enhanced with additional layers and may even be combined with bitumen membranes. The membranes are placed loosely and, if necessary, welded at the seams; alternatively, they may also be partly or fully bonded to the substrate.

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Organic insulation materials

Synthetic insulation materials

Damp-proofing systems

In roof construction these membranes are used in combination with other layers such as glass fibre fleeces, plastic fibre fleeces, PE membranes, bitumen membranes, or PVC membranes. The purpose of these additional layers is to separate two materials that are incompatible in the construction (separating layer), to avoid chemical reactions, e.g., between plastic membranes that contain plasticizer and XPS insulating boards, and also in order to protect the damp-proofing system against mechanical impact (protection layer). The construction of green roofs in particular involves products that fulfill functions in addition to protection, such as water storage. PLANNING AND BUILDING CODES

Zoning and land use maps

Building codes

Construction standards

Planning and building codes may determine the style of roof as well as the selection of materials and the roof design. Cities and municipalities usually produce zoning and land use maps (also called local development plans) that determine what buildings can be built in certain areas and may also specify the style of roof. Details may include the shape of the roof, the slope or orientation of the ridge, as well as the maximum height of eaves and/or ridges. In most cases the design will have to take the buildings in the neighbourhood into consideration, which will affect the choice of roofing material and its colour. In many countries the building codes contain significant regulations relating to fire safety. These regulations cover various aspects affecting the fire safety of building components; in northern countries, these codes may include stipulations for safety measures to prevent snow and ice falling from the roof. In addition to the requirements under the building codes, building materials and design details may have to comply with construction standards (see list of standards in the appendix) and the regulations issued by various professional associations.

Table 5: German development plan abbreviations Roof types

Construction height/slope

SD – double-pitch roof

TH – eaves height

PD – monopitch roof

FH – ridge height

WD – hipped roof

OK – top edge

FD – flat roof

WH – wall height

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Sloping roofs In single-family dwellings, most roofs are designed as sloping roofs. Sloping roofs are ideally suited to discharging precipitation that falls on the building. The loadbearing structure of these roofs usually consists of timber and is erected by builders on site. But roof structures made of steel or concrete are also possible. > Chapter Solid roofs The triangular cross-section created by the sloping roof planes is ideal for absorbing wind forces and transferring them to the structure. The highest point of the roof is called ridge and the lower edge is called eaves. The junction between the roof surface and the gable wall of the house is called verge. > Fig. 4 Where two sloping roof planes intersect, the outer intersection line is called hip ridge and the inner one is called valley. When the attic space beneath the roof is to be increased in height, the perimeter walls can be raised by about half a storey height or less (raised part of perimeter wall). The slope of the roof is described by the angle between the sloping roof members and the horizontal members, and is always measured in degrees. By contrast, the term fall is used when referring to the slight incline of items such as gutters or horizontal surfaces that allow precipitation water to drain off. This can be stated in per cent or as a ratio; for example, the typical fall of a flat roof is about 1:40, which is the same as 2.5%. 1 6 2 9

4 2

8

9

45,00°

1 1

5 3 7 6 2

7 3 2 5

8 9

1. First ridge 2. Eaves 3. Valley

4. Roof slope 5. Hip ridge 6. Gable

7. Verge 8. Floor slab 9. Raised part of perimeter wall

Fig. 4: Terms

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ROOF STYLES

Monopitch and double-pitch roof

Mansard roof

Tent roof and hipped roof

Curved roof styles

The different styles of roof are distinguished by the slope of the roof planes and the form of the gable. > Figs. 5 and 6 A roof sloping in one direction only is called a monopitch roof (also shed roof). In some designs two monopitch roofs meet along the same wall but at different levels. The most common style of sloping roof is probably the double-pitch roof (also called gable roof), in which two roof planes that slope in opposite directions meet at the same level: the shared ridge. The position of the ridge line in relation to the floor plan can be from front to back or from side to side. A mansard roof is a roof in which there are two different pitches in the roof plane. The steeper pitch in the lower part of the roof helps to create extra usable space with full headroom in the attic floor. In order to provide even more space inside the attic floor, close to the edge of the roof, it is possible to raise the perimeter wall along the eaves side of the building and thereby raise the roof in its entirety. Traditionally, this raised part of the perimeter wall is about knee-high, hence the German term “Kniestock” (knee wall). Roofs that have a mansard-type construction on two sides only and vertical gable walls on the two other sides are called gambrel roofs. Buildings with gambrel roofs and gable roofs can be placed with the gables facing the street, i.e., the ridge running back to front, or facing the sides. There are also other styles of roof in which the gable walls are fully or partially replaced by sloping roof planes. A roof in which all sloping roof planes over a square building converge at one point at the top is called a tent roof. In a hipped roof, the gable ends are truncated and thus have their own sloping roof planes, which means that the eaves are at the same level on all sides of the building. A roof in which the gable ends feature partly a vertical wall and partly a roof slope, with the eaves at a higher level, is called a half-hipped roof. It is also possible to combine various styles of roof in order to design a suitable roof for a given building. There are also roofs with curved surfaces, which are referred to as vaulted roofs; an example is a barrel roof, which is a roof with a semi-­ circular cross-section. Barrel roofs also have gables at the two ends. Other roof styles with curved surfaces are groin or cross vaults, and domes.

Fig. 5: Double-pitch roof – Mansard roof – Tent roof – Half-hipped roof

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A saw-tooth roof consists of a series of monopitch or double-pitch roofs with a steeper and a shallower side. The steeper side is usually fitted with fenestration. Saw-tooth roofs are often used to cover large buildings such as production facilities.

Double-pitch roof

Gambrel roof

Monopitch roof

Saw-tooth roof

◯

Barrel roof

Roofs with gables

Hipped roof and mansard roof

Half-hipped roofs

Tent roofs

Saw-tooth roof

Fig. 6: Roof styles

◯ Note: The height of habitable rooms in the attic is r­ elevant for the calculation of the usable and habitable floor area in a building. When calculating the usable floor area in accordance with DIN 277, the entire floor area of a usable floor is taken into account. Where the habitable floor area is calculated for the purpose of renting (in Germany this is governed by the Habitable Floor Area Ordinance [WoFlV]), the habitable areas in a loft that are less than 1 m high are not included; half of the areas between 1 m and 2 m high are included; and the areas with a height of at least 2 m are fully included.

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DORMER AND ROOF WINDOWS

Admission of daylight

Trimmers

Dormer styles

Dormer and roof windows are windows in the roof plane that allow daylight to enter the attic floor and, in the case of dormer windows, create extra space and headroom; they may also be inserted for aesthetic reasons. The minimum clear height on the inside of a dormer should be 2 m to allow for sufficient headroom. Where roof windows or dormers are used as a secondary escape route, they are subject to minimum requirements regarding size and sill height. Roof windows are inserted in the roof plane to allow for the admission of daylight and ventilation – prerequisites for using the attic as habitable space. As a rule, the proportion of window area must be one-eighth of the square area of the room. Where the attic is not used as habitable space, it is nevertheless desirable to provide at least a small amount of daylight, for example, by inserting roof hatches. The width of elements fitted in the roof plane should take the roof construction into consideration – in particular the width between the rafters. > Chapter Closed couple roof In order to absorb the loads supported by those rafters that are removed in order to accommodate the roof window, trimmers and trimmer rafters are required. > Figs. 7 and 21 Trimmers are horizontal timber sections that span several fields between rafters, thus supporting the rafters that have been cut off (trimmed) to make the opening; the ends of the trimmers are supported by trimmer rafters. The height of the trimmers and the trimmer rafters should preferably be the same as that of the common rafters in order to ensure that there is no difference in level. Like roofs, dormers can be designed in a number of different styles. > Figs. 8–11 Both the structure and construction layers are subject to the same requirements regarding thermal insulation, sound insulation, and waterproofing as roofs. Likewise, the minimum requirements regarding the angle of pitch also apply. In shed dormers, also called monopitch dormers, the dormer roof has a shallower pitch compared to that of the main roof. Like in a ­gabled

Fig. 7: Roof window with trimmer and trimmer rafter

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­ ormer, the triangular vertical side walls of the dormer are called cheeks. d In gabled dormers the roof is formed like a small, independent double-­ pitch roof fitted into the main roof plane. The joint lines between the dormer roof and the main roof are called valleys. Where the external wall is extended upwards to meet the dormer window, this is referred to as a wall dormer. Dog-house dormers have a double-pitch roof that forms a gable but no vertical sides (cheeks); the dormer roof planes form valleys with the main roof. There are several styles of dormers with rounded roofs, i.e., eyebrow dormers, segmental dormers, and barrel-roof dormers; in most cases, segmental and barrel-roof dormers include triangular vertical side walls (cheeks). In the eyebrow dormers (both steep and shallow) the dormer roof is moulded out of the main roof plane without interruption. The shallow eyebrow dormer tends to be much wider than it is high, whereas a semi-­ circular eyebrow dormer is relatively narrow and has a semi-circular roof.

Fig. 8: Gabled dormer

Gabled dormer

Eyebrow dormer (shallow)

Fig. 9: Barrel dormer

Shed dormer

Eyebrow dormer (semi-circular)

Fig. 10: Shed dormer (also monopitch ­dormer)

Dog-house dormer

Barrel dormer

Fig. 11: Dormer types

23

Dormer construction

Roof windows

The front of the dormer often consists of a prefabricated timber frame that is either placed on the rafters or directly on the floor beneath before the external cladding is fitted. In shed dormers, the shed rafters at the top end sit on the trimmed rafters. At the bottom end they are attached to the gable frame of the dormer. The triangular vertical walls of the dormer are called cheeks. In order to provide rigidity to the structure, these are usually lined with panels, which are lined on the outside with metal, clapboarding, slates, or tiles. However, it is also possible to insert glazing into the cheeks. The width and length of the dormer needs to be designed to suit the roof construction as well as the roofing material. Roof windows are almost always supplied and fitted as prefabricated elements. Typical products come in a range of versions with flashings to suit different roof coverings and constructions to ensure proper drainage; where the roofing material has back-ventilation, the roof window must not interrupt this. Common widths of roof windows are aimed at fitting the multiple widths of the space between rafters. Where several roof windows are fitted next to each other, they will have a main rafter between them and will be connected with special framing and flashing. Roof windows come with different opening options. In centre-pivot windows, the window sash is attached to the window frame midway along the side rails, which means that the upper half pivots into the room when the window is opened. A top-hung window is attached to the frame at the top edge and completely opens outwards. Sliding windows are rarer, but can also be fitted; the sliding sash can either be moved sideways beneath the roof or can overlap another part of the window that is fixed. For some years now, units are available on the market that combine a lower vertical glazing portion with an upper portion in the form of a top-hung window; the lower part reaches down to the floor and can be folded out to form a kind of balcony railing. > Figs. 12 and 13

Centre-pivot window

Schwingfenster

Fig. 12: Types of roof window

24

Top-hung window

Klappfenster

Combined roof window unit mehrteiliges

Dachfenster

Sliding window

Schiebefenster

Fig. 13: Fully fitted roof windows

25

Roof construction In sloping timber roof structures, a distinction is made between three basic systems: closed couple roof, collar roof, and purlin roof. In addition, there are roof structures that consist of solid materials such as concrete, aerated concrete or clay blocks, or steel; due to the high cost of steel construction, this is rarely used for domestic buildings. However, in buildings with large open spans, steel and concrete structures are regularly used due to their structural properties. All types of roof constructions can be designed with the structural members visible on the inside or lined with cladding. WOODWORKING JOINTS

Even today, most roof structures are built in timber. The individual elements of the structure are either joined by traditional woodworking

Fig. 14: Roof construction details

Fig. 15: Joint of rafter with the eaves purlin (also called wall plate) showing a bird’s mouth joint

26

Fig. 16: Mechanical connection of a two-part collar beam to the rafter and middle purlin using metal bolts

joints or using mechanical jointing devices, such as nail plates or bolts; in timber engineering, timber elements may also be joined using adhesives. Nowadays, traditional woodworking joints have made a comeback but are produced by way of digital machining. There are five different types of woodworking joint: > Figs. 15–17 —— End-to-end connections, like the bridle joint, are used to extend timber sections such as beams or purlins. —— Perpendicular joints are used, e.g., for inserting a trimmer. —— Rafter and tie-beam joints are used in roof construction, mostly for connecting rafters to timber tie beams. —— Corner joints are typically needed at the corners of wall plates. —— Notched joints are used to connect two timber sections that are offset and have a different orientation.

End-to-end joints

Half-lap joint (vertical also possible)

Bridle joint

Tabled joint

Bridle joint

Mortise and tenon joint

Haunched tenon joint

Half-lap joint

Bridle joint

Tabled half-lap joint

with front notch

with double notch

with rear notch

Dovetail notch joint

Cogged joint

Cross-notch joint

Perpendicular joints

Corner joints

Rafter and tie-beam joints

Notched joints

Fig. 17: Selection of carpentry joints for timber components

27

CLOSED COUPLE ROOF Construction

Dimensions

Closed couple roofs are the simplest form of timber roof construction. A triangular frame is formed of the two sloping timber members, the rafters, and the horizontal member at the bottom, the tie beam, or alternatively a ceiling slab. The two rafters leaning against each other are called a couple. At the point of contact, the rafters are fixed but not rigidly connected to each other. The term for this type of frame is hinged frame. Closed couple roofs consist of several pairs of rafters, the typical spacing of which is 40, 45, and 60 cm; where the rafters meet at the ridge, they are connected by a ridge board, which makes a longitudinal connection and facilitates fixing. The loads impacting on the rafters are made up of their own weight (dead weight) plus live loads (snow, etc.), which result in compressive force. They are also subject to bending as a result of loads impacting on the surface in perpendicular direction. The ridge beam is subject to tensile force. All connections must be detailed such that the relevant forces can be effectively transferred to the supporting structural elements, such as walls or pillars. Traditionally, the tie beams project out from the base of the rafters by about 20 cm. This creates an area that needs to be mastered with an additional timber member called a firring. Firrings are typically fixed to the side of the tie beam and have a shallower pitch than the main roof slope. > Fig. 21 Today it is more common to use a construction involving a concrete ring beam that absorbs the forces. To absorb longitudinal forces, it is necessary to brace the roof planes with additional members. These may take the form of wooden boards (wind braces), or flat steel straps that are attached diagonally across the rafters; alternatively, the entire roof plane can be covered with wooden boarding or large-format boards. > Fig. 22 Ideally, the slope of closed couple roofs should be between 25 and 50°; the clear span should not be more than 8 m as the cross-section of timbers for larger spans tends to be uneconomical. The advantage of this construction is that there are no upright members at all in the roof space. Where dormers or roof windows are to be fitted it is necessary to use trimmers and trimmer rafters. The cross-section of rafters varies significantly in different countries; in Anglo-Saxon countries the width is typically only 5 cm, with the height varying between 10 and 17.5 cm, depending on the span.

28

4

3 Isometric

4

Load scheme 3 1

pr nd

m

Be

Co k

ng

uc Dr

gu Bk i e un

g

uc Dr

eg

un g

Bi

eg

ck

Bi

Zug 3 6 3

7 4

2

6 7

7 1. Concrete slab 2. Ceiling joists

2 3. Ridge board 4. Rafter

2 plate 5. Wall 6. Ridge strap

7. Sprocket

Fig. 18: Isometric and load scheme of a closed couple roof

Bracing with wind braces on the inside of the rafters

GSPublisherVersion 70.85.88.100

GSPublisherVersion 70.85.88.100 GSPublisherVersion 70.85.88.100

Bracing with wooden boarding

Fig. 19: Bracing of a closed couple roof

29

on

k

gr u u nD Zug

si

uc

eg

6

4

Bracing with large-format panels

Bi

3

4

Tension

es

Dr

1

nd

1 5

Be

5

Closed couple roof on timber deck

pr

es

m

3

Co

4

on

5

si

Closed couple roof on concrete slab

COLLAR BEAM ROOF Construction

Like closed couple roofs, collar beam roofs form a triangular frame with the addition of a horizontal timber member, the collar beam. > Fig. 20 This collar beam absorbs compressive forces on the rafters, thereby reducing bending (deflection) of the rafters. In turn, this means that this type of roof can be used for larger spans of up to 15 m. For ease of repairs, collar beams may be fitted in pairs, with one member each on either side of the rafter. In order to be structurally effective, the collar beams should not be fitted at a point that is lower than 75% of the overall height from tie beam to ridge, measured from the bottom. Both the tops and bottoms of the rafters are fitted as in the closed couple roof.

Isometric

Load scheme

Collar beam roof 3

on si es pr

Tension

Queen post truss 3 2 5 6 1

Liegender Stuhl truss

3 2 5 7 1 8 1. Concrete slab 2. Ridge board

3. Rafter 4. Wall plate

5. Collar beam 6. Queen post

Fig. 20: Collar beam roof construction systems; isometric and load scheme

30

7. Principal rafter 8. Head plate

on

Compression

si

m

es

Co

pr

4 1

m

5

Co

2

PURLIN ROOF

In purlin roofs the rafters bear on horizontal structural members called purlins, which in turn are supported from walls or uprights called posts or stays. In order to be able to absorb horizontal wind loads, the posts must be braced with struts that are fitted parallel to the roof slope, a short distance from the rafters. The support member at the uppermost point of the roof is called a ridge purlin, that at the lowermost point is called an eaves purlin (or wall plate), and the intermediate one is called the middle purlin.

Isometric King post

Construction

Load scheme

5 5 4 4 6 6 2 2 1 1

Queen posts

5 5

3 3 2 2 1 1 6 6

King post and queen posts ­combined, with struts

5 5 4 4 3 3 2 2 7 7 6 6 1. Concrete slab 2. Wall plate (eaves purlin)

3. Middle purlin 4. Ridge purlin

5. Rafter 6. Post

7. Strut

Fig. 21: Purlin roof construction systems; isometric and load scheme

31

Types of purlin roof

Dimensions

The simplest form of purlin roof uses a vertical post, the so-called king post, to support the ridge purlin. > Fig. 21 In this case the rafters are supported by the ridge purlin and the eaves purlins. Vertical loads are mainly transferred from the ridge purlin downwards via the king post. In a more complex roof construction, the rafters are supported from the eaves purlin and a middle purlin. Here the middle purlins are supported on vertical posts called queen posts. In order to absorb horizontal forces across the roof, it is possible to fit an additional collar beam or straining beam. In that case, the top part of the roof is similar to a couple roof. In the case of larger spans and where rafters are longer than 7 m, both the two middle purlins and the ridge purlin are supported by vertical posts, a construction that combines the above-described systems. Where it is not possible to transfer the vertical forces from the ridge purlin via a vertical post owing to the plan layout beneath, the vertical post only goes down to the collar beam from where the loads are transferred via slanting bracing members, a construction known as king post truss. All the above design versions can be used for all the possible roof slopes. However, the spacing of purlins should not exceed 4.5 m.

Table 6: Overview of components in sloping roofs Component Sprocket

Drawing

Notes

Common sizes for average roofs

Pfosten for closed couple roofs Pfosten Pfosten Pfosten Pfosten Pfosten

8/12–10/22

Dachbalken Dachbalken Dachbalken

Richtholz Richtholz for closed couple roofs Richtholz Richtholz Richtholz Richtholz

12/12–14/14

Ridge purlin

Firstpfette Firstpfette Firstpfette Firstpfette Firstpfette Firstpfette

Sparren Sparren Sparren on walls or posts Sparren Sparren Sparren

14/16–16/22

Wall plate

Fußpfette Fußpfette Fußpfette Fußpfette Fußpfette Fußpfette

Strebe Strebe Strebe Strebe on the slab/external wall Strebe Strebe

10/10–14/16

Kehlbalken Kehlbalken Kehlbalken Kehlbalken Kehlbalken Kehlbalken

Vorholz Vorholz Vorholz Vorholz Vorholz may consist of two ­timber Vorholz

8/14–10/20

Kehlsparren Kehlsparren Kehlsparren Kehlsparren Kehlsparren Kehlsparren

Wechsel Wechsel Wechsel Wechsel Wechsel Wechsel with V-shaped bevel

8/14–8/22

Knagge Knagge Knagge Knagge Knagge Knagge

Windrispe Windrispe Windrispe Windrispe Windrispe Windrispe

Kopfband Kopfband Kopfband Kopfband 32 Kopfband Kopfband

Zange Zange Zange Zange Zange Zange

Aufschiebling Aufschiebling Aufschiebling Aufschiebling Aufschiebling Aufschiebling

Dachbalken Ceiling joists Dachbalken Dachbalken

Collar beam

Valley rafter

sections, one on each side of rafter

schiebling schiebling schiebling schiebling schiebling schiebling schiebling chbalken schiebling chbalken chbalken chbalken chbalken chbalken chbalken stpfette chbalken stpfette stpfette stpfette stpfette stpfette stpfette ßpfette stpfette ßpfette ßpfette ßpfette ßpfette ßpfette ßpfette hlbalken ßpfette hlbalken hlbalken hlbalken hlbalken hlbalken hlbalken hlsparren hlbalken hlsparren hlsparren hlsparren hlsparren hlsparren hlsparren agge hlsparren agge agge agge agge agge agge pfband agge pfband pfband pfband pfband pfband pfband elpfette pfband elpfette elpfette elpfette elpfette elpfette elpfette elpfette

Kehlbalken Kehlbalken

Vorholz Vorholz

Kehlsparren Kehlsparren Component Kehlsparren Drawing

Wechsel Wechsel Wechsel Notes

Cleat

Knagge Knagge Knagge

Windrispe for collar beams (pairs) Windrispe Windrispe

Kopfband Kopfband Kopfband

Zange with brace to post Zange Zange

Head plate

Mittelpfette Mittelpfette

Middle purlin Mittelpfette

Post

beneath the rafters

Texte sind nicht Bestandteil der Grafik, sondern dienen der Pfosten supports purlins Pfosten Texte sind nicht Bestandteil der Grafik, sondern dienen der einfacheren Zuordnung der Abbildungen innerhalb der Tabelle Pfosten Texte sind nicht Bestandteil der Grafik, sondern dienen der einfacheren Pfosten Zuordnung der Abbildungen innerhalb der Tabelle einfacheren Zuordnung der Abbildungen innerhalb der Tabelle Pfosten Pfosten GSPublisherVersion 73.78.81.100 Pfosten Richtholz GSPublisherVersion 73.78.81.100 Pfosten Richtholz Ridge board for easier fixing of GSPublisherVersion 73.78.81.100 Richtholz top of rafters Richtholz Richtholz Richtholz Richtholz Sparren Richtholz Sparren Sparren support the roofing Rafters Sparren material Sparren Sparren Sparren Strebe Sparren Strebe Strebe Strebe Strut for cross-bracing Strebe Strebe Strebe Vorholz Strebe Vorholz Vorholz Vorholz Tie-beam projection in closed couple roofs Vorholz Vorholz Vorholz Wechsel Vorholz Wechsel Wechsel Wechsel Wechsel Trimmer for openings Wechsel Wechsel Windrispe Wechsel Windrispe Windrispe Windrispe Windrispe Windrispe Windrispe Wind braces for wind bracing Zange Windrispe Zange Zange Zange Zange Zange Zange Zange Collar beam (paired) for horizontal bracing

Common sizes for average roofs

10/10–10/12

12/20–14/20

12/12–14/14

thickness from 22 mm

8/14–8/22

14/16

lengths 20 cm

8/14–8/22

flat steel straps

6/14–8/16

e sind nicht Bestandteil der Grafik, sondern dienen der echeren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle echeren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle echeren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle echeren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle encheren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle 73.78.81.100 encheren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle 73.78.81.100 encheren sind nicht Bestandteil der Grafik, sondern dienen der Zuordnung der Abbildungen innerhalb der Tabelle 73.78.81.100 cheren Zuordnung der Abbildungen innerhalb der Tabelle n 73.78.81.100

n 73.78.81.100

n 73.78.81.100

n 73.78.81.100

n 73.78.81.100

33

SOLID ROOF

Roofs made of prefabricated concrete components

Roofs using aerated concrete or clay blocks

The term solid roof refers to a roof constructed in concrete, porous concrete, or a combination of concrete and blocks. > Fig. 22 In contrast to the timber constructions described above, these roofs are usually built using prefabricated components that form a closed surface. It is also possible to use in-situ concrete when the objective is to create a roof with a free shape. Owing to the relatively heavy weight of the concrete, solid roofs perform well in terms of sound insulation. The construction is also beneficial in terms of low air permeability and, where it is possible to use the thermal storage capacity of concrete, it is also useful in terms of thermal performance. The prefabricated concrete components used in solid roofs are prefabricated in a factory where the other elements of the roof are also added, e.g., rafters, insulation, underlay membrane, and battens, which means that on the building site only the roof covering material has to be applied. Where the roof slabs consist of lightweight concrete, only the counter-battens are added in prefabrication; insulation and other roof components have to be fitted on site. > Chapter Roof battens The thickness of the slabs varies between approx. 5 cm for normal concrete with additional rafters and 16 cm in the case of lightweight concrete. In solid roofs using a block-and-beam construction, with blocks made of aerated concrete or clay, the direction of span and the spacing of beams are critical design parameters. The blocks are placed between the beams before in-situ concrete is applied on top. Like in the other construction methods, the additional roof construction consists of insulation, battens, underlay membrane, and the roof covering.

34

Solid roof based on normal concrete

Covering material Battens Counter-battens Underlay membrane Rafters/Air layer/Thermal insulation Concrete slab If needed: inside plaster/lining

Solid roof based on aerated concrete

Covering material Battens Counter-battens Underlay membrane Rafters/Air layer/Thermal insulation Aerated concrete planks If needed: inside plaster/lining

Roof with pot and beam construction

Covering material Battens Counter-battens Underlay membrane Rafters/Air layer/Thermal insulation Vapour barrier Pots between concrete beams If needed: inside plaster/lining

Fig. 22: Solid roof construction details

GSPublisherVersion 73.78.81.100 GSPublisherVersion 73.78.81.100

35

Roof construction layers TYPES OF ROOF COVERING

Thatched roofs

◯

Overlapping roofing materials

The main function of the roof covering is to reliably discharge precipitation water and to prevent the ingress of moisture not only from rain but also from drifting snow. Both materials and the fasteners should be weatherproof and ideally also fireproof. Depending on the detailing of the roof design, it may also be necessary to ensure that humidity can be discharged from the inside to the outside. > Chapter Building physics The choice of roof covering is not only governed by aesthetic aspects, but also by the slope of the roof, the shape of the roof, and the roof construction. A number of different materials are available, which result in different detailing and even roof shapes. Thatching is a traditional form of roof covering, which is still used in certain regions. Roofs covered in thatch tend to have a slope of between 40° and 50° because the lift-off forces generated by wind tend to be small. The roofing material consists of overlapping thatch bundles that are attached to battens. The material covering the ridge tends to be different to the main thatch coatwork; straw, heather, and sedge can be found, as well as plastic straw, or roof tiles. Overlapping roofing units are available in flat and curved styles; ­typical flat units are slates, wood shingles, stone slabs, and plain tiles made of concrete, fibre cement, or clay. They are available in different shapes, i.e., rectangular, rhombic, square with a rounded corner, or square at the top and rounded at the bottom (known as beaver-tail tiles). The units used in valleys, at the eaves or ridge, and at other intersection points are usually industrially prefabricated form pieces. The lowest standard roof pitch varies for different roofing materials and laying methods. The slope of roofs covered in fiber cement roof slates can be as shallow as ­approx. 20° without additional measures. There is an

Fig. 23: Roof construction in progress: underlay membrane, counter-battens, battens, and roof covering

36

a­ dditional ­advantage to using this material because the same units can often also be used for cladding the walls. The lowest standard roof pitch for roofs covered with slates is between 22° and 30°, depending on the laying method. Wood shingles can be used on roofs with a pitch of 71° or more if laid in two layers; however, it is more common to lay three layers, which means that roof pitches of between 22° and 90° are permissible. Flat overlapping roofing units are normally fastened by nailing them to battens. The advantage of formed or profiled roofing units (pantiles, monkand-nun tiles) over flat ones is that the roof pitch can be shallower, and a single layer is sufficient; materials may be concrete or clay. In contrast to flat units, these units are profiled such that they overlap on three sides. The oldest form of roof covering with profiled roof tiles is called monk-and-nun tiles. In this system, conically shaped tiles are laid one row face-up covered with another row face-down. This means that the tile on top is concave and allows the water to run into the convex tile below, from where the water drains into the gutter. Modern roof tiles are shaped in such a way at the edges that they engage with the adjacent tiles at the top and sides in order to prevent the ingress of water. The lowest standard roof pitch for profiled tiles starts from between 22° and 25°. In addition to the small roofing units described above, it is also possible to use large-format sheets in combination with specially formed units. Corrugated fibre cement sheets are large-format units attached to a subframe with overlapping edges. For roofs with a pitch of less than 12°, it is necessary to resort to bitumen or tar-based roofing felt. The detailing on the lateral edges usually consists of metal flashing. It is also possible to cover very shallow roofs with a pitch of down to 5° using very large-format materials. They usually consist of metal sheeting, such as aluminum, zinc, galvanized steel, or copper and are fitted in the form of shaped units, e.g., trapezoidal or corrugated sheeting, or in the form of plain metal sheeting that is shaped at the overlaying edges with seams in different configurations.

◯ Note: The lowest standard roof pitch refers to

the lower limit of roof pitch at which a certain roofing ­ aterial has been proven to be rainproof. In certain m ­situations it is possible to adopt a lower roof pitch for that material provided additional measures are carried out. The minimum roof pitch is the lowest possible roof pitch for the given roofing material.

37

Pantiles/monk-­ and-nun tiles

Large-format roofing materials

Fig. 24: Roof covered with flat units

Fig. 25: Roof covered with profiled pantiles

Fig. 26: Roof covered in metal sheeting

Flat roofing units

German slating system

Overlapping rectangular units

Rhombic units

Beaver-tail tiles

Profiled roofing units

ca. 40-60cm

Monk-and-nun tiles Profiled roof panels and metal roofing

Corrugated panels Fig. 27: Selection of roofing materials GSPublisherVersion 73.78.81.100

38

GSPublisherVersion 73.78.81.100

GSPublisherVersion 73.78.81.100

GSPublisherVersion 73.78.81.100

ca. 40-60cm

Interlocking pan tiles ca. 40-60cm

ca. 40-60cm

ca. 40-60cm

ca. 40-60cm

ca. 40-60cm

ca. 40-60cm

Metal sheet with standing seam

ROOF BATTENS

Whereas large-format roofing materials are attached to the substructure with screws, nails, bolts, or clips, roof tiles have a nib, which means that they are often simply laid on horizontal battens. Where an underlay membrane is used on top of the rafters and the roof pitch is relatively shallow, and flat roofing units are used, it is usual to also use counter-­ battens parallel to the rafters. > Fig. 29 The size of the roof battens depends on the weight of the covering material and the spacing of the rafters, as well as the quality of the timber. Where smaller roofing units are used, such as plain tiles, the ­battens are spaced much closer together than those for pantiles, for example, and are therefore also smaller; some common sizes are: —— Up to 75 cm rafter spacing: 30/50 mm —— Up to 90 cm rafter spacing: 40/60 mm However, smaller-sized battens can be used for smaller roofing units and when the rafters are closer together. The spacing of battens depends on the roof slope, as well as on the type of roofing units and laying method. In order to determine the batten spacing it is necessary to first of all determine the overall length of the roof slope. This is approximately the same as the length of the rafter. Next, the detailing of the eaves has to be decided. If the roof covering is to project beyond the end of the rafters, the total length is different from what it would be if it were to finish flush with the rafters. It is usual to opt for a projection that is equivalent to the overlap of the roofing units. The design of the eaves detail determines the spacing of the bottom two battens. Next, the distance between the top batten and the ridge point has to be established. This is determined by the design of the ridge detail. Now the spacing of the intermediate battens can be calculated by dividing the clear space between the top and bottom battens into equal parts. > Fig. 28 3

2

1

4

5

cing n spa batte idge r t a g spacin

cing n spa batte eaves t a

n batte cing n spa pe lo s f batte of roo length total

1. Counter-battens 2. Main battens 3. Roof tiles 4. Uppermost roof tile 5. Ridge tile

Fig. 28: Detail of roof covering and battens

39

Dimensions

ROOFING MEMBRANES

Underslating

Breather membrane

Waterproof underlay membrane

Normally, the roofing material will be sufficient to keep out precipitation water. However, in certain situations, additional measures are required in order to prevent the ingress of water when there are strong winds or drifting snow, or when the roof has a shallower pitch, the attic space needs to be fully protected, or a lot of snow and rain is expected due to the building being in an exposed position. The simplest form of additional protection is the underslating. This is a type of roofing membrane that allows the construction to be back-­ ventilated. It means that the membrane does not lie flat on a surface but rather dips between the supporting rafters. When additional ventilation is required, it is possible to fit counter-battens on top of the rafters and the underslating. This is necessary where the membrane does not dip between the rafters. Underslating usually consists of fabric-­reinforced plastic membranes. When the additional protection membrane is fitted flat on a continuous surface, such as closeboarding, a breather membrane is used. Breather membranes are considered to be rainproof. They are fitted below the battens and counter-battens. In certain situations, usually when the attic space is used for habitation, an additional protection layer is fitted beneath the roofing material. This consists of membranes that are joined together by welding or with adhesive. A distinction is made between a rainproof and a waterproof system. In a rainproof system, it is permitted to have openings that are needed for the construction. The membranes are placed underneath the battens and counter-battens. In a waterproof system, no openings are permitted. In this case the counter-battens are underneath the membrane, i.e., the membrane is fitted between the battens and counter-­ battens. In all systems it is important to ensure that any water collecting on the membrane can discharge at the eaves and be drained away via the gutter. In addition, it is important to ensure that the space beneath the membrane is adequately ventilated.

Without counter-battens

Fig. 29: Underlay membranes with and without counter-battens

40

With counter-battens

INSULATION

Where the attic spaces are well-ventilated and not used for habitation, the insulation is usually not fitted in the roof plane but rather to the horizontal slab forming the ceiling of the top floor as this is cheaper and easier. However, when the attic space is to be used for habitation and therefore is to be heated, the entire space must be insulated on all sides like the rest of the house in order to meet thermal insulation standards. In this case it is important to ensure that the insulation of the external walls continues without interruption and that thermal bridging is avoided. The thermal insulation material can be fitted between the rafters or on the inside of the roof slope, with the former obviously saving some space. The thickness of the insulation depends on the thermal insulation requirements and may not be the same as the depth of the rafters. Where this is the case, it is possible either to choose an insulation material with better insulation properties that will fit into the space between the rafters, or to apply two separate layers of insulation, one between the rafters and another thinner layer fitted either on top of them or on the inside roof slope. Where the insulation is fitted between the rafters, the insulation is interrupted by these but, in the case of a timber construction, this is not considered a thermal bridge. > Fig. 30 and Chapter Building physics When the insulation fitted between the rafters does not take up the entire available space, there will be a gap between the insulation and the underlay membrane, which is useful for the purpose of back-­ventilation. Where the space between the rafters is completely filled with insulation, additional measures may be necessary to ensure ventilation of the roof construction. Where it is intended to keep the structural roof members open to view, it is possible to apply the insulation on the outside of the roof slope, in which case closeboarding on top of the rafters is needed.

Insulation between the rafters

> Fig. 31

On the inside of the insulation, it is mandatory to fit a vapour barrier, which must be sealed airtight and bonded at all seams, edges, and any penetrations. The vapor barrier ensures that the humidity from the inside air cannot penetrate the thermal insulation material or the roof construction through diffusion. This means that the insulation layer is protected against the ingress of water on the inside by the vapour barrier and on the outside by the underlay membrane. Where the attic space is not ventilated and the space between the rafters is entirely filled with insulation, counter-battens must be fitted on top of the underlay membrane to ensure that any water – either as a result of condensation or as water ingress – can be discharged via the air gap. Ventilated roof constructions have this air layer directly above the insulation, which means that it is easier to discharge any penetrating humidity.

41

Vapour barriers

Attic with insulation on the top floor slab only

Fully insulated attic

Attic insulated up to the collar beam and dwarf walls

Attic insulated up to the collar beam

Fig. 30: Insulation in attics

42 GSPublisherVersion 70.85.88.100

Section

Layers

Insulation on ­rafters, with metal covering

Metal sheet roofing Separating layer Closeboarding Thermal insulation Vapour barrier Closeboarding Rafters If required: inside lining

Insulation between rafters with air gap

Roof covering Battens Counter-battens Underlay membrane Air gap Thermal insulation Vapour barrier Inside lining

Insulation between rafters without air gap

Roof covering Battens Counter-battens Underlay membrane Thermal insulation Vapour barrier Inside lining

Insulation between rafters with additional insulation beneath rafters

Roof covering Battens Counter-battens Underlay membrane Air gap Thermal insulation between rafters Thermal insulation beneath rafters Vapour barrier Inside lining

Insulation between rafters with additional insulation on top of rafters (e.g., in refurbishments)

Roof covering Battens Counter-battens Underlay membrane Insulation on top of rafters Insulation between rafters Vapour barrier Inside lining

Fig. 31: Roof construction details with different positions of thermal insulation

43

DRAINAGE DETAILS

Sizing

Gutters

Contact corrosion

Internal gutters

Any water falling on sloping roofs is discharged along the plane of the roof and via valleys and eaves. Here, precipitation water and condensate is collected in gutters, from where it is discharged via downpipes. To determine the size of the system components, it is necessary to establish the expected amount of rainwater; this can be calculated from the rain yield factor > Tab. 6, the effective roof plane, and a discharge coefficient. In this context it is important to remember that beyond the normal rainwater yield, there may be heavy rain events and, in areas where snowfall is to be expected, meltwater must be discharged in addition to precipitation water. Where rain gutters are fitted on the outside, it is not a great problem if these occasionally overflow; however, where gutters are fitted internally, it is vital to ensure that any emergency overflow does not cause damage to the building fabric. Gutters can be fitted at the eaves level with a shallow fall or without any fall using height-adjustable brackets. The spacing of brackets depends on the respective system, but as a general rule should not exceed 90 cm. The gutters should be slightly tilted towards the outside so that any overflowing water is discharged away from the building. The individual gutter lengths are joined with joining pieces and closed at the ends with end pieces. The water is discharged from the gutters to downpipes via so-called swan-neck pipe sections or via hoppers. The downpipes are fitted to the external wall using pipe clips. The bottom part of the downpipes is sometimes subject to mechanical impact and may therefore consist of a different type of material. This material is typically stronger, and this section of the pipe often has an inspection opening for checking and cleaning. Gutters and downpipes are available in angular or round cross-sections and in different materials. Where different metals are in contact with each other, it is important to ensure that there is no chemical reaction between them, such as contact corrosion, and that no stresses are generated due to differential expansion of the materials. For example, copper gutters and downpipes may only be fitted with steel brackets and clips that are coated with copper. On the other hand, aluminum gutters can be fitted with galvanized steel brackets or aluminum brackets. For gutters consisting of zinc or galvanized steel, galvanized steel brackets and clips are available. Internal gutters are those that are not installed on the outside of the gutter board along the eaves. They are used when the gutter is not supposed to be visible and the roof does not have an overhang. With this type of gutter, more stringent requirements apply because any overflowing water due to damage, blockages, or similar issues cannot discharge outside the facade but will collect inside the construction. In this case an additional drainage layer has to be formed beneath the gutter using ­waterproof membranes. In addition, emergency overflow outlets and larger pipe diameters are needed.

44

Table 7: Average design rain yield in litres per second, per hectare for different countries as per DIN EN 12056 Country

Average design rain yield

Germany

300 l/(sxha)

France

500 l/(sxha)

Netherlands

300 l/(sxha)

Switzerland

300 l/(sxha)

Table 8: Safety coefficients as per DIN EN 1056-3 Situation

Safety factor

Gutters fitted outside the gutter board

1.0

Gutters fitted outside the gutter board where any ­overflowing water is unwanted, e.g., above entrances to public buildings

1.5

Internal gutters and, in all situations, where it is possible that heavy rainfall can occur or where it is possible that blockages cause the water to drain into the building ­fabric

2.0

Internal gutters in buildings where special protection is required, e.g.: – Hospitals, theatres – Sensitive communication facilities – Warehouses for substances that will emit toxic or flammable gases when exposed to moisture – Buildings where special works of art are stored

3.0

45

Flat roofs A flat roof is a roof with a pitch of up to 5°. Owing to the shallow pitch, flat roofs are suitable for roof greening, roof gardens, terraces, drive-on surfaces, or for placing technical equipment such as solar collectors or ventilation equipment. Flat roofs are not finished with the roofing materials used for sloping roofs, but rather are finished with waterproof membranes that fulfill stringent requirements regarding waterproofing and the discharge of water. Compared to sloping roofs, flat roofs are more ­exposed to the suction effect of wind. It is therefore necessary to mechanically secure the covering materials, which tend to be lightweight. However, mechanical fixing devices penetrate the membrane. CONSTRUCTION

Like in sloping roofs, the construction of flat roofs can involve reinforced concrete, steel, and timber structures. Flat concrete roofs are most common in apartment and commercial buildings; steel structures are usually used for large industrial buildings. Where timber or steel framing is used for the roof construction, it is necessary to form a continuous surface that supports the additional roof construction layers; these surfaces may consist of various types of sheeting such as trapezoidal sheeting.

Fig. 32: Steel structure

Fig. 33: Reinforced concrete flat roof

46

TYPES OF ROOF CONSTRUCTION

There are three different types of roof construction that differ in the way the layers are fitted in the roof structure > Fig. 34 as described below. A warm roof is a roof without back-ventilation in which the waterproofing layer is placed above the thermal insulation; the insulation is also used to create the fall for the water drainage towards the roof gullies. A priming coat and the vapour barrier are applied beneath the insulation. In order to provide better protection to the waterproofing layer, it is also possible to invert the construction. In this case the insulation layer is placed above the waterproofing layer, which must consist of hydrophobic material. In this situation it is not possible to create the fall towards the gullies within the insulation layer, which means that a screed with a fall has to be applied beneath the waterproofing layer. The third type of construction is called a cold roof, which means the roof is ventilated. This type of roof is similar to a rafter roof, with insu­ lation between the rafters, and is usually used in the context of timber constructions. On the inside this roof needs a vapour barrier, which is covered by the cladding. The insulation is placed between the timber joists; it is important here that the insulation does not fill the entire space between the joists in order to allow sufficient ventilation. The joists support closeboarding, which in turn supports the waterproofing layer and the layer selected for protecting the surface.

Section Unventilated roof – warm roof (concrete slab)

2% fall 2% fall

Unventilated roof – warm roof (steel girder ­construction)

Warm roof

Inverted roof

Cold roof

Layers Waterproofing layer Vapour pressure equalizing layer Insulation with fall, min. 2% Vapour barrier Priming coat Reinforced concrete slab

Waterproofing layer Vapour pressure equalizing layer Insulation Vapour barrier Trapezoidal sheet Steel girder with fall 2% fall 2% fall

Fig. 34: Flat roof construction details (Continued on page 48)

2% fall 2% fall

47

Section

Layers

Inverted roof

fall 2% 2% fall

Ventilated roof – cold roof

Surface protection e.g., gravel, min. 5 cm Filter layer Thermal insulation, rigid Waterproofing layer Screed laid to fall Reinforced concrete slab Modification of warm roof Insulation on the wet side above the waterproofing layer  Not all insulation materials are suitable  The waterproofing layer must be protected against damage Roofing material Underlay membrane Closeboarding Air gap, min. 15 cm Thermal insulation between the rafters Vapour barrier If needed: inside lining

Fig. 34: Flat roof construction details (Continued from page 47)

CONNECTION DETAILS

Where a vertical building component meets the horizontal roof surface, waterproof connection details must be provided; examples include the walls of the top part of an elevator shaft, stairwells leading onto the roof, and the joints between rooflights and the roof. The basic rule is that, in roofs with a slope of 5° or less, the waterproofing has to be carried up on the vertical surface by 15 cm and, in roofs with a slope of over 5°, it has to be carried up by at least 10 cm above the roof surface in order to prevent the ingress of splash-back water or any water that may have formed through pooling. Depending on the type of sealing material used, it may be necessary to opt for mechanical means of fixing, such as clips or clamping rails. Where the waterproofing layer consists of liquid plastic, it may be possible to omit any additional fixing devices. In addiGSPublisherVersion 70.85.88.100 GSPublisherVersion 70.85.88.100 tion, the top edge of the upstand must be secured against rain by overlapping it with the cladding used on the vertical surface. In the case of penetrations of the flat roof, it is important to consider whether the sealing detail needs to be flexible or can be rigid. The manufacturers of waterproofing foil membranes often provide special form parts to master the internal and external corner details or the rounded surfaces of pipes (pipe sleeves). The sealing detail at openings, such as patio doors, needs to be given special consideration. The reason is that, if the upstand is carried up by 15 cm above the roof covering, the threshold of the door will be that much higher than the internal floor surface and the external roof surface unless special measures are taken to compensate for the height

48

Fig. 35: Liquid plastic used as a sealing detail between the roof surface and a steel construction member

Fig. 36: Sealing detail, with upstand fixed mechanically with a clamping rail

difference. For example, it is possible to raise the floor inside of the door, which means that there would only be a step down from the door onto the roof surface. It is, however, also possible to reduce the height of the upstand to a minimum of 5 cm if a drainage channel with connection to the roof drainage is provided in front of the door.

EDGE DETAILS

The design of the edge details of flat roofs requires careful consideration. An upstand needs to be formed at the edge of the roof to allow for the build-up of layers and to contain any surface water; this may be located in line with the external wall or out of line, either projecting or recessed. This upstand can take the form of a parapet or an edge profile. A parapet is the continuation of the wall above the level of the roof and usually consists of brickwork or concrete on the vertical surface of which the waterproofing layer can be applied. > Chapter Roof connections The parapet height can vary, and it can also be used as a fall-prevention device if the height complies with the minimum requirement. The top of the parapet needs to be protected from the weather; a common option is metal flashing that needs to be applied so that it forms a drip edge on both sides, with a minimum projection of 2 cm from the facade. This flashing covers the entire width of the parapet and should have a slight slope towards the roof surface. Edge details using special profiles usually involve a timber member in the plane of the insulation to which such profiles are fixed. The shape is such that the waterproofing layer on the inside can be pressed into the profile and the profile wraps around the edge of the roof on the outside, overlapping the facade. The outer edge of the parapet flashing or an edge profile needs to include a drip edge to ensure that any rainwater does not run behind the facade or the flashing.

49

Avoiding thermal bridges

To avoid thermal bridges, edge details must be appropriately insulated. > Figs. 37 and 38, Chapter Building physics In the case of roof projections and parapets, it is also possible to insert thermal separation to ensure that these parts are not connected to the insulated building; in this case, these parts remain without insulation. To do this, a loadbearing insulation element (e.g., Isokorb®) is inserted in the loadbearing layer, which can ­absorb the loads but, in contrast to a continuous concrete slab, largely consists of materials with low thermal conductivity and thereby reduces any heat loss. The advantage of thermally separating these building components is primarily that no insulation needs to be applied and hence they appear less bulky.

Fig. 37: Detailing of insulated parapet

50

Projecting roof slab, thermally separated

Projecting roof slab, insulation all around

Edge of roof with concrete parapet, thermally separated

Edge of roof with concrete parapet, insulated all around

Edge of roof with brick parapet

Edge of roof with proprietary profile

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Fig. 38: Edge of roof details GSPublisherVersion 73.78.81.100

51 GSPublisherVersion 73.78.81.100

ROOF LAYERS

Supporting surface of a flat roof

Separating layers and bonding courses

Vapour barrier

As in a sloping roof, the overall roof construction has to fulfill the requirements of building physics, must discharge water from the outside and within the system, and must be windtight. To this end, different layers and materials are used, which have to be designed such that the whole construction and the materials work well together. The design of roofs with a pitch of 25° or less can follow the rules of flat roof design, as well as those for sloping roofs. However, when such a roof with a shallow pitch is constructed like a flat roof, it is important to ensure that the different layers cannot slide down and, in particular, that they cannot be dislodged through wind suction. The surface that supports the weatherproof layer of the flat roof can be the structural deck (e.g., a reinforced concrete slab) or a continuous surface attached to the structure, such as closeboarding, trapezoidal sheeting, or the thermal insulation. > Fig. 40 On top of a closeboarding layer, it is usually necessary to place a separating membrane. Where it is intended to improve the adhesion of the top layer to the structural base, it is possible to use bonding courses in the form of primers, usually on the basis of bitumen. Where the substrate is uneven, it may be necessary to apply a levelling layer. Separating membranes can consist of bitumen membranes, fleeces, or foam matting. > Fig. 39 Vapour barriers usually consist of loosely laid, or partially or fully bonded bitumen or plastic membranes and are particularly resistant to vapour diffusion. At the edges of vertical building components or penetrations, the vapour barrier must be continued to the top of the ­insulation layer, where it has to be attached. A vapour barrier can also contribute to the airtightness of the roof. In addition, a bonded vapour barrier can be useful as a temporary waterproofing layer during the construction phase. > Fig. 40

Fig. 39: Separating layer applied to trapezoidal sheeting

52

Fig. 40: Vapour barrier and temporary waterproofing layer consisting of a liquid bitumen coating and bitumen membrane

For the thermal insulation beneath the waterproofing layer, a range of insulation materials is available on the market. Depending on the use of the roof, the selected material has to have adequate compressive strength. However, in the case of inverted roofs, it is essential to use only waterproof insulation materials that do not lose their insulation properties when exposed to moisture, such as EPS, XPS, or glass foam. Insulation materials fitted in areas close to openable components covered by fire safety regulations or above fire walls have to be selected in compliance with the particular requirements, such as mineral wool. Where roofs are covered with trapezoidal sheeting, these sheets may have to rest on insulation strips with a matching shape in order to create a flush bearing surface without gaps. > Chapter Materials used In order to equalize the vapour pressure beneath the waterproofing membrane, it may be necessary to install an equalization layer. Bitumen or plastic sheeting is loosely laid or bonded intermittently. The waterproofing layer of the flat roof is its most important part as it serves to discharge water that falls on the roof. Possible membranes include bitumen sheeting, plastic sheeting, and liquid waterproofing materials. As a rule, bitumen membranes used as the waterproofing layer on flat roofs are applied in several layers. These layers are installed with overlaps, working in longitudinal and crosswise directions. The minimum overlap in multilayer systems is 8 cm; in single-layer systems it is 10 cm. The overlapping areas must be fully bonded. > Fig. 41 As a rule, plastic waterproofing membranes are applied in single layers only; like bitumen membranes, they can be used for unused and walk-on roofs, as well as for green roofs covered with a layer of earth. Depending on the intended function, membranes may be based on PVC, PIB, or flexible polyolefins, with or without additional reinforcement. In order to prevent excessive thermal expansion of the membrane due to solar radiation, it is usual to opt for light colors. > Fig. 42

Fig. 41: Roof with bitumen waterproofing layer

53

Thermal insulation

Vapour pressure equalization layer

Waterproofing

Bitumen membranes

Plastic waterproofing membranes

Imposed loads/ gravel layer

Here too, depending on the material and installation method, the overlapping edges must be firmly bonded to each other. However, the membranes themselves do not have to be bonded to the roof in their entirety; intermittent bonding or loose laying with additional fastening with battens at the edges is sufficient. As an alternative to plastic membranes, it is also possible to use liquid waterproofing materials for the entire roof surface. Depending on the substrate, it may be necessary to carry out some preparatory work, for example, removing any dirt and/or creating a better bonding key by roughening the surface. Liquid plastics come as single- or multi-­ component materials and may be further reinforced during application by laying reinforcement fleece. In contrast to the membrane systems, these systems do not require mechanical fastening at the edges. It is important, though, that the reinforcement fleece mats overlap. Where such roofs are intended to be walked on, it may be necessary to apply an additional protection layer. It is also possible, depending on compatibility, to use liquid waterproofing materials in combination with bitumen or plastic membranes, for example, in the area of penetrations or connections. In certain situations, e.g., when the top waterproofing layer is not fit to support loads, it is possible to install additional protection layers on top of bitumen or plastic membranes. These can be installed on the entire area in the form of a gravel layer, or as additional hardwearing membranes; where additional protection is only required in certain areas, such as walkways, a range of different materials may also be applied. Where the layer of gravel is intended to prevent loose-laid membranes from lifting off, the minimum required thickness is 5 cm or more, depending on the height of the building. Where the waterproofing layer permits, it is also possible to lay solid slabs as a walk-on base. > Fig. 43

Fig. 42: Roof with plastic waterproofing membrane

54

Fig. 43: Flat roof with layer of gravel

GREEN ROOFS

On flat roofs it is very common to install so-called “green roofs”; this may even be a requirement of the building permit, as the planting on the roof compensates for the vegetation lost beneath the building. Green roofs are not only beneficial to the microclimate, but also delay the drainage of water by storing such water in the substrate and drainage layers. In the design of green roofs, it is important to ensure that the roots of the plants cannot damage the waterproofing layer (e.g., by installing root-­protection membranes) and to take into account the additional load of approx. 70 to several hundred kg/m² in the structural calculations. In addition, it may be necessary to provide narrow areas of gravel along the edges, around penetrations, and above fire compartment walls (usually spaced 40 m apart). Green roofs are also possible on sloping roofs, provided certain additional measures are taken. From a roof pitch of approx. 15°, additional horizontal members are installed on the roof that prevent the substrate from sliding down the roof surface. A distinction is made in green roofs between extensive and intensive planting, with the extensive system being shallower. Extensive green roofs > Fig. 45 require less maintenance and typically support plants such as mosses or succulents. Intensive green roofs > Fig. 44 require a much thicker layer of soil and therefore impose greater weight on the roof; these roofs can support trees, grasses, and herbaceous perennials.

Fig. 44: Roof with gravel layer and intensive greening approx. 1 month after planting

Extensive and intensive green roofs

Fig. 45: Extensive green roof approx. 5 years after ­completion

55

Section

Layers

Extensive green roof construction on steel girders

Plants/vegetation mat Sedum (min. 8 cm), thinner layers possible if needed Drainage element Protection fleece Waterproofing layer Vapour pressure equalizing layer Insulation Vapour barrier Trapezoidal sheeting Steel girder

Intensive green roof construction on reinforced concrete slab

Plants Substrate (approx. 20–40 cm) Filter fleece Drainage/water storage element Protection fleece/root protection Waterproofing layer Vapour pressure equalizing layer Insulation Vapour barrier Reinforced concrete slab

Fig. 46: Details of extensive and intensive green roof construction

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DRAINAGE DETAILS

In order to prevent the formation of puddles on the roof, the waterproofing layer, which is used to discharge the water, must have a minimum fall of 2% towards the points of discharge. A common solution is the installation of insulation with a fall, because the loadbearing structure of a flat roof does not usually have a fall. In the case of large industrial buildings, the beams supporting the roof can be installed at an angle to create the required fall. Where the fall is created with the sloping insulation, it is important to ensure that the minimum insulation thickness is still maintained at the thinner end. This can be achieved by installing an even layer of insulation of the minimum thickness and adding ­prefabricated sloping

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56

boards to create the fall. Alternatively, it is possible to lay a sloping screed beneath the insulation layer to create the necessary fall. The water is discharged towards the lowest points in the roof; these can be either external or internal, with discharge pipes running through the building to the drainage pipes in the ground. Internal drainage systems must have appropriate thermal insulation and present a leakage risk. Where the drainage is to take place outside the building, it is possible to create a drainage channel along the edges of the roof using the membrane; from there, the rainwater is discharged to the ground drainage pipes via downpipes that are either within the layer of the facade or surface-mounted. For both types of drainage, it is possible to use a gravity or a siphonic drainage system. > Fig. 47 In gravity drainage systems, the water from each discharge point is conducted via a downpipe to the ground drainage pipe, which is laid with a fall. In the siphonic drainage system the number of downpipes is significantly reduced because the water from the discharge points is collected in a pipe from where it runs to a downpipe; the discharge down the downpipe creates negative pressure in the pipe, which increases the speed of drainage. All roof drainage outlets must be fitted with a device to prevent leaves and gravel entering and blocking the system. The number and size of roof drainage outlets has to be calculated using specific rules and depends on a number of factors, such as the size of the roof area, the roof construction and drainage system, and ­figures for the expected rainfall – the normal rain yield factor and the 100-year rain yield factor. Layers of gravel and roof greening systems have a positive effect on drainage, because the overall amount of rainwater to be drained is significantly reduced as it is stored in these layers and discharged over longer periods of time. All regular rainwater discharge outlets need to be fitted with an additional emergency outlet that ensures that any water from exceptional heavy rain events can still be discharged. This outlet needs to be placed above the lowest point. This ensures that water cannot pool on the roof and cause damage. However, the water from these emergency outlets must not be conducted to the normal drainage pipes; this is to ensure that drainage can still take place in such an emergency when there is a blockage in the regular pipe system. This means that the water conducted via the emergency drainage pipes is discharged via spouts inserted in the parapet or facade, or via a surface-mounted downpipe discharging openly to the ground, from where it can run off. > Figs. 49 and 50 To mark the layout of the drainage system, a drainage plan is produced that provides all the information, including falls, discharge points, valleys, and ridges. > Fig. 48

57

Gravity/ siphonic drainage

fall Gravity drainage

Siphonic drainage

with

out

fall

fall

Fig. 47: Schematic illustration of gravity and siphonic drainage systems

with

out

fall

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Fig. 48: Drainage plan

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Fig. 49: Installation of a roof outlet in the waterproofing layer

58

Fig. 50: Emergency drainage with external downpipe, ­hopper, and freely discharging spout

Additional components FALL PREVENTION ON ROOFS

There are a number of reasons why safety devices must be provided on roofs; these include the installation and repair of roofing materials and waterproofing membranes, maintenance work, access to technical equipment, and the care of plants that are part of a green roof. Such safety devices, including fall-prevention systems, must be taken into account in the design. The choice of safety system depends on the roof pitch, the distance of any pathways or work areas to possible fall edges > Fig. 51, the use of the roof in terms of how often people walk on it, and the visibility of the roof surfaces. All systems must fulfill the requirements of Health & Safety at Work regulations; this may involve permanent safety devices (collective protection) or the use of personal protection equipment, both of which need to be taken into account in the design. For roof slopes exceeding 20° with an eaves height of > 3 m, it is a mandatory requirement to provide safety devices. As a rule, roof safety hooks are fitted in accordance with EN 517. > Fig. 52 The hooks are fastened to the structural roof members with nails and can be used for hanging roof ladders or for attaching roofing platforms; they may also feature integrated eyelets for attaching safety harnesses. There is a distinction between type A hooks, which are used to secure against falling in the direction of the pitch of the roof, and type B hooks, which can withstand tensile forces both in the direction of, and perpendicular to, the pitch of the roof. Occasionally, individual fastening devices or rope-securing systems are ­fitted to sloping roofs (see description below).

1. Fall edge 2. Risk of fall area 3. Fall height

>60°

Fig. 53. Railing systems that are self-supporting or held in place by an imposed load are easy to install subsequently and have the advantage that the rainproof skin of the roof does not have to be pierced. Furthermore, such railings are not limited to the edge areas, and it is possible, for example, to install them on either side of a pathway across a roof. Where railings are installed at the parapet or on the roof surface, it is critical to ensure

Fig. 53: Railing fastened with Z-angles beneath the parapet coping during and after installation

60

that the fixings do not damage the roof skin or that no thermal bridges are created (e.g., when attaching a railing to the side of a thermally insulated parapet). Various systems are available, such as railings attached to the vertical face of the facade or on the inside of the parapet, on top of the parapet, attached beneath the parapet coping, and directly to the roof surface. > Fig. 54.

Railing fastened to the inside of the parapet

Railing fastened to the top of the parapet

Railing fastened to the roof surface

Freestanding self-supporting railing

Fig. 54: Railing fastening methods

61

Anchorage systems

◯

Anchorage systems are available in the form of linear systems and as anchorage point systems > Fig. 55. All systems can be installed within the roof surface or close to openable components. The linear rail or cable safety systems > Fig. 56 can also be used for attaching safety ropes at high level, e.g., where there are building recesses. Individual anchorage points may be chosen because they are not very conspicuous; however, they should only be used when the roof is infrequently accessed because the additional individual safeguarding process is relatively involved. Only one person can use an anchorage point to attach a safety harness, and because the distance of the work to the fall edges may be continually changing, the safety rope may have to be adjusted regularly; in addition, it may be necessary to disconnect the rope and reconnect it to other anchorage points. Another point of concern is the fact that, similar to linear systems, the roofing membrane is pierced in many places. By contrast, rail- and cable-based safety systems can be used by several people at the same time. Where this is possible with the system used, it may only be necessary to attach the safety device once at the entrance. Compared to rail systems, cable safety systems have the disadvantage that they have to be re-tensioned regularly because slack cables could damage the roof skin or, in the case of roofs with a gravel layer, could sustain damage themselves.

Fig. 55: Individual anchorage point in a roof with a waterproofing membrane during and after installation

Fig. 56: Cable safety system

◯ Note: At rooflights/fenestration bands, it is not always necessary to provide fall-prevention devices, provided the component has its own safety device, e.g., in the form of a grid.

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PHOTOVOLTAICS AND SOLAR COLLECTOR SYSTEMS

Even though questions have been raised regarding the environmental benefit of the production of photovoltaic systems, they are nevertheless widely used for the production of electricity from solar radiation, ­either to feed into the public system or for use at the premises. They can be fitted on flat roofs or on sloping roofs and can even be constructed as solar roofs with a roof pitch. Solar collector systems are used to harness solar radiation to heat water. The installation of both these types of panels often requires additional components and makes it necessary to pierce the roof skin. The effectiveness of such panels depends on the location, the orientation, the degree of angle of the modules, and any elements in the close vicinity that may cast a shadow. In Germany, the optimum degree of angle of photovoltaic modules is about 30° to 35° facing south for peak loads; when it is intended to cover an even, basic load, a shallower pitch facing east/west is recommended. Regarding the orientation of solar collectors for heating water, it is important to establish the purpose for which the warm water is going to be used, i.e., for providing space heating during the winter months or as domestic hot water throughout the year. In Germany, a 40° to 50° angle and orientation towards the south is recommended for use throughout the year. On flat roofs it is possible to install collectors or panels on a support structure, which may be fixed to the roof or held in place by means of imposed weight. Either way, the additional load has to be taken into account in the structural calculations. Regarding the layout of the modules, it is important to ensure that there is adequate space between them in order to prevent shadowing and, where appropriate, to allow access for the purpose of maintenance. Where panels or collectors are installed on a green roof, care must be taken to prevent plant growth casting unwanted shadows. There should also be a connection to the lightning protection system. > Chapter Lightning protection In the case of sloping roofs, the systems can be fitted to the roof covering, integrated within the covering, or can replace the covering completely. Where the panels are used to replace the roof covering, a water­ proof layer must be fitted beneath the panels. Fastening systems and penetrations must be in accordance with manufacturers’ instructions and have to be sealed appropriately. When panels are fitted on top of the roofing, a distance of at least 6 cm must be maintained to ensure ventilation. Where collectors or modules are fitted as a replacement to parts of the roof covering, they are treated in a similar way to roof windows, with appropriate flashing around the edges. > Fig. 57

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Generally speaking, the installation of photovoltaic systems requires extra care regarding fire safety, not only because the electricity generated can make it easier for fires to start/spread, but also because extinguishing work is made more difficult unless appropriate safety devices are in place.

Sloping roof – PV system fitted above the roofing layer

Sloping roof – PV system as part of the roofing layer

Flat roof – self-supporting PV system on an extensive green roof

Flat roof – PV system on membrane roof with fixed installation

GSPublisherVersion 73.78.81.100

Fig. 57: Installation of photovoltaic systems on sloping and flat roofs

GSPublisherVersion 73.78.81.100

64

In conclusion The preceding chapters have introduced various roof forms, materials, and designs. This book confines itself to simple forms, but it soon becomes clear that there is no such thing as a standard roof; so many different combinations are possible. The architect has to design the type and dimensions of the roofing layers as well as all edge, connection, and penetration details. In particular, the following points should be considered: Roof style: —— Is the selected roof style, including any dormers, permissible ­under the building code? —— Can the roof be accessed? —— Does the selected roof design suit the size and layout of the floor plan? —— Do the selected materials suit the overall appearance of the ­building and its surroundings? Functional aspects: —— Does the attic space have adequate daylight and ventilation? —— Is the thermal insulation of all external surfaces of the building adequate (gables, dormers, exposed parts of the roof, exposed pipes)? —— Does the roof insulation form a continuous layer with the thermal insulation of the adjoining building components (walls, balconies, etc.)? —— Is the roof reliably rainproof? —— Is it possible for any interstitial condensation in building components to escape to the outside? —— Is it possible for rainwater from all roof surfaces to discharge ­without obstruction? —— Is the roof windtight? —— Is the detailing adequate to prevent the formation of condensate (e.g., at penetration points)? —— Is the penetration of humidity from the interior into the building fabric, in particular the insulation, reliably prevented at all points? Even though there are many traditional roof styles, there is great scope for innovative designs. New interpretations of familiar building components can result in exciting features, whilst a focus on the essentials tends to result in a more timeless aesthetic.

65

Despite all the standards and regulations governing the design of a building, the architect should first of all develop a conceptual design for the roof that suits the overall appearance; further detailing will then take place in a second step.

66

Appendix LITERATURE

Bert Bielefeld (ed .): Basics Building Construction, Birkhauser, Basel 2015 Andrea Deplazes: Constructing Architecture – Materials Processes Structures. A Handbook, 5th extended edition, Birkhauser, ­Basel 2018 lnformationsZentrum Beton GmbH: “Well Roofed: The Solid Concrete Roof” (date of retrieval 24.09.2019) Eberhard Schnuck / Hans Jochen Oster / Rainer Barthel / Kurt Kiessl: Roof Construction Manual: Pitched Roofs, Birkhauser, Basel 2003 Klaus Sedlbauer / Eberhard Schnuck / Rainer Barthel / Hartwig M. Kunzel: Flat Roof Construction Manual: Materials, Design, ­Applications, Birkhauser, Basel 2010 Andrew Watts: Modern Construction Envelopes: Systems for archi­ tectural design and prototyping, Birkhauser, Basel 2019

67

STANDARDS Construction DIN EN 1991-1-1

Einwirkungen auf Tragwerke – Teil 1-1: Allgemeine Einwirkungen auf Tragwerke – Wichten, Eigengewicht und Nutzlasten im Hochbau (Actions on structures – Part 1-1: General actions – Densities, self-weight, ­imposed loads for buildings)

DIN EN 1991-1-2

Einwirkungen auf Tragwerke – Teil 1-2: Allgemeine Einwirkungen – Brandeinwirkungen auf Tragwerke (Actions on structures – Part 1-2: General actions – Actions on structures exposed to fire)

DIN EN 1991-1-3

Einwirkungen auf Tragwerke – Teil 1-3: Allgemeine Einwirkungen – Schneelasten (Actions on structures – Part 1-3: General actions – Snow loads)

DIN EN 1991-1-4

Einwirkungen auf Tragwerke – Teil 1-4: Allgemeine Einwirkungen – Windlasten (Actions on structures – Part 1-4: General actions – Wind loads)

DIN EN 1993-1-1

Bemessung und Konstruktion von Stahlbauten – Teil 1-1: Allgemeine Bemessungsregeln und Regeln für den Hochbau (Design of steel ­structures – Part 1-1: General rules and rules for buildings)

DIN EN 1993-1-2

Bemessung und Konstruktion von Stahlbauten – Teil 1-2: Allgemeine Regeln – Tragwerksbemessung für den Brandfall (Design of steel ­structures – Part 1-2: General rules – Structural fire design)

DIN EN 1995-1-1

Bemessung und Konstruktion von Holzbauten – Teil 1-1: Allgemeines – Allgemeine Regeln und Regeln für den Hochbau (Design of timber structures – Part 1-1: General – Common rules and rules for buildings)

DIN EN 1995-1-2

Bemessung und Konstruktion von Holzbauten – Teil 1-2: Allgemeine ­Regeln – Tragwerksbemessung für den Brandfall (Design of timber ­structures – Part 1-2: General rules – Structural fire design)

DIN 1052-10

Herstellung und Ausführung von Holzbauwerken – Teil 10: Ergänzende Bestimmungen (Design, calculation, and dimensioning of timber buildings – Part 10: Additional regulations)

DIN 1045

Tragwerke aus Beton, Stahlbeton und Spannbeton (Concrete and ­reinforced concrete structures: design and construction)

Roof covering DIN EN 490

Dach- und Formsteine aus Beton für Dächer und Wandbekleidungen – Produktspezifikationen (Concrete roofing tiles and fittings for roof covering and wall cladding – Product specifications)

DIN EN 491

Dach- und Formsteine aus Beton für Dächer und Wandbekleidungen – Prüfverfahren (Concrete roofing tiles and fittings for roof covering and wall cladding – Test methods)

DIN EN 492

Faserzement-Dachplatten und dazu gehörende Formteile – Produkt­ spezifikationen und Prüfverfahren (Fibre-cement slates and fittings – Product specification and test methods

DIN EN 501

Dacheindeckungsprodukte aus Metallblech – Festlegung für vollflächig unterstützte Bedachungselemente aus Zinkblech (Roofing products from metal sheet – Specification for fully supported roofing products from zinc sheet)

DIN EN 502

Dacheindeckungsprodukte aus Metallblech – Spezifikation für vollflächig unterstützte Dachdeckungsprodukte aus nichtrostendem Stahlblech (Roofing products from metal sheet – Specification for fully supported roofing products from stainless steel sheet)

68

DIN EN 538

Tondachziegel für überlappende Verlegung – Prüfung der Biegetragfähigkeit (Clay roofing tiles for discontinuous laying – Flexural strength test)

DIN EN 539-1

Dachziegel für überlappende Verlegung – Bestimmung der physikalischen Eigenschaften – Teil 1: Prüfung der Wasserundurchlässigkeit (Clay roofing tiles for discontinuous laying – Determination of physical characteristics – Part 1: Impermeability test)

DIN EN 539-2

Dachziegel für überdeckende Verlegung – Bestimmung der physikalischen Eigenschaften – Teil 2: Prüfung der Frostwiderstandsfähigkeit (Clay roofing tiles for discontinuous laying – Determination of physical characteristics – Part 2: Frost resistance test)

DIN EN 1024

Tondachziegel für überlappende Verlegung – Bestimmung der geo­ metrischen Kennwerte (Clay roofing tiles for discontinuous laying – ­Determination of geometric characteristics)

Din EN 1304

Dachziegel und Formziegel – Begriffe und Produktanforderungen (Clay roofing tiles and fittings – Product definitions and specifications)

DIN EN 12326

Schiefer und Naturstein für überlappende Dachdeckungen und ­Außenwandbekleidungen (Slate and stone for discontinuous roofing and ­external cladding)

FLL Dachbe­ grünungen

Richtlinie für Planung, Bau und Instandhaltung von Dachbegrünungen (Dachbegrünungsrichtlinie) (Guideline for the design, construction, and maintenance of green roofs)

Waterproofing DIN 18531

Abdichtung von Dächern sowie von Balkonen, Loggien und Lauben­ gängen (Waterproofing of roofs, balconies, and walkways)

DIN 18195

Abdichtung von Bauwerken (Waterproofing of buildings)

DIN EN 495

Abdichtungsbahnen (Flexible sheets for waterproofing)

DIN EN 1107

Abdichtungsbahnen – Bestimmung der Maßhaltigkeit (Flexible sheets for waterproofing – Determination of dimensional stability)

DIN EN 1108

Abdichtungsbahnen – Bitumenbahnen für Dachabdichtungen (Flexible sheets for waterproofing – Bitumen sheets for roof waterproofing)

DIN EN 13859

Abdichtungsbahnen – Definitionen und Eigenschaften von Unterdeckund Unterspannbahnen (Flexible sheets for waterproofing – Definitions and characteristics of underlays) Fachregeln für Abdichtungen – Flachdachrichtlinie (Waterproofing rules – Flat roof guideline)

Insulation DIN 4108

Wärmeschutz und Energie-Einsparung in Gebäuden. Beiblatt 2, Wärmebrücken – Planungs- und Ausführungsbeispiele (Thermal insulation and energy economy in buildings – Supplementary sheet 2, thermal bridges – Examples for design and execution)

DIN 4108-2

Wärmeschutz und Energie-Einsparung in Gebäuden – Teil 2: Mindestanforderungen an den Wärmeschutz (Thermal insulation and energy economy in buildings – Part 2: Minimum requirements for thermal insulation)

DIN 4108-3

Wärmeschutz und Energie-Einsparung in Gebäuden – Teil 3: Klima­ bedingter Feuchteschutz – Anforderungen, Berechnungsverfahren und Hinweise für Planung und Ausführung (Thermal insulation and energy economy in buildings – Part 3: Protection against moisture subject to climate conditions – Requirements, calculation methods and directions for design and construction)

69

DIN 4108-4

Wärmeschutz und Energie-Einsparung in Gebäuden -– Teil 4: Wärmeund feuchteschutztechnische Bemessungswerte (Thermal insulation and energy economy in buildings – Part 4: Hygrothermal design values)

DIN V 4108-6

Wärmeschutz und Energie-Einsparung in Gebäuden – Teil 6: Berechnung des Jahresheizwärme- und des Jahresheizenergiebedarfs (Thermal insulation and energy economy in buildings – Part 6: Calculation of annual heat and energy use)

DIN 4108-7

Wärmeschutz und Energie-Einsparung in Gebäuden – Teil 7: Luftdichtheit von Gebäuden – Anforderungen, Planungs- und Ausführungsempfeh­ lungen sowie –beispiele (Thermal insulation and energy economy in buildings – Part 7: Air tightness of buildings – Requirements, recommendations and examples for design and performance)

EnEV

Verordnung über energiesparenden Wärmeschutz und energiesparende Anlagentechnik bei Gebäuden (Directive on energy-conserving thermal insulation and installations in buildings)

Fire safety DIN EN 12101-2

Rauch- und Wärmefreihaltung – Teil 2: Natürliche Rauch- und Wärme­ abzugsgeräte (Smoke and heat control systems – Part 2: Natural smoke and heat exhaust ventilators)

DIN EN 1365

Feuerwiderstandsprüfungen für tragende Bauteile – Teil 2: Decken und Dächer (Fire resistance tests for loadbearing elements – Part 2: Floors and roofs)

DIN EN 13502-5

Klassifizierung von Bauprodukten und Bauarten zu ihrem Brandver­ halten – Teil 5: Klassifizierung mit den Ergebnissen aus Prüfungen von Bedachungen bei Beanspruchung durch Feuer von außen (Fire behaviour ­classification of building products and building methods – Part 5: Classification with the results of tests of roofs exposed to fire from outside)

DIN CEN/TS 1187

Prüfverfahren zur Beanspruchung von Bedachungen durch Feuer von außen (Test methods for external fire exposure to roofs)

DIN 18234

Baulicher Brandschutz großflächiger Dächer – Brandbeanspruchung von unten Teile 1–4 (Fire safety of large roofs for buildings – Fire exposure from below – Parts 1 to 4)

DIN 4102-7

Brandverhalten von Baustoffen und Bauteilen – Teil 7: Bedachungen – Anforderungen und Prüfungen (Fire behaviour of building materials and building components – Part 7: Roofing; definitions, requirements and testing)

Fall prevention DIN 4426

Einrichtungen zur Instandhaltung baulicher Anlagen – Sicherheitstechnische Anforderungen an Arbeitsplätze und Verkehrswege – Planung und Ausführung (Equipment for building maintenance – Safety requirements for workplaces and accesses – Design and construction)

DIN EN 516

Vorgefertigte Zubehörteile für Dacheindeckungen – Einrichtungen zum Betreten des Daches – Laufstege, Trittflächen und Einzeltritte (Prefabricated accessories for roofing – Installations for roof access – Walkways, treads and steps)

DIN EN 517

Vorgefertigte Zubehörteile für Dacheindeckungen – Sicherheitsdachhaken (Prefabricated accessories for roofing – Roof safety hooks)

DIN EN 795

Persönliche Arbeitsschutzausrüstung – Anschlageinrichtungen (Personal fall protection equipment – Anchor devices)

DIN EN 13374

Temporäre Seitenschutzsysteme (Temporary edge protection systems)

DIN EN 17235

Entwurf: Permanente Anschlageinrichtungen und Sicherheitsdachhaken (Design: Permanent anchor devices and safety hooks)

70

Drainage DIN 1986-100

Entwässerungsanlagen für Gebäude und Grundstücke – Teil 100: ­ e­stimmungen in Verbindung mit DIN EN 752 und DIN EN 12056 B (Drainage ­systems on private ground – Part 100: Specifications in ­relation to DIN EN 752 and DIN EN 12056)

DIN EN 612

Hängedachrinnen, Regenfallrohre außerhalb von Gebäuden und Zubehörteile aus Metall (Eaves gutters with bead stiffened fronts and rainwater downpipes with seamed joints made of metal sheet)

DIN EN 12056-3

Schwerkraftentwässerungsanlagen innerhalb von Gebäuden – Teil 3: Dachentwässerung, Planung und Bemessung (Gravity drainage systems inside buildings – Part 3: Roof drainage, layout and calculation)

ZVDH

Hinweise Merkblatt zur Bemessung von Entwässerungen (Fact sheet on the design of drainage systems)

Other elements DIN EN 1873

Vorgefertigte Zubehörteile für Dachdeckungen – Lichtkuppeln aus ­Kunststoff (Prefabricated accessories for roofing – Individual rooflights of plastics)

71

PICTURE CREDITS

Figures 1, 4, 6, 11, 18, 19, 21, 27, 28, 29, 30, and 31 and Table 1 and 6 with reference to Tanja Brotrück, author of the 1st edition of Roof Construction in the Basics series. Figures 7, 13, 14, 15, 16, 23, and 48: Bert Bielefeld, Dortmund. All other figures by the author.

THE AUTHOR

Ann-Christin Siegemund, B.Sc., architect in Dortmund, Germany.

73

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