- Home
- Members Area
- 1 Welcome
- 2 Introduction
- 3 General
- 3.1 Concrete and its reinforcement
- 3.1.1 Compliance
- 3.1.2 Provision of information
- 3.1.3 Storage of materials
- 3.1.4 Site-mixed concrete
- 3.1.5 Ready-mixed concrete
- 3.1.6 Concrete specification
- 3.1.7 Admixtures
- 3.1.8 Special types of concrete
- 3.1.9 Design of reinforced concrete
- 3.1.10 Installation of reinforcement
- 3.1.11 Blinding concrete
- 3.1.12 Formwork
- 3.1.13 Before concreting
- 3.1.14 Casting
- 3.1.15 Curing
- 3.1.16 Testing
- 3.1.17 Glossary
- 3.2 Cold weather working
- 3.3 Timber preservation (natural solid timber)
- 3.1 Concrete and its reinforcement
- 4 Foundations
- 4.1 Land quality – managing ground conditions
- 4.1.1 Compliance
- 4.1.2 Initial Assessment – desk study (all sites)
- 4.1.3 Initial Assessment – walkover survey (all sites)
- 4.1.4 Initial Assessment – results
- 4.1.5 Basic Investigation (sites where hazards are not identified or suspected)
- 4.1.6 Detailed Investigation (sites where hazards are identified or suspected)
- 4.1.7 Managing the risks (sites where hazards are found)
- 4.1.8 Unforeseen hazards
- 4.1.9 Documentation and verification
- 4.1.10 Guidance for investigations
- 4.1.11 Further information
- 4.2 Building near trees
- 4.2.1 Compliance
- 4.2.2 Provision of information
- 4.2.3 Building near trees
- 4.2.4 The effects of trees on shrinkable soils
- 4.2.5 Foundations in all soil types
- 4.2.6 Excavation of foundations
- 4.2.7 Foundations in shrinkable soils
- 4.2.8 Design and construction of foundations in shrinkable soils
- 4.2.9 Foundation depths for specific conditions in shrinkable soils
- 4.2.10 Heave precautions
- 4.2.11 New drainage
- 4.2.12 Foundation depth charts
- 4.2.13 Foundation depth tables
- 4.2.14 Example
- 4.2.15 Further information
- 4.3 Strip and trench fill foundations
- 4.3.1 Compliance
- 4.3.2 Provision of information
- 4.3.3 Ground conditions
- 4.3.4 Hazardous ground
- 4.3.5 Setting out
- 4.3.6 Services and drainage
- 4.3.7 Safe transmission of loads
- 4.3.8 Sloping ground and stepped foundations
- 4.3.9 Excavations
- 4.3.10 Reinforcement
- 4.3.11 Concrete
- 4.3.12 Movement joints
- 4.3.13 Construction joints
- 4.4 Raft, pile, pier and beam foundations
- 4.4.1 Compliance
- 4.4.2 Provision of information
- 4.4.3 Site conditions
- 4.4.4 Hazardous ground
- 4.4.5 Services and drainage
- 4.4.6 Safe transmission of loads
- 4.4.7 Construction
- 4.4.8 Engineer checks
- 4.4.9 Compressible materials
- 4.4.10 Reinforcement
- 4.4.11 Concrete
- 4.4.12 Movement joints
- 4.4.13 Resistance to moisture
- 4.5 Vibratory ground improvement techniques
- 4.5.1 Compliance
- 4.5.2 Hazardous sites and ground hazards
- 4.5.3 Desk study and site investigation
- 4.5.4 Confirmation of suitability for treatment
- 4.5.5 Suitability of ground conditions
- 4.5.6 Compatibility of the ground, design and treatment
- 4.5.7 Acceptable methods
- 4.5.8 Materials for use as fill
- 4.5.9 Granular material
- 4.5.10 Sitework
- 4.5.11 Adjacent excavations
- 4.5.12 Verification of completed treatment
- 4.1 Land quality – managing ground conditions
- 5 Substructure, Ground Floors, Drainage and Basements
- 5.1 Substructure and ground bearing floors
- 5.1.1 Compliance
- 5.1.2 Provision of information
- 5.1.3 Transfer of loads
- 5.1.4 Ground conditions
- 5.1.5 Services and drainage
- 5.1.6 Ground below fill
- 5.1.7 Fill below floors
- 5.1.8 Infill up to 600mm deep
- 5.1.9 Materials used for fill
- 5.1.10 Harmful or toxic materials
- 5.1.11 Regulatory solutions
- 5.1.12 Walls below the DPC
- 5.1.13 Durability
- 5.1.14 Mortar
- 5.1.15 Wall ties
- 5.1.16 Blinding
- 5.1.17 Ground floor slab and concrete
- 5.1.18 Laying the ground-bearing floor slab
- 5.1.19 Damp proof course
- 5.1.20 Damp proofing concrete floors
- 5.1.21 Thermal insulation
- 5.1.22 Installation of insulation
- 5.1.23 Further information
- 5.2 Suspended ground floors
- 5.2.1 Compliance
- 5.2.2 Provision of information
- 5.2.3 Contaminants
- 5.2.4 Proprietary systems
- 5.2.5 Transfer of loads: concrete floors
- 5.2.6 Reinforced concrete
- 5.2.7 Construction of suspended concrete ground floors
- 5.2.8 Transfer of loads: timber floors
- 5.2.9 Thermal insulation and cold bridging
- 5.2.10 Damp-proofing and ventilation
- 5.2.11 Floor finishes
- 5.2.12 Floor decking
- 5.3 Drainage below ground
- 5.3.1 Compliance
- 5.3.2 Provision of information
- 5.3.3 Preliminary work
- 5.3.4 Foul and surface water disposal
- 5.3.5 Drainage system performance
- 5.3.6 Ground water drainage
- 5.3.7 Design to avoid damage and blockages
- 5.3.8 Durability
- 5.3.9 Septic tanks and cesspools
- 5.3.10 Septic tanks
- 5.3.11 Surface water soakaways
- 5.3.12 Component requirements
- 5.3.13 Excavation
- 5.3.14 Protection of pipework
- 5.3.15 Laying pipework
- 5.3.16 Protection of work
- 5.3.17 Testing
- 5.4 Waterproofing of basements and other below ground structures
- 5.1 Substructure and ground bearing floors
- 6 Superstructure (excluding roofs)
- 6.1 External masonry walls
- 6.1.1 Compliance
- 6.1.2 Provision of information
- 6.1.3 Structural design
- 6.1.4 Fire resistance
- 6.1.5 Acoustic resistance
- 6.1.6 Exposure
- 6.1.7 Thermal insulation
- 6.1.8 Concrete blocks
- 6.1.9 Bricks
- 6.1.10 Stone masonry
- 6.1.11 Construction of masonry walls
- 6.1.12 Lintels
- 6.1.13 Materials suitable for mortar
- 6.1.14 Mortar
- 6.1.15 Render
- 6.1.16 Cladding
- 6.1.17 DPCs and cavity trays
- 6.1.18 Wall ties
- 6.1.19 Handling materials
- 6.1.20 Cold weather working
- 6.2 External timber framed walls
- 6.2.1 Compliance
- 6.2.2 Provision of information
- 6.2.3 Design and certification
- 6.2.4 Load-bearing walls
- 6.2.5 Fixing the frame
- 6.2.6 Nails and staples
- 6.2.7 Sheathing
- 6.2.8 Differential movement
- 6.2.9 Fire resistance
- 6.2.10 Protection from moisture
- 6.2.11 Timber preservation
- 6.2.12 Vapour control layers
- 6.2.13 Breather membranes
- 6.2.14 Wall ties and fixings
- 6.2.15 Insulation
- 6.3 Internal walls
- 6.3.1 Compliance
- 6.3.2 Provision of information
- 6.3.3 Supporting load-bearing internal walls
- 6.3.4 Masonry walls
- 6.3.5 Load-bearing timber walls
- 6.3.6 Fire resistance
- 6.3.7 Sound insulation
- 6.3.8 Partitions: internal non load-bearing
- 6.3.9 Construction of timber partitions
- 6.3.10 Plasterboard
- 6.3.11 Construction of proprietary systems
- 6.3.12 Damp-proof courses
- 6.3.13 Components
- 6.4 Timber and concrete upper floors
- 6.4.1 Compliance
- 6.4.2 Provision of information
- 6.4.3 Upper floor design
- 6.4.4 Fire spread
- 6.4.5 Sound insulation
- 6.4.6 In-situ concrete floors and concreting
- 6.4.7 Precast concrete
- 6.4.8 Timber joist spans
- 6.4.9 Timber joists
- 6.4.10 Construction of timber floors
- 6.4.11 Joists supported by intermediate walls
- 6.4.12 Joists connected to steel
- 6.4.13 Joists into hangers
- 6.4.14 Timber joist and restraint strap
- 6.4.15 Strutting
- 6.4.16 Joists and openings
- 6.4.17 Multiple joists
- 6.4.18 Notching and drilling
- 6.4.19 Floor decking
- 6.4.20 Floating floors or floors between homes
- 6.5 Steelwork
- 6.6 Staircases
- 6.6.1 Compliance
- 6.6.2 Provision of information
- 6.6.3 Fire precautions
- 6.6.4 Lighting
- 6.6.5 Safe transmission of loads
- 6.6.6 Headroom and width
- 6.6.7 Design of steps
- 6.6.8 Landings
- 6.6.9 Guarding
- 6.6.10 Handrails
- 6.6.11 Timber staircases
- 6.6.12 Timber and wood-based products
- 6.6.13 Finished joinery
- 6.6.14 Concrete staircases
- 6.6.15 Steel staircases
- 6.6.16 Staircase units
- 6.6.17 Fixings
- 6.6.18 Protection
- 6.7 Doors, windows and glazing
- 6.8 Fireplaces, chimneys and flues
- 6.8.1 Compliance
- 6.8.2 Provision of information
- 6.8.3 Solid fuel – fireplaces and hearths
- 6.8.4 Solid fuel – combustion air
- 6.8.5 Solid fuel – flue pipes
- 6.8.6 Solid fuel – Chimneys
- 6.8.7 Solid fuel – outlets and terminals
- 6.8.8 Gas – fireplaces and hearths
- 6.8.9 Gas – combustion air
- 6.8.10 Gas – flue pipes
- 6.8.11 Gas – chimneys
- 6.8.12 Gas – outlets and terminals
- 6.8.13 Oil – fireplaces and hearths
- 6.8.14 Oil – combustion air
- 6.8.15 Oil – flue pipes
- 6.8.16 Oil – chimneys
- 6.8.17 Oil – outlets and terminals
- 6.8.18 All – fireplaces and hearths
- 6.8.19 All – fireplace surrounds
- 6.8.20 All – flue pipes
- 6.8.21 All – flue liners
- 6.8.22 All – flues
- 6.8.23 All – chimneys
- 6.8.24 Masonry
- 6.8.25 Mortar
- 6.8.26 DPC
- 6.8.27 Flashings
- 6.8.28 Terminals
- 6.8.29 Flue testing
- 6.8.30 Further information
- 6.9 Curtain walling and cladding
- 6.9.1 Compliance
- 6.9.2 Provision of information
- 6.9.3 Certification
- 6.9.4 Loads
- 6.9.5 Support and fixings
- 6.9.6 Durability
- 6.9.7 Interfaces
- 6.9.8 Insulation
- 6.9.9 Damp proofing and vapour control
- 6.9.10 Installation and tolerances
- 6.9.11 Electrical continuity and earth bonding
- 6.9.12 Maintenance
- 6.9.13 Glazing, gaskets and sealants
- 6.9.14 Cavity barriers and firestops
- 6.9.15 Ventilation screens
- 6.9.16 Handling and storage
- 6.9.17 Curtain walling
- 6.9.18 Rainscreen cladding
- 6.9.19 Insulated render and brick slip cladding
- 6.10 Light steel framed walls and floors
- 6.10.1 Compliance
- 6.10.2 Provision of information
- 6.10.3 Certification
- 6.10.4 Load-bearing walls and floors
- 6.10.5 Control of fire
- 6.10.6 Acoustic performance
- 6.10.7 Steel and fixings
- 6.10.8 Detailing of steel joist
- 6.10.9 Restraint
- 6.10.10 Fixing floor decking and ceilings
- 6.10.11 Moisture control
- 6.10.12 Insulation
- 6.10.13 Vapour control layers
- 6.10.14 Breather membranes
- 6.10.15 Construction of load-bearing walls and external infill walls
- 6.10.16 Construction of non load-bearing walls
- 6.10.17 Panels, cladding and boards
- 6.10.18 Wall ties
- 6.10.19 Services
- 6.10.20 Further information
- 6.11 Render
- 6.1 External masonry walls
- 7 Roofs
- 7.1 Flat roofs and balconies
- 7.1.1 Compliance
- 7.1.2 Provision of information
- 7.1.3 Flat roof and balcony design
- 7.1.4 Timber and timber decks
- 7.1.5 Profiled metal decks
- 7.1.6 Concrete decks
- 7.1.7 Thermal insulation and vapour control
- 7.1.8 Waterproofing and surface treatments
- 7.1.9 Green and proprietary roofs
- 7.1.10 Detailing of flat roofs
- 7.1.11 Accessible thresholds
- 7.1.12 Drainage
- 7.1.13 Guarding to balconies
- 7.2 Pitched roofs
- 7.2.1 Compliance
- 7.2.2 Provision of information
- 7.2.3 Design of pitched roofs
- 7.2.4 Protection of trusses
- 7.2.5 Durability
- 7.2.6 Wall plates
- 7.2.7 Joints and connections
- 7.2.8 Restraint
- 7.2.9 Bracing for trussed rafter roofs
- 7.2.10 Strutting for attic trusses and cut roofs that form a floor
- 7.2.11 Support for equipment
- 7.2.12 Access
- 7.2.13 Dormer construction
- 7.2.14 Underlay and sarking
- 7.2.15 Ventilation, vapour control and insulation
- 7.2.16 Firestopping and cavity barriers
- 7.2.17 Battens
- 7.2.18 Roof coverings
- 7.2.19 Fixing tiles and slates
- 7.2.20 Weathering details
- 7.2.21 Valleys and hidden gutters
- 7.2.22 Drainage
- 7.2.23 Fascias and trim
- 7.2.24 Spandrel panels
- 7.1 Flat roofs and balconies
- 8 Services
- 8.1 Internal services
- 8.1.1 Compliance
- 8.1.2 Provision of information
- 8.1.3 Water services and supply
- 8.1.4 Cold water storage
- 8.1.5 Hot water service
- 8.1.6 Soil and waste systems
- 8.1.7 Electrical services and installations
- 8.1.8 Gas service installations
- 8.1.9 Meters
- 8.1.10 Space heating systems
- 8.1.11 Installation
- 8.1.12 Extract ducts
- 8.1.13 Testing and commissioning
- 8.2 Low or zero carbon technologies
- 8.2.1 Compliance
- 8.2.2 Provision of information
- 8.2.3 Clean Air Act
- 8.2.4 System design
- 8.2.5 Access
- 8.2.6 Handling, storage and protection
- 8.2.7 Sequence of work
- 8.2.8 Location
- 8.2.9 Building integration
- 8.2.10 Fixing
- 8.2.11 Electrical installation requirements
- 8.2.12 Pipes, insulation and protection from cold
- 8.2.13 Ground collectors
- 8.2.14 Fuel storage
- 8.2.15 Safe discharge
- 8.2.16 Testing and commissioning
- 8.2.17 Handover requirements
- 8.2.18 Further information
- 8.3 Mechanical ventilation with heat recovery
- 8.1 Internal services
- 9 Finishes
- 10 External works
- 10.1 Garages
- 10.2 Drives, paths and landscaping
- 10.2.1 Compliance
- 10.2.2 Provision of information
- 10.2.3 Stability
- 10.2.4 Freestanding walls and retaining structures
- 10.2.5 Guarding and steps
- 10.2.6 Drives, paths and landscaping
- 10.2.7 Materials
- 10.2.8 Garden areas within 3m of the home
- 10.2.9 Garden areas
- 10.2.10 Timber decking
- 10.2.11 Landscaping
7.2.3Design of pitched roofs
The sizing and spacing of members shall ensure structural stability and provide restraint to the structure without undue movement or distortion. Issues to be taken into account include:
- trussed rafter roofs
- traditional cut roofs.
The design of pitched roofs should:
- have dead and imposed loads calculated in accordance with BS EN 1991-1-1, BS EN 1991-1-3 and BS EN 1991-1-4
- be in accordance with PD 6693-1, and Technical Requirement R5, where appropriate
- be appropriate for the location, accounting for exposure and wind uplift
- ensure that the structure is coherent and that all forces are resolved
- ensure stability with the complete structure, including the connections and compatibility with the supporting structure and adjacent elements
- where trussed rafters and a cut roof are combined, the designer should provide details of the complete roof (particular care is needed in such circumstances).
- the roof is not a basic pitched roof
- hips, valleys or other special features are included in a trussed rafter roof
- the spans, sizes, spacing or strength classes of the timber are outside the scope of authoritative tables
- trussed rafters support traditional cut roof members, or
- it is a proprietary system (designs supplied by manufacturers will generally be acceptable).
- the timber specification should be in accordance with BS EN 1912, or the timber species and strength class identified
- the timber should be marked accordingly.
- installed in accordance with the design, and the structure or spacing should not be altered without prior consent from the designer
- fixed to the wall in accordance with the design (e.g. using double skew nailing or truss clips)
- vertical and suitably located (where necessary, temporary bracing should be used to maintain spacing and to keep trusses vertical)
- evenly spaced at maximum 600mm centres.
- X = distance between centres of trussed trimmed rafters and the adjacent trussed rafter
- A = design spacing of trussed rafters
- B = nominal width of opening.
- designed to be permanently fastened together
- either fixed together during manufacture, or fully detailed drawings and specifications showing the fixing method should be supplied.
- 9.5mm plasterboard should be fixed at a maximum support spacing of 450mm.
- 12.5-15mm plasterboard should be fixed at a maximum support spacing of 600mm.
- Additional members will generally be required to support coverings and finishes where trusses are spaced further apart.
- the design should specify the details of each structural member and the method of fixing or jointing
- the roof should be in accordance with the design and members accurately located
- members should be fully supported and tied together where necessary, particularly where the roof is not a simple triangle
- temporary support to long span members should be used until framing is complete
- purlins and binders should be built in where necessary
- framing should be completed before coverings are installed.
Roofs should be designed by an engineer in accordance with Technical Requirement R5 where:
Structural timber should be of a suitable grade and specified according to the strength classes in BS EN 338, e.g. C16, C24 or TR26. When using the BS 4978 grading rules:
Trussed rafter roofs
Trussed rafters should be:
Where the maximum 600mm spacing cannot be achieved, e.g. to accommodate hatch openings or chimneys, spacing may be increased to a maximum of twice the nominal spacing, provided that the spacing X is less than, or equal to, 2A-B where:
Where multiple and reinforcing timbers to simple or multiple trussed rafters are used, they should be:
Hipped roofs constructed with trussed rafters typically require a series of diminishing mono-pitched trusses supported by a girder truss.
The bearing of mono-pitched trusses into shoes should be in accordance with Table 1, unless designed by an engineer in accordance with Technical Requirement R5.
Table 1: Bearing length of mono-pitched trusses into shoes
Span | Minimum bearing length | Minimum thickness of trussed rafter |
---|---|---|
Less than 4m | 50mm | 35mm |
4m or more | 75mm | 35mm |
Ceiling finishes should be fixed according to the spacing of the support members and the thickness of the sheet. Plasterboard should be fixed as follows:
Where the width of a gable ladder exceeds that of the trussed rafter centres, noggings should be used to reduce the span of the roofing tile battens.
Traditional cut roofs
For traditional cut roofs:
Table 2: Basic timber members
Member | Notes |
---|---|
Valley rafter | Provides support for loads from both sections of the roof and should: ■ be larger than ordinary rafters to take the additional load ■ provide full bearing for the splay cut of jack rafters ■ be provided with intermediate support where required. |
Hip rafter | Provides spacing and fixing for jack rafters and should: ■ have a deeper section than the other rafters to take the top cut of the jack rafters. Purlins should be mitred at hips and lip cut to accept the bottom of the hip rafter. |
Ceiling joist or ties | Provides support for the rafters and should: ■ stop the walls and roof spreading outwards ■ provide support to the ceiling finish and walkways, etc. |
Ridge | Provides fixings and spacing for the tops of the rafters. |
Purlin | Provides support to long span rafters to prevent deflection and increase stiffness. |
Struts | Provides support to purlins to prevent deflection and to transfer roof loads to the load-bearing structure below. |
Collar | Ties the roof together at purlin level. |
Ceiling binders and hangers | Provides support to long span ceiling joists. |
Pole plates | Similar to purlins, but used where ceiling joists are above wall plate level. |
Generally sizes should be as Table 3, unless designed by an engineer in accordance with Technical Requirement R5.
Table 3: Typical sizes for timber members
Member | Minimum size |
---|---|
Struts | 100mm x 50mm |
Valleys | 32mm thick |
Ridges and hips | Rafter cut + 25mm |