Principles of pitched roof construction

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There are a number of ways to design and construct pitched roofs using timber. Traditionally, builders constructed them on site, cutting and fitting each piece to its neighbours. Following the Second World War, various forms of prefabricated truss were developed, with the intermediate rafters and purlins cut and fitted on site.

Currently, the highly engineered and slender trussed rafter, where the rafters and ceiling joists are triangulated to form a lightweight prefabricated truss, is the most widely used form of domestic roof construction.

This Wood Information Sheet (WIS) covers the general principles of pitched roof design only. It does not cover the design of hatches, chimney openings or the additional support that is required for water tanks or other added loads.



  • Site-constructed roofs
  • Purlin roofs
  • Bolted and connectored trusses
  • Trussed rafter roofs
  • Rooms in the roof
  • Insulation and ventilation
  • Preservative treatments

Suggested Reading

Trussed raftersnavigation-arrow

Widely used for a range of building types, trussed rafters are an economical, versatile and straightforward solution to providing a roof to a building.

Trussed rafters are individually designed prefabricated structural components made from strength-graded timber members of the same thickness, joined together with punched metal plate connectors....

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Creating roofscapes with trussed raftersnavigation-arrow

Trussed Rafters have become part of the modern building vocabulary. Around 95% of all new house roofs are constructed using trussed rafters as are an increasing proportion of roofs for nondomestic premises such as offices, retail outlets, hospital extensions, leisure developments etc.

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Guidelines for the storage and erection of trussed rafters on site (Part 1).navigation-arrow

When a delivery of trussed rafters arrives on site the contractor(s) involved should be prepared and have already allocated sufficient and suitable resources to ensure the trussed rafters are unloaded safely and in a manner so as not to overstress or damage the trusses.

This information sheet gives a...

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