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


This Wood Information Sheet was reviewed in September 2021 and minor amendments were made including the addition of a new section on panel roofs.


For queries about this technical document, please get in touch with its authors via BM TRADA’s Technical Helpline on +44 (0)1494 569601 or email


A paper/digital copy of this Wood Information Sheet is available in the BM TRADA Bookshop, which also hosts additional specialist timber publications.

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