BS 5268-3:2006 covers the design, fabrication and use of trussed rafters for roofs. For the purposes of the standard, trussed rafters are assumed to be made from timber members of the same thickness fastened together by metal plate fasteners or plywood gussets. Trussed rafters usually span between external load-bearing walls without the need for intermediate supports from internal walls, lintels or purlins.
This standard provides recommendations on the strength grades of timber used in the fabrication of rafters and other critical design issues. Guidance on the handling, storage and installation of fabricated rafters is given. Information to be exchanged between the trussed rafter designer and the building designer is also listed.
Guidance is provided on:
- structural analysis methods
- engineering design criteria
- standard bracing arrangements for domestic scale roofs
- performance requirements for roof bracing
- production requirements for truss manufacture
- truss handling, storage and erection
- design by testing.
Based on extensive tests, the maximum spans for two common truss configurations for a range of member sizes and roof pitches are given.
