Code of practice for structural use of timber - Part 11: Recommendations for the calculation basis for span tables - Section 4: Domestic rafters
This section of MS 544-11 recommends a calculation basis for the permissible clear span for roof rafter with a slope from 15° to 45°. The recommendations apply to rafters at a maximum spacing of 1 200 mm centre-to-centre. The method of calculation makes no allowance for any contribution of other parts of the roof to the load resistance of the rafters although it is assumed that the tiling battens are capable of providing lateral load distribution and lateral support.
This section does not cover the design of rafters taking account of a structural contribution by sheet material supporting the roofing where such action can be provided by adequate design of its attachments as in a stressed skin panel roof. The uniform and concentrated loads of Uniform Building By-Laws 1984 are considered. This section also covers the overhang calculation. Typical examples of roof construction are given in Figures 1 and 2, and examples of rafters are given in Figure 3.
This section of MS 544-11 is applicable to the species, strength groups and grades of timber given in MS 544: Part 2:2001.
