BS 5268-7.2:1989 recommends a calculation basis for the permissible clear span for joists for flat roofs and roofs with a slope of up to 10 degrees. The recommendations apply to joists at a maximum spacing of 610 mm centre-to-centre, this being the maximum spacing for which the “load-sharing” assumption may be adopted as described in BS 5268-2. The method of calculation makes no allowance for any contribution of the roof decking to the load resistance of the joists although it is assumed that the decking should be capable of providing lateral load distribution. It does not cover the design of joists 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 recommended in BS 6399-1 and BS 6399-3 are considered.
BS 5268-7.2:1989 is applicable to the species and grades of timber given in BS 5268-2.
