Timber Roof Purlin Span Tables

All the figures are based on roofing tiles or slates laid on timber laths over sarking felt.

Timber roof purlin span tables. Pergola rafter spans for 600 mm and 900 mm spacing. 2 for design parameters refer to figure 7 26. Wind classification n1 n2. Span tables for flat roof joists to bs 5268 7 2 imposed loads of 0 75 kn m for maintenance and snow load are applicable where there is no permanent access no fixed ladder or staircase and most areas where the altitude does not exceed 100 metres refer to bs 6399 3.

Roof load width rlw and floor load width flw can be determined from as1684 or from the images below. As per as1684 and as4055 spanman adopts a nett pressure coefficient applied along the full length of the purlin of cpn 2 0 for non cyclonic zones n1 to n6 and cpn 2 5 for cyclonic zones c1 to c4. Spacing should be interpreted as the centre to centre distance between adjacent parallel members. 1 refer to general notes for information that is relevant for all span tables.

3 where rafters are equal to or exceed four times their breath blocking should be used to reduce distortion. For pitched roofs flat roofs and ceiling joists. Required size for a given span. Purlins near roof edges or changes of roof slope are subject to higher wind forces than interior purlins.

Maximum clear span of purlins in metres for roof pitches of between 30 and 45 degrees.