Timber Roof Purlin Span Tables

All the figures are based on roofing tiles or slates laid on timber laths over sarking felt. 1 refer to general notes for information that is relevant for all span tables. Wind classification n1 n2.

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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.

Timber roof purlin span tables.

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

Pergola rafter spans for 600 mm and 900 mm spacing. Spacing should be interpreted as the centre to centre distance between adjacent parallel members. Surveyors and structural engineers utilise data from tables below to help calculate the correct size strength and centres of roof timbers for the required spans and loadings. Purlins near roof edges or changes of roof slope are subject to higher wind forces than interior purlins.

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. Roof load width rlw and floor load width flw can be determined from as1684 or from the images below. Required size for a given span. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction.

2 for design parameters refer to figure 7 26.