Timber Roof Span Tables

Span tables allow users to choose an appropriate size and stress grade to achieve spanning needs.

Timber roof span tables.

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. Construction details should be in accordance with as1684 2. A maximum roof pitch of 25 degrees is assumed. 3 where rafters are equal to or exceed four times their breath blocking should be used to reduce distortion.

1 refer to general notes for information that is relevant for all span tables. 2 for design parameters refer to figure 7 26. Joist and rafter span tables. 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.

Wind classification n1 n2. Span tables span tables can be used to determine the size of a timber member of a particular strength class required for a given span. For simple construction such as domestic construction this can be determined from span table supplements in as1684 2 and as1684 3. Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.

Pergola rafter spans for 600 mm and 900 mm spacing. Surveyors span tables for designing roof rafters. You can also use the wood beam calculator from the american wood council website to determine maximum rafter and joist lengths. Other more complex load condition spans can be determined with our free hyne timber design 7 5 software.

Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. Span tables use the span tables below to determine allowable lengths of joists and rafters based on size and standard design loads.