Roof Timber 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.

Roof timber span tables.

Technical diagram on page 35 30mm m aximum allow able sp ans mm sheet roof spacing mm rafter size 600 760 900 1000 1200 66 x 30 850 750 700 700 600 90 x 30 1200 1050. Surveyors span tables for designing roof rafters. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. For pitched roofs flat roofs and ceiling joists.

Roof load width rlw and floor load width flw can be determined from as1684 or from the images below. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction. Span tables f7 rafters a maximum roof pitch of 25 degrees is assumed. All the figures are based on roofing tiles or slates laid on timber laths over sarking felt.

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. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. Also available for the android os. Roof rafter span use this table to determine the maximum lengths of roof rafters based on species and grade of lumber spacing dimensions load and slope.

Required size for a given span. Other more complex load condition spans can be determined with our free hyne timber design 7 5 software. Span calculator for wood joists and rafters also available for the android os. Construction details should be in accordance with as1684 2.

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. 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. Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support. Pitched roof timber sizes.

Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size.