Roof Timber Sizes And Spans

Pitched roof timber sizes.

Roof timber sizes and spans.

For pitched roofs flat roofs and ceiling joists. Ceiling joist span use this table to determine the maximum lengths of ceiling joists based on species of lumber joist spacing and joist size. Rafter spans can be extended slightly beyond what the rafter tables suggest when there is a cantelever extending beyond the supporting wall. 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.

For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements. Find the column for your dead load and spacing and the row for your timber size to find the permissible clear span in metres. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in flat roof construction.

All the figures are based on roofing tiles or slates laid on timber laths over sarking felt. These spans were calculated using our flat roof joist calculation. All figures are based on normal loading conditions found in domestic construction. Click on a span to generate a full calculation you can adjust the exact span.

Maximum rafter spans for a patio roof in areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot.