Surveyors span tables for designing roof rafters.
Flat roof timber joist sizes.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.
All the figures are based on the normal loading conditions.
Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists size of roof joist 400mm 450mm 600mm 47 x 97 1 84 1 81 1 74.
For pitched roofs flat roofs and ceiling joists.
A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space.
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.
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.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
Subject ceilings and flat roofs timber sizes and construction details 09 issued 01 04 13 rev page 1 of 2 the following tables give details of the allowable spans and spacing for some of the more common timber sizes used in ceiling and flat roof construction.