Timber Roof Joist Sizes

Bs 5268 7 1 was published before bs 6399 1.

Timber roof joist sizes. Surveyors and structural engineers use data from tables below to help calculate the size of timbers necessary to give adequate support to timber floors. And the row for your timber size to find the permissible clear span in metres. 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. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction.

Greater than 2400 mm and 3 6 kn load per metre width of floor for spans less than 2400 mm to ensure that very small joist sizes do not result from the calculations for smaller spans. Flat roof joists rafters purlin. This is the distance between joist centres. These tables can help calculate whether floor joists are strong enough to support themselves and the load they carry without the help of any walls underneath.

These span tables apply only to flat roof and roof with a slope of up to 10 degrees. The lengths and sizes of joists vary depending on the species and quality of the lumber used. All the figures are based on roofing tiles or slates laid on timber laths over sarking felt. For pitched roofs flat roofs and ceiling joists.

For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine. Pitched roof timber sizes. Surveyors span tables for designing roof rafters. Rafter and joist span faq.

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 47 x 120 2 43 2 39 2 27 47 x 145 3 08 3 02 2 87 47 x 170 3 75 3 67 3 42 47 x 195 4 41 4 31 3 92 47 x 220 5 04 4 85 4 41 75 x 170 4 50 4 38 3 99. Solid timber joist sizes are provided in the bs 8103 3 span tables. 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. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.

Timber floor joists shall be adequate for the spans and loads and be correctly installed.