Timber Roof Joist Sizes

These span tables apply only to flat roof and roof with a slope of up to 10 degrees.

Timber roof joist sizes.

Bs 5268 7 1 was published before bs 6399 1. 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. The lengths and sizes of joists vary depending on the species and quality of the lumber used. 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.

Where the tables do not apply or where there are concentrated loads floor joists should be designed by an engineer in accordance with technical requirement r5. Solid timber joist sizes are provided in the bs 8103 3 span tables. 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. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction.

This is the distance between joist centres. Usually 400 450 or 600mm but any value can be used up to 610mm max usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size. Flat roof joists rafters purlin. For pitched roofs flat roofs and ceiling joists.

Rafter and joist span faq. Surveyors span tables for designing roof rafters. Pitched roof timber sizes. 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.

And the row for your timber size to find the permissible clear span in metres. Timber floor joists shall be adequate for the spans and loads and be correctly installed. Surveyors and structural engineers use data from tables below to help calculate the size of timbers necessary to give adequate support to timber floors. 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.

All the figures are based on roofing tiles or slates laid on timber laths over sarking felt.