Timber Roof Joist Sizes

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

Timber roof joist sizes.

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 lengths and sizes of joists vary depending on the species and quality of the lumber used. The following tables give details of the allowable spans and spacing for some of the more common timber sizes used in traditional roofing construction. Surveyors and structural engineers use data from tables below to help calculate the size of timbers necessary to give adequate support to timber floors.

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. 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. Surveyors span tables for designing roof rafters.

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. Bs 5268 7 1 was published before bs 6399 1. Pitched roof timber sizes.

Rafter and joist span faq. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. 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. All the figures are based on roofing tiles or slates laid on timber laths over sarking felt.

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. 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. This is the distance between joist centres. 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.

And the row for your timber size to find the permissible clear span in metres.