Flat Roof Timber Joist Sizes

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.

Flat roof timber joist sizes.

Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. The lengths and sizes of joists vary depending on the species and quality of the lumber used. 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. Eurocode 5 span tables for solid timber members in floors ceilings and roofs for dwellings 3rd edition.

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. 1 2 timber strength class and joist size automatically calculate sizes suitable for supporting the loads below c16 cost effective for most applications c24 stronger more demanding c14 c18 c22 c27 c30 c35 c40. 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.

Surveyors span tables for designing roof rafters. 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. Should refer to trada document span tables for solid timber members in floors ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. And the row for your timber size to find the permissible clear span in metres.

Bs 5268 7 1 was published before bs 6399 1. Flat roof joists rafters purlin. 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. For timber floors between homes.

Size of joists mm clear span c16 joist m clear span c24 joist m 47 x 95 47 x 120 47 x 145 47 x 170 47 x 195 47 x 220 1 77 2 40 2 89 3 38 3 87 4 36 2 04 2 75 3 47 4 20 4 93 5 66 floor joists flat roof joists assumptions at. The section sizes are based on regularised als or cls timber. Rafter and joist span faq. If supporting lightweight partitions running parallel to joists provide two additional joists under each partition.

Tables 1 and 2 in this chapter are derived from the trada technology ltd. 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.