Flat Roof Joist Sizes Building Regs

Surveyors span tables for designing roof rafters.

Flat roof joist sizes building regs.

Sizes of joists needed for flat roof construction. Solid timber joist sizes are provided in the bs 8103 3 span tables. 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. Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2.

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. Old asbestos roofs are often replaced with flat roofs. Building control guidance note 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. Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall.

Flat roofs on houses must be designed and built to be strong durable and wind resistant. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. So any timber joists that are used need to be strong enough to support this weight. 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 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2.

Timber floor joists shall be adequate for the spans and loads and be correctly installed. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. For pitched roofs flat roofs and ceiling joists. Supporting imposed load.

Make sure your comply with flat roof building regulations. This is an abridged representation of building regulations table a1 click here for structural design calculations spans of timber joists in suspended timber ground floors span tables. 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.