Flat Roof Joist Sizes Building Regs

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.

Flat roof joist sizes building regs.

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. Sizes of joists needed for flat roof construction. Flat roofs on houses must be designed and built to be strong durable and wind resistant. The size of your joists and noggins and preliminary timber layer will be determined by the weight of your flat roof.

Surveyors span tables for designing roof rafters. Make sure your comply with flat roof building regulations. Solid timber joist sizes are provided in the bs 8103 3 span tables. Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.

As you may imagine there is a fair amount of weight involved here in terms of boards felt etc. Supporting imposed load. 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. 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.

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. So any timber joists that are used need to be strong enough to support this weight. Timber floor joists shall be adequate for the spans and loads and be correctly installed. 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.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 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.