Flat Roof Joist Sizes Building Regs

The size of your joists and noggins and preliminary timber layer will be determined by the weight of your flat roof.

Flat roof joist sizes building regs.

Solid timber joist sizes are provided in the bs 8103 3 span tables. Sizes of joists needed for flat roof construction. 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. Surveyors span tables for designing roof rafters.

So any timber joists that are used need to be strong enough to support this weight. 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. 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. 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.

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. Make sure your comply with flat roof building regulations. Old asbestos roofs are often replaced with flat roofs. Timber floor joists shall be adequate for the spans and loads and be correctly installed.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. 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. 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. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc.

Ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice. Supporting imposed load. For pitched roofs flat roofs and ceiling joists.