Flat Roof Joist Sizes Uk

Sizes of joists needed for flat roof construction.

Flat roof joist sizes uk.

Surveyors span tables for designing roof rafters. 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. 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. Timber floor joists shall be adequate for the spans and loads and be correctly installed.

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. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. The joists will normally be placed at 400mm centres but no more than 600mm centres. Permissible clear span metres.

Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. 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. Flat roof with no permanent access and altitude not exceeding 100m 0 75 kn m udl 0 9 kn point load most areas exceeding 100m but not exceeding 200m excluding parts of scotland pennines north east england refer to bs 6399 3 1 kn m udl 0 9 kn point load. As you may imagine there is a fair amount of weight involved here in terms of boards felt etc.

So any timber joists that are used need to be strong enough to support this weight. Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600. Solid timber joist sizes are provided in the bs 8103 3 span tables.