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.

Roof joist sizes building regs. Size of roof joists spacing of joists 400mm 450mm 600mm 97 x 47 1 84 1 81 1 74 120 x 47 2 43 2 39 2 27 145 x 47 3 08 3 02 2 87 170 x 47 3 75 3 67 3 42 195 x 47 4 41 4 31 3 92 220 x 47 5 04 4 85. 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. Solid timber joist sizes are provided in the bs 8103 3 span tables. 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.

Find the column for your dead load and spacing and the row for your timber size to find the permissible clear span in metres. Surveyors span tables for designing roof rafters. This span table is to the format and methodology given in bs 5268 7 2. 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.

For pitched roofs flat roofs and ceiling joists.