Roof Joist Sizes Building Regs

For pitched roofs flat roofs and ceiling joists.

Roof joist sizes building regs.

Solid timber joist sizes are provided in the bs 8103 3 span tables. Surveyors span tables for designing roof rafters. This span table is to the format and methodology given in bs 5268 7 2. Timber floor joists shall be adequate for the spans and loads and be correctly installed.

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. Find the column for your dead load and spacing and the row for your timber size to find the permissible clear span in metres. 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. 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 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.