Timber floor joists shall be adequate for the spans and loads and be correctly installed.
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.
This span table is to the format and methodology given in bs 5268 7 2.
Click on a span to generate a full calculation you can adjust the exact span.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
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.
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.
For pitched roofs flat roofs and ceiling joists.
Surveyors span tables for designing roof rafters.
These spans were calculated using our flat roof joist calculation.