Find the column for your dead load and spacing and the row for your timber size to find the permissible clear span in metres.
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.
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.
Surveyors span tables for designing roof rafters.
These spans were calculated using our flat roof joist calculation.
Click on a span to generate a full calculation you can adjust the exact span.
For pitched roofs flat roofs and ceiling joists.
Solid timber joist sizes are provided in the bs 8103 3 span tables.