The following span tables are indicative of some of the spans required for domestic floor joists where c16 and c24 strength classes are used.
C24 flat roof joist span.
Joists under each partition.
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.
Click here to download c16 span table leaflet c24 span table our premium grade of carcassing is c24 graded.
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 4 41 170 x 75 4 50 4.
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.
They refer to a dead load of not more than 0 5kn m 2 excluding the weight of the joist and an imposed load not exceeding 1 5 kn m 2.
Clear spans for flat roof joists in metres.
Timber floor joists shall be adequate for the spans and loads and be correctly installed.
For pitched roofs flat roofs and ceiling joists.
Maximum clear span of flat roof joists in metres for sc3 timber spacing between joists 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 4 38.
Timber to be covered these span tables do not apply to timber which is fully exposed to the elements.
Span tables for flat roof joists to bs 5268 7 2 imposed loads of 0 75 kn m for maintenance and snow load are applicable where there is no permanent access no fixed ladder or staircase and most areas where the altitude does not exceed 100 metres refer to bs 6399 3.
These span tables apply only to flat roof and roof with a slope of up to 10 degrees.
Solid timber joist sizes are provided in the bs 8103 3 span tables.
Size of roof joists spacing of joists.
Stocked at all branches click here to download c24 strength class pdf document.
C16 span table only stocked at our mitcham depot.
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.
