Flat Roof Timber Sizes And Spans

For simple construction such as domestic construction this can be determined from span table supplements in as1684 2 and as1684 3.

Flat roof timber sizes and spans.

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. This is the distance between joist centres. For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine. Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support.

Usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size automatically calculate sizes suitable for supporting the loads below. Stress grades and timber sizes combine to determine the spanning ability of load carrying members. 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 05 2 67 3 22 3 77 4 31 4 85 assumptions at 400mm centers supporting permanent load excluding self weight of joists up to 50kg m2. The lengths and sizes of joists vary depending on the species and quality of the lumber used.

Span tables allow users to choose an appropriate size and stress grade to achieve spanning needs. For pitched roofs flat roofs and ceiling joists. These span tables apply only to flat roof and roof with a slope of up to 10 degrees. Supporting imposed load up to 150kg m2.

Surveyors span tables for designing roof rafters. Should refer to trada document span tables for solid timber members in floors ceilings and roofs excluding trussed rafter roofs for dwellings or ask your lbc surveyor for advice.