Flat Roof Joist Sizes And Spans

3 stud construction standard utility.

Flat roof joist sizes and spans.

For pitched roofs flat roofs and ceiling joists. L 720 l 600 l 480 l 360 l 240 l 180. The lengths and sizes of joists vary depending on the species and quality of the lumber used. 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.

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. Floor joists ceiling joists rafters snow load rafters roof live load deflection limit. 1 psf lbf ft2 47 88 n m2. 1 ft 0 3048 m.

Spacing in 12 16 19 2 24. 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. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. Surveyors span tables for designing roof rafters.

This is the distance between joist centres. Usually 400 450 or 600mm but any value can be used up to 610mm max usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size. 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. These span tables apply only to flat roof and roof with a slope of up to 10 degrees.

Live load 20 lbs ft2 956 n m2 maximum span ft in nominal size. 1 in 25 4 mm. 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.