Standard Flat Roof Joist Sizes

But they do tend to space rafters in one of several industry standard increments typically.

Standard flat roof joist sizes.

1 enter joist details 1 1 span and joist spacing. Supporting imposed load. 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. Though there is no standard joist size for the ceilings in all buildings most average homes use ceiling joists in a board size of 2 by 6 inches.

The range of joist sizes used in homes varies though between 2 by 4 inches and 2 by 12 inches. The full version allows any size. Rafter and roof joist spacing is only one part of a complex roof design that works together to form a structure that meets building codes and can hold up the weight of the roof and roof load. 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 3 99.

Enter a specific joist size 2 loadings dead load. Surveyors span tables for designing roof rafters. Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. 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.

Rafter and joist span faq. Where a new flat roof abuts an existing external wall the joists can be hung on metal joist hangers which are fixed to a horizontal timber plate wall bolted to the wall. Builders aren t bound by standard rafter spacing measurements. 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.

A cavity closer should be provided to the top of the walls to prevent fire spread and to stop damp air entering the roof space. For pitched roofs flat roofs and ceiling joists. Compare click to add item 24 spreadweb residential roof truss 5 12 pitch 87 to the compare list add to list click to add item 24 spreadweb residential roof truss 5 12 pitch 87 to your list sku 1889754. Flat roof joist calculator.

The lengths and sizes of joists vary depending on the species and quality of the lumber used.