Standard Flat Roof Joist Sizes

This demo version is fixed at 1m clear span.

Standard flat roof joist sizes.

Supporting imposed load. The full version allows any 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. Rafter and joist span faq.

Code of practice for permissible stress design materials and workmanship and bs 5268 7 2 1989 structural use of timber section 7 2. 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. 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. The lengths and sizes of joists vary depending on the species and quality of the lumber used.

The range of joist sizes used in homes varies though between 2 by 4 inches and 2 by 12 inches. Surveyors span tables for designing roof rafters. But they do tend to space rafters in one of several industry standard increments typically. 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.

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. 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. 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. For pitched roofs flat roofs and ceiling joists.

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. Enter a specific joist size 2 loadings dead load. Boarding to be fastened on top of flat roof joists with a depth to width ratio greater than 4 the allowable clear spans have been calculated in accordance with bs 5268 2 2002 structural use of timber part 2. The difference in the joist sizes applies to the width of the boards which determines the height of the.

Builders aren t bound by standard rafter spacing measurements.