Flat Roof Joist Spacing

Dead load per square metre in kn m supported by joists.

Flat roof joist spacing.

1 ft 0 3048 m. Keep in mind that these are minimums for the spacing indicated you can select larger sizes to handle excessive loads or for appearance. 2 are indicated below. The same concept holds true for roof trusses.

Common spacing for trusses on this type of building is often between 2 and 4 feet but trusses built with advanced designs may allow spacing as great as 8 or 12 feet. This is the distance between joist centres. Spacing in exterior exposure. The sizing and spacing will depend upon the loads imposed on them and the required span.

So the space between rafters can be greater without reducing the maximum span. In other words you would space a roof joist 15 inches apart from another roof joist but never 17 inches apart. If the roof is not completely square you can decrease the space between joists but never increase the space. Live load psf dead load psf span calculator for wood joists and rafters available for the iphone.

Of course beefier sizes also increase your lumber bill. Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. Live load is weight of furniture wind snow and more. Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600.

Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. Span calculator for wood joists and rafters also available for the. Permissible clear span metres. For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are spaced 24 apart can have a maximum span of 10 feet 3 inches 10 3 if designing for a live load of 40 lbs ft 2.

A roof joist is always spaced no more than 16 inches apart from another roof joist. Wherever possible joists should span the shortest distance. 1 psf lb f ft 2 47 88 n m 2. The joists will normally be placed at 400mm centres but no more than 600mm centres.

Variations in ceiling construction nonparallel ceiling joist designs require additional support construction in the ceiling. Dead load weight of structure and fixed loads 15 lbs ft 2.