Flat Roof Joist Spacing

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.

Flat roof joist spacing.

Dead load per square metre in kn m supported by joists. Permissible clear span metres. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. Centre to centre spacing of joists in mm joist size width depth mm 400 450 600 400 450 600 400 450 600.

A roof joist is always spaced no more than 16 inches apart from another roof joist. 2 are indicated below. Keep in mind that these are minimums for the spacing indicated you can select larger sizes to handle excessive loads or for appearance. The sizing and spacing will depend upon the loads imposed on them and the required span.

Live load psf dead load psf span calculator for wood joists and rafters available for the iphone. In other words you would space a roof joist 15 inches apart from another roof joist but never 17 inches apart. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. The same concept holds true for roof trusses.

1 psf lb f ft 2 47 88 n m 2. Live load is weight of furniture wind snow and more. Spacing in exterior exposure. If the roof is not completely square you can decrease the space between joists but never increase the space.

Span calculator for wood joists and rafters also available for the. Variations in ceiling construction nonparallel ceiling joist designs require additional support construction in the ceiling. Joist spacing of 24 inches is allowed for spans between 16 to 20 feet using 2 inch by 10 inch lumber of these three grades. So the space between rafters can be greater without reducing the maximum span.

Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. 1 ft 0 3048 m. The joists will normally be placed at 400mm centres but no more than 600mm centres. Dead load weight of structure and fixed loads 15 lbs ft 2.

Wherever possible joists should span the shortest distance. This is the distance between joist centres.