Flat Roof Joist Spacing

The joists will normally be placed at 400mm centres but no more than 600mm centres.

Flat roof joist spacing.

The sizing and spacing will depend upon the loads imposed on them and the required span. 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. So the space between rafters can be greater without reducing the maximum span. A roof joist is always spaced no more than 16 inches apart from another roof joist.

Span calculator for wood joists and rafters also available for the. Keep in mind that these are minimums for the spacing indicated you can select larger sizes to handle excessive loads or for appearance. Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. 2 are indicated below.

Of course beefier sizes also increase your lumber bill. 1 psf lb f ft 2 47 88 n m 2. In other words you would space a roof joist 15 inches apart from another roof joist but never 17 inches apart. 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.

Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. This is the distance between joist centres. Live load psf dead load psf span calculator for wood joists and rafters available for the iphone. Usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size automatically calculate sizes suitable for supporting the loads below.

Dead load weight of structure and fixed loads 15 lbs ft 2. Dead load per square metre in kn m supported by joists. Permissible clear span metres. Wherever possible joists should span the shortest distance.

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. Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. Live load is weight of furniture wind snow and more. The same concept holds true for roof trusses.

1 ft 0 3048 m. Variations in ceiling construction nonparallel ceiling joist designs require additional support construction in the ceiling.