Flat Roof Joist Spacing

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

Flat roof joist spacing.

Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. Spacing in exterior exposure. Of course beefier sizes also increase your lumber bill. If the roof is not completely square you can decrease the space between joists but never increase the space.

Not more than 0 5 more than 0 5 but not more than 0 75 more than 0 75 but not more than 1. The sizing and spacing will depend upon the loads imposed on them and the required span. 2 are indicated below. Permissible clear span metres.

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. Span calculator for wood joists and rafters also available for the. 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 per square metre in kn m supported by joists.

Wherever possible joists should span the shortest distance. Keep in mind that these are minimums for the spacing indicated you can select larger sizes to handle excessive loads or for appearance. A roof joist is always spaced no more than 16 inches apart from another roof joist. 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. 1 psf lb f ft 2 47 88 n m 2. 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. This is the distance between joist centres.

In other words you would space a roof joist 15 inches apart from another roof joist but never 17 inches apart. The same concept holds true for roof trusses. Variations in ceiling construction nonparallel ceiling joist designs require additional support construction in the ceiling. Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm.

Live load psf dead load psf span calculator for wood joists and rafters available for the iphone. Dead load weight of structure and fixed loads 15 lbs ft 2.