Flat Garage Roof Timber Sizes

Completely flat roofs typically present weather proofing problems so the rafters or joists of some flat roofs are laid at a slight angle for drainage.

Flat garage roof timber sizes. Common joists sizes are 200 x 50mm 175 x 50mm and 150 x 50mm. Wherever possible joists should span the shortest distance. The joists will normally be placed at 400mm centres but no more than 600mm centres. 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.

The sizing and spacing will depend upon the loads imposed on them and the required span. There are several variables to consider when determining the proper rafter 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. This sizing guide for roof rafters will help determine what you need for your small project.

Supporting imposed load for access and repair only. The size of rafters for a flat roof depends on the horizontal span of the building the type and grade of timber used and the load on the roof. This is the distance between joist centres.