Flat Roof Rafter Spacing

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.

Flat roof rafter spacing.

Dead load weight of structure and fixed loads 15 lbs ft 2. 1 psf lb f ft 2 47 88 n m 2. The rafters in a flat roof serve as ceiling joists for the space below. Live load is weight of furniture wind snow and more.

So the space between rafters can be greater without reducing the maximum span. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. Maximum rafter spans for a patio roof in areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot.

2 are indicated below. 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. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. The same concept holds true for roof trusses.

They are nailed securely to exterior wall plates and to each other. 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.