Flat Roof Rafter Span

The rafters in a flat roof serve as ceiling joists for the space below.

Flat roof rafter span. Rafter span tables use these two tables for roof rafters with a slope of 3 in 12 or less. 2 are indicated below. 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. The tables below give maximum spans for rafters and beams.

This is set by the roof use you selected in the previous screen and cannot be modified. Dead load weight of structure and fixed loads 15 lbs ft 2. Wood beam calculator american wood council website rafter and joist span faq. 2 4 rafters can span up to 7.

Input the rafter span on the flat eave overhang and pitch of the roof. Click the button to calculate the stock size needed for this job. Use these two tables for roof rafters with a slope greater than 3 in 12. For light load roofs 24 o c.

The above spans are based on american softwood lumber standard sizes. Input the rafter span on the flat eave overhang and pitch of the roof. This calculator is to be used as an estimating tool only. Live load is weight of furniture wind snow and more.

Click the button to calculate the stock size needed for this job. Spacing your 2 4 shed rafters at 24 on center limits the width of your roof. Span calculator for wood joists and rafters also available for the android os. For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements.

Live load 20 lbs ft 2 956 n m 2. Also available for the android os. The lengths and sizes of joists vary depending on the species and quality of the lumber used. Most roof framing is 24 on center and you can still build sheds up to 14 with 2 4 rafters at 24 on center.

For heavy loads 2x4s can span up to 5. They are nailed securely to exterior wall plates and to each other. Live load overhang kpa. For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine.

The imposed uniformly distributed live load in the main span. 1 in 25 4 mm. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. 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.

The 1 grade. Loads are calculated in accordance with table 3 1 of as nzs 1170 1 2002. Rafter stock size calculator.