![]() To calculate the maximum spans of species not shown above, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website. The number of supports (beams or purlins) affects the allowable span length. Maximum roof slope is 5° for monoslope and 22.5° for pitched roof. Patio width is no less than 2.1m and length is no less than 3.5m. Patio height (hc) must always be less than roof height (h). To calculate maximum rafter spans using different design criteria (load, snow load, spacing, grade, etc.) for these common lumber species, see the International Residential Code (IRC). Average roof height between 3m and 6.5m (3m h 6.5m). The span values (displayed above) are from the American Softwood Lumber standard sizes. Rafters with ceiling not attached to rafters, ground snow load = 50 Psf, dead load = 20 Psf, deflection limit L/180 The following span table uses a moderate snow load of 50 Psf, but yours could be more or less. Consult your local building code authority to determine the snow load in your area. Note: Snow load factors can be specific to the regional location of a structure. Table 10. This example is a light roof in a low wind zone, so the Low and Medium multiplier of 1.3 can be used. Rafter Span Tables Rafters with ceiling not attached to rafters, live load = 20 Psf, dead load = 20 Psf, deflection limit L/180 Table 10.1 has span length multipliers for ‘Low and Medium’ and ‘High and Very High’ wind zones. The braces need to be supported by a bearing wall, shown in the diagram above.Įxample: In the rafter span table below, the highlighted cell (13-0) indicates that a 2" x 8" Douglas Fir rafter, with a grade of #2, spaced 24" apart, can have a maximum span of 13 feet - 0 inches (13-0) if designed for a live load of 20 Psf, and dead load of 20 Psf. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. Calculate FAQs How do you calculate rafter size Rafter size is determined by factors like span, roof pitch, snow load, and the type of wood used. Interior Framing Use iProSTUD in ClarkDietrich iTools to quickly lookup the interior framing system you need. ![]() Allowable limiting heights & span Charts Contact ClarkDietrich Technical Services at (888) 437-3244 for any questions on tables below. Non-Structural (ProSTUD) - Allowable Loads. ![]() When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports. Structural - Fastening Options & Allowable Loads. ![]()
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