AWC’s Appendix A lists a variety of live and dead load combinations for floors, ceilings and rafters. 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. Simply reference Span Tables for Joists and Rafters published by the American Wood Council (AWC). 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). Span Tables for Rafters (to BS 5268-7.5) Imposed loads of 0.75 kN/m² snow load are applicable to most areas where the altitude does not exceed 100 metres (refer to BS 6399-3) Imposed loads of 1 kN/m² snow load are applicable to most areas where the altitude exceeds 100 metres but does not exceed 200 metres, but excluding parts of Scotland. ![]() 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. Pergola Rafter Spans for 600 mm and 900 mm Spacing and. 3) For design parameters, refer to figure 6.22, AS1684.2 and 3. Member span is not suitable for rafter spacing greater than 600mm. Note: Snow load factors can be specific to the regional location of a structure. Notes: 1) Refer to general notes for information that is relevant for all span tables. ![]() Rafter Span Tables Rafters with ceiling not attached to rafters, live load = 20 Psf, dead load = 20 Psf, deflection limit L/180 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. Rafter span tables - Use these tables into ascertain lengths, sizes and spacing a sills based on an variety of factors such as, species, load, grade, and spacing. ![]() Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports. ICC Digital Codes is the largest provider of model codes, custom codes and standards used worldwide to construct safe, sustainable, affordable and resilient structures.
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