3/15/2024 0 Comments Rafter span tables![]() 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. 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). Otherwise, the roof load and external pressures can exert too much weight on the framing. For instance, space the rafters 12 inches apart on-center for a 16-foot span. However, the actual spacing depends on various factors, notably the rafter span. The span values (displayed above) are from the American Softwood Lumber standard sizes. The ideal spacing for 2×6 rafters is 16 or 24 inches on-center. 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. These span tables are the equivalent of other industry-standard span tables and are calculated to the same standards. These spans were calculated using our flat roof joist calculation engine. This span table is to the format and methodology given in BS 5268-7.2. Consult your local building code authority to determine the snow load in your area. Click on a span to generate a full calculation (you can adjust the exact span). Note: Snow load factors can be specific to the regional location of a structure. 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. 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.
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