![]() 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). Rafters the ceiling not attach go balks, ground snow load 50 psf, dead load 20 psf, deformation limit L/180. The following span table uses a moderate snow load of 50 psf, but yours could be more or less. The span values (displayed above) are from the American Softwood Lumber standard sizes. Consult your local building code authority to determine the snow load in your area. Rafters with ceiling not attached to rafters, ground snow load = 50 Psf, dead load = 20 Psf, deflection limit L/180 Standard AS1720.3 Dynamics for 1.0kN Static Load. The following span table uses a moderate snow load of 50 Psf, but yours could be more or less. Floor Live Load 1.5kPa/1.8kN OR 2.0kPa/1.8kN. 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. 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. Plain ceilings are sized at 10 lb loads, while the ceilings with storage are sized for 20 lb loads. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. Find the maximum spans for ceiling joists according to the 2018 International Residential Code using the most common types of lumber with these simplified span tables. When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports.
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