![]() 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. If you know load, quality of wood, rafter frequency, and span, for example, you can calculate the cross - sectional dimensions of the. Note: The design values shown in the table are for normal load duration and dry service conditions and are applicable to lumber surfaced either unseasoned (S-GRN) or dry (S-DRY or KD). Choose one or more species/species grouping(s). 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). Max Span Calculator Carson Swope T11:35:00-07:00. The span values (displayed above) are from the American Softwood Lumber standard sizes. (2) Spans for floor joists that are not selected from Tables A-1 and A-2 and that are required. Compared to the dead load the snow load is not following the slope of the rafter. (1) Except as required in Sentence (2) and Article 9.23.13.10., the spans for wood joists and rafters shall conform to the spans shown in Tables A-1 to A-7 for the uniform live loads shown in the Tables. This load is now applied vertically to the pitched roof. Rafters with ceiling not attached to rafters, ground snow load = 50 Psf, dead load = 20 Psf, deflection limit L/180 The snow load for this pitched roof located in Copenhagen, Denmark is calculated as. The following span table uses a moderate snow load of 50 Psf, but yours could be more or less. Span Tables for Rafters (to BS 5268-7.5) Imposed loads of 0. 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. 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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