![]() ![]() ![]() For other grades and species and for other loading conditions, refer to the AWC STJR. Rafter spans shall be measured along the horizontal projection of the rafter. It's recommended to use a joist span calculator or to refer to a joist sizing and span table. Rafters shall be sized based on the rafter spans in Tables R802.4.1(1) through R802.4.1(8). If the deck will have a diagonal layout, then reduce the spacing to account for the additional distance the boards must cross between joists.Ĭalculating the deck joist span is significantly more difficult and requires the use of several different formulas. Typically, going with 12-inch or 16-inch joist spacing is a safe bet for the project, but if you want to ensure the spacing is adequate for the project, use the following formula:ĭeck Length ÷ (Number of Joists - 1) = Joist Spacingįor example, a deck that measures 20 feet or 240 inches in length with 16 joists should have 16-inch joist spacing. Example: In who rafter span table slide, the highlighted per (13-0) indicates that a 2' x 8' Douglas Fir rafter, with a grade of 2, spaced 24' apart, ability have a maximum span on 13 feet - 0 inches (13-0) wenn designed for a live lade of 20 Psf, and dead load of 20 Psf. Joists are generally spaced either 12 inches or 16 inches on center, though some builds may opt for eight inches or 24 inches on center. Once you know the material, joist size, and you have a plan with the intended size and shape of the deck, you can calculate the desired deck joist span and spacing. Redwood, Western Cedars, Ponderosa Pine, Red Pine Maximum Joist Span with 16 Inch Joist Spacingĭouglas Fir-Larch, Hem-Fir, Spruce-Pine-Fir Maximum Joist Span with 12 Inch Joist Spacing The Spruce Home Improvement Review Board.Joists supporting additional loads should be calculated by a competent person. These span tables make no additional allowance for partitions or any other loads additional loads. BS 5268-7.1 was published before BS 6399-1 was amended to include the more onerous 1.4 kN imposed concentrated load, so the approach adopted for these span tables uses the recommendations given in BS 6399-1, however, both approaches do result in similar joist sizes being calculated. Visit the roof framing page for see information on cutting roof girders, and visit the rail pitch calculator for definition rafters widths based on rise and run. Other span tables are based on the guidance given in BS 5268-7.1 which is a uniformly distributed load of 1.5kN/m² for spans greater than 2400 mm and 3.6 kN load per metre width of floor for spans less than 2400 mm to ensure that very small joist sizes do not result from the calculations for smaller spans. Balk Span Tables - Use these tables till determine lengths, sizes, and spacing of rafters based off multi factors that as sort, load, grade, and spacing. The floor joist span tables are based on the loadings given in the amended version of BS 6399-1 which is an imposed load of either a uniformly distributed load of 1.5 kN/m² or a concentrated load of 1.4 kN. Joists are to have minimum end bearing of 40mm. Wane as allowed in BS 4978:2007+A2:2017 is permitted in all sections included in these span tables. Proprietary strutting is to be used in accordance with manufacturers recommendations. ![]() Solid timber strutting to be at least 38mm thick and be a minimum of three quarters of the joist depth.
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