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. LVL USER’S GUIDE 3 WEST FRASER TIMBER Product Line 4 Storage, Handling & Installation 4 3100Fb2. 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). 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. 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 ARE CONTINUOUS OVER THE BEAM, MULTIPLY TRIBUTARY WIDTH BY 1,25 AND ALWAYS. 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. 1- TABLE ASSUME UNIFORM LOADS AND SINGLE FLOOR JOIST SPANS. Table values relate to Allowable Maximum Span in. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. Concentrated Loads: No allowance has been made in the tables. ![]() Note: The 140 × 70 mm rafter size permitted to span 2.9 m could also have been used (since 2.9 × 1.1 multipler 3.19 m), but this is not a stock size so was not chosen. This indicates a 190 × 45 mm rafter size. ![]() When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports. Rafters 12 Ceiling Joists 15 Hanging Beams member16 Underpurlins 17 Strutting Beams 18 Roof Beams 20 Verandah Beams 22 Garage Roof. Read the rafter size in the left column of Table 10.1 for the 3.3 m span chosen. 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.
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