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. The standard spacing for metal roofs is four to six feet. There may be a different gap between members depending on the code requirements. 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). Credit: Roof joist and rafter spacing is typically 12-16, 19-19.2, and 24 on center, but rafters are typically spaced 16 or 24 on center. In high-wind areas, uplift can tear a roof off of a house if its not. The span values (displayed above) are from the American Softwood Lumber standard sizes. They must be spaced no more than 4 feet (1219 mm) apart. Rafters with ceiling not attached to rafters, ground snow load = 50 Psf, dead load = 20 Psf, deflection limit L/180 Some homeowners try to cut down on roof replacement costs by using as few furring strips as possibleor skipping out altogether despite contractor recommendations. Standing seam metal roofing: space your strips up to 18 inches apart. The following span table uses a moderate snow load of 50 Psf, but yours could be more or less. Here are some spacing guidelines based on type: Corrugated metal roofing: space your strips up to 24 inches apart. 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 When possible, always attempt to divide the roof areas into equal sections, with. 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. Do not exceed 25 feet vertically between staggered patterns of snow guards. The type of roofing material to be applied over the sheathing also plays a. When 16-inch OC rafter spacing is used, the minimum recommended thickness is 3/8 inch. The larger the spacing, the greater the thickness of sheathing that should be used. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. The distance between rafters (spacing) is one of the most important. When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports. Typical construction for residential roofing consists of rafters or trusses spaced 16 or 24 on center and at a pitch, or roof slope, of 3/12 up to 12/12.
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