3/16/2024 0 Comments Roof rafter span table 802.5.1![]() 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). 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 Figure 802.5.1 Braced Rafter Construction. Table R802.5.1(9) Rafter/Ceiling Joist Heel Joint Connections. The following span table uses a moderate snow load of 50 Psf, but yours could be more or less. Table R802.5.1(8) Rafter Spans for 70 PSF Ground Snow Load. Consult your local building code authority to determine the snow load in your area. Each time we fail someone for non-compliance we always hear how they just. Note: Snow load factors can be specific to the regional location of a structure. The moral of the story is that the requirement for nailing this overlap in accordance with 802.5.1 (9) per the 2009 IRC is often overlooked by both inspectors and framers. Rafter Span Tables - Use these tables to determine lengths, sizes, and spacing of rafters based on several factors such as species, load, grade, and spacing. IRCTables R802.5.1(1) - (8) Knee walls or roof purlins must be the same size as the roof rafters, with the rafters supported by the narrow edge of the purlin and not the flat side. Rafter Span Tables Rafters with ceiling not attached to rafters, live load = 20 Psf, dead load = 20 Psf, deflection limit L/180 IRC Tables R802.4(1) and (2) Check spans of roof rafters. 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. Chapter 8 also provides requirements for the application of ceiling finishes, the proper ventilation of concealed spaces in roofs (for example, enclosed attics and rafter spaces), unvented attic. When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports. Allowable span tables are provided to simplify the selection of rafter and ceiling joist size for wood roof framing and cold-formed steel framing. With consideration for R802.3 and Table R802.5.1(3), (2006 IRC), based on a common rafter length of a little under 20, it is plausable that 2x10 common rafters attached to 2x12 hip rafter can be used prescriptively where common rafters are 12' O.C.
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