Another option are 2 X 8 rafters spaced 24 inches o.c. The table states that 2 X 6 rafters spaced 16 inches on center (o.c) can span a maximum distance of 13 feet 5 inches. Looking through the center of the table, we can find a couple of options. Let's use this example and find a size of rafter that will work. So if your house is 26 feet wide and the roof ridge beam is centered on the house, you will need a rafter that can span 13 feet. The maximum spans in the table above are for the horizontal distance the rafter can span (NOT the diagonal distance or actual length of the rafter). This table is simply a sample and may not be valid for your region. Sample Maximum Spans (feet-inches) Douglas Fir or Larch, No.1 or No.2 with 31.3 psf of Snow Loading Let's look at the sample table below which shows maximum rafter spans for a snow load of 31.3 pounds per square foot (psf).įraming Table for Maximum Roof Rafter Spans If you live in a region that gets winter snowfall, contact your municipal building department to find out what maximum snow loads you need to design for.ĭepending on your region, you may need to design for a maximum snow load of anything between zero to 65 pounds per square foot (or roughly 0-3 kPa). All roof framing tables are organized by maximum snow load. In most regions, the first thing to consider before sizing the wood framing members for a roof is the maximum snow load that the roof will have to bear. Initially, we will discuss the framing of gable roofs so that we can learn the basics of how to size a roof rafter, beam or joist. Each rafter is in turn fastened to the top of the exterior structural walls.Īs we discussed in Exterior House Designs there are many different house roof types. Along the top center of the house there is a beam to which are attached the rafters. The image below shows a cross-section of our simple 12' X 13' house from the joist span tables section of this tutorial. Let's consider a basic gable wood roof framing design. Continuing on from Part 3: Floor Beam Span Tables of Residential Structural Design, we will now look at roof rafter and beam design.
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