The Ridge Height can be calculated using the same formula as the Ledger Height on a Shed Roof. Once you have verified the first rafter, you can use it as a template to lay out the remaining rafters.Ĭalculating rafter sizes and spacing is the same for a gable roof as it is for a shed roof. Roof framing is easy, right? Please verify all of the measurements before you start cutting rafters. Ledger Height (from the top of the slab) = Wall Height + Rafter Rise(M) + Y Wall Height: 96 inches (assuming an 8-foot wall).Now that the 'Y' height is known, you have the data you need in order to calculate the Ledger Height. Using the Rafter Span Tables on, you can see that 2圆 rafters (Southern Pine #2 Grade), spaced 16 inches apart, will span 8-5 (8 feet - 5 inches). Rafter Run: 8 feet (horizontal distance between my Ledger and outer wall).Rafter Material: Southern Pine #2 Grade (because it is the most widely used framing lumber in my region).Design Load: 70 PSF ( snow load of 50 PSF and a dead load of 20 PSF).Rafter Run: This is the horizontal distance between supports.įor this example, let's say you have the following design criteria:.Rafter Material: Select an available species of framing lumber in your area.Design Load: - This is the Dead Load (weight of the framing) + Live Load (wind, snow, etc.).To determine the size of the rafters, using span tables, you need to know three things: When you are preparing to build a shed roof, you must first engineer the rafters - that is, know the species of wood you will use for the rafters, the nominal size of the rafters (2圆, 2x8, etc.), and the spacing of the rafters.
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