![]() One more thing: if you’re using this table, you should consider getting yourself a construction calculator. It will tell you the slope of your roof in degrees, rise/run, or percentage, and automatically convert from one to the other.Ĥ. It may be way too expensive for what you need, but this is what professionals use. If you want to know the slope of anything to an amazing degree of accuracy and you like cool new tools, you should check out this digital level. If you’re not sure what the pitch of your roof is and you want to figure that out, we recommend this slope finder on Amazon. (You can use this free online scientific calculator.) For example, if the roof pitch is 45°, then sec(45) = 1.414213. If you know the roof pitch in degrees, find the secant of the slope using a scientific calculator. The following table provides the roof pitch factor for roofs of various slopes. For a more detailed explanation of the roof pitch factor, see “ How to Find the Area of a Sloped Roof“.Ģ. To find the location of the heel cut, the factor is multiplied by the “ effective run” of the rafter. The effective run is the horizontal distance covered by the rafter from the near side of the ridge board, where the head cut will be, to the outside of the wall plate, where the heel cut will be.Īlways measure for every rafter, even being off ⅛-inch can make a big difference if the error gets multiplied as you go along. That will give you the proper rafter length. Multiply the roof pitch factor by the run of the rafter (the horizontal distance covered by the rafter). Once you know the actual horizontal distance it will cover, use the formula above. To find the length of a common rafter, determine its span from the bottom of the end of the rafter tail to the top of the ridge cut at the ridge board. The roof pitch factor is used to calculate the length of common rafters. ![]() ( There’s a good calculator online here.) Roof Pitch Factor & Common Rafters ![]() So you divide the rise by the run (the run is always 12 and the rise depends on your particular roof). A roof pitch of 4-in-12 (4:12) has a rise of 4 and a run of 12. Remember that the slope of the roof provides the rise and the run to be plugged into the equation. Once you know your roof slope expressed as “X-in-12″ (rise-in-run), the roof pitch factor is determined by finding the square root of ((rise/run)² + 1). You will need to know the slope of your roof in the standard pitch format “X-in-12″ for the rest of this page to make sense.įor help converting from degrees or percentage to traditional pitch, see our pages Roof Slope Equivalents or Roof Pitch to Degrees Use the Traditional Pitch Format to Find the Factor You multiply the roof pitch factor by the run (length of the horizontal distance covered) of a common rafter to find its actual length. You multiply the roof pitch factor by the area, or footprint, covered by a sloped roof to find the actual surface area of the roof. A roof pitch factor, also called a roof pitch multiplier, is a number that you use to find the actual surface area of a pitched roof or the length of a common rafter.
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