How to Calculate Roof Pitch Angle
To determine the pitch for a roof, you will need to take several measurements. The pitch refers to the angle, or slope, of a roof. The amount of the pitch is determined by the unit rise or your roof. On most home-building blueprints, you can find a small triangle called the "slope diagram." This diagram will show the unit run that is located at the base of the triangle and a unit rise that is located along the side of the diagram. Does this Spark an idea?
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Instructions
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1
Measure the total span. The total span is determined by measuring the outside of both exterior walls. To do this, hook the measuring tape to one wall and run the tape to the outside of the opposite exterior wall.
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2
Measure the total rise. The total rise is determined by measuring from the ridge of your roof to the top plate of your building. Convert this measurement to inches; an easy way to do this is to make a story pole.
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3
On the story pole, mark the top of your building top plate, and then place a mark higher up to determine the top of the roof ridge. The story pole can be a two-by-four board that is either marked or cut to the height of the building roof.
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4
Divide the total span measurement from step one by the number you determined in step two. Next, convert the divided total span to feet. Convert leftover inches to decimal feet; this measurement is the total run.
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5
Take the total rise from step two and divide this by your total run from step four; this measurement is the unit rise. The unit rise determines how many inches the roof rafter will rise vertically per foot of run.
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