How to Calculate the Pitch of a Roof
Roof pitch is a term often used in the construction and roofing industries. It refers to the angle of the roof in terms of inches of rise per inches of run. A "6-12" roof pitch means the roof rises 6 inches for every 12 horizontal inches. There are various ways of expressing roof pitch such as 6/12, 6 on 12, 6-12 and others. Calculating roof pitch is fairly simple, but you'll need to climb a ladder to do it, or access the roof rafters from the attic. Does this Spark an idea?
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Things You'll Need
- Ladder
- 3-foot flat board
- 2-foot level
- 2-foot ruler
- Scientific calculator
Instructions
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Use a ruler to measure and make a mark 12 inches from the end of the level. Use a ladder to access the roof.
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Lay a 2-foot board perpendicular to the slope of the roof so that it runs straight up and down. Set the level on the board and perpendicular to the slope with the end you measured from at the top. In an attic, you don't need the board. Hold the level against a rafter instead.
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Raise the end of the level up from the board or down from the rafter until the bubble is centered in the vial. Measure from the mark straight down to the board or straight up to the rafter. The distance measured is the rise, and the 12-inch mark on the level represents the run. If you measure 7 inches, the pitch is 7 inches of rise for 12 inches of run, or a 7-12 pitch.
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Calculate the roof angle if you need it using a scientific calculator with a tangent function. Divide the measured rise by 12. Press the "Inverse" key and press the "Tangent" key. The result displayed will be the angle of the roof.
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Tips & Warnings
The board lying on the roof is used to reduce errors caused by overlapping shingles, especially if there is more than one layer. Measuring a rafter in the attic or at a gable roof end is more accurate.
Use care when working with ladders. Place the ladder in a sturdy, level location, and get someone to hold the ladder as you climb it. Never lean far out to the left or right, as you could lose your balance and fall.
References
Resources
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