How to Calculate Roof Pitch
Access a rafter., Position a level against the underside of the rafter., Find the 12 inch mark on the level., Measure the vertical distance from level to rafter., Find the slope.
Step-by-Step Guide
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Step 1: Access a rafter.
Measuring from the underside of the roof is usually the most accurate way to find the slope, since there is no roofing material to make an uneven surface.
Any of the following will give you a good measurement:
A rafter in the attic.
The overhang of a rafter at the end of the roof.
A barge rafter at the side of the gable. -
Step 2: Position a level against the underside of the rafter.
Place one end of a carpenter's level against the underside of the rafter.
Adjust the level until the bubble is centered between the two lines. , If your level does not have inch marking, measure it with a tape measure and draw on a 12 inch mark. 12 inches is the traditional measurement in the U.S.
If you don't have an imperial ruler, however, you can use any units.
Just use the same unit for all measurements, and measure a length at least this size (12 inches / 30 cm). , Extend your tape measure perpendicular to the level.
Measure the distance from the 12 inch mark to the underside of the same rafter, directly above it.
Make sure the level stays in position during this measurement. , The slope of your roof is the ratio of vertical distance (rise) to horizontal distance (run).
Just write down the measurements you found.
There's no need to simplify them.
For example, if you find 4 inches of height with the tape measure at the 12 inch mark on the level, your slope is 4:12 or "4 in
12." Most people looking for "pitch" are really interested in this measurement.
In technical terms, pitch has a different definition.
If you're not sure if you have the right measurement, skip down to find the pitch. -
Step 3: Find the 12 inch mark on the level.
-
Step 4: Measure the vertical distance from level to rafter.
-
Step 5: Find the slope.
Detailed Guide
Measuring from the underside of the roof is usually the most accurate way to find the slope, since there is no roofing material to make an uneven surface.
Any of the following will give you a good measurement:
A rafter in the attic.
The overhang of a rafter at the end of the roof.
A barge rafter at the side of the gable.
Place one end of a carpenter's level against the underside of the rafter.
Adjust the level until the bubble is centered between the two lines. , If your level does not have inch marking, measure it with a tape measure and draw on a 12 inch mark. 12 inches is the traditional measurement in the U.S.
If you don't have an imperial ruler, however, you can use any units.
Just use the same unit for all measurements, and measure a length at least this size (12 inches / 30 cm). , Extend your tape measure perpendicular to the level.
Measure the distance from the 12 inch mark to the underside of the same rafter, directly above it.
Make sure the level stays in position during this measurement. , The slope of your roof is the ratio of vertical distance (rise) to horizontal distance (run).
Just write down the measurements you found.
There's no need to simplify them.
For example, if you find 4 inches of height with the tape measure at the 12 inch mark on the level, your slope is 4:12 or "4 in
12." Most people looking for "pitch" are really interested in this measurement.
In technical terms, pitch has a different definition.
If you're not sure if you have the right measurement, skip down to find the pitch.
About the Author
Michelle Bell
A passionate writer with expertise in practical skills topics. Loves sharing practical knowledge.
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