How to Figure the Pitch of a Roof
The pitch of a roof is a measure of its steepness. Carpenters typically express roof pitch as the number of inches that the roof rises for each foot of run. A roof with a 4/12 pitch therefore rises 4 inches for each foot of its run. Roof pitch is an important factor in a roof's construction, as it determines the ease with which snow slides off the roof. One method of measuring roof pitch involves accessing the attic rather than climbing onto the roof. Does this Spark an idea?
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Instructions
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1
Locate a rafter that is parallel with the roof line. You can typically find such a rafter under the eave of the roof or in the attic.
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Attach the string of a plumb bob to the underside of the rafter. Steady the plumb bob's weight so that it hangs freely without moving.
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Hold the carpenter's level in the horizontal position so that the carpenter's level is on the side of the plumb bob where the rafter is lower. Place the upper corner of the carpenter's level that is furthermost from the plumb bob so that the 1 foot mark on the carpenter's level aligns with the plumb bob.
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Tilt the free end of the carpenter's level as needed to keep its bubble centered within its container, indicating it is exactly horizontal.
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Mark the plumb bob's string at the point where the top of the carpenter's level crosses the string of the plumb bob.
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Measure the distance from the mark on the plumb bob's string to the underside of the rafter with a tape measure. Assume for this example that this distance is 5 inches. The pitch of the roof is therefore 5/12.
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