How to Measure a Roof's Pitch Through a Transparency
A roof's pitch, or slope, is a measure of the roof's steepness. Carpenters frequently measure the pitch of a roof in degrees, such that a complete circle has 360 degrees. They may also measure roof pitch in terms of the ratio of a roof's rise and run. For example, a roof with a 7/12 pitch rises 7 inches for every foot of its run. A roof pitch transparency is a transparency that contains a series of angles indicating common roof pitches. This devices provides a convenient method of estimating the pitch of a roof from the ground.
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Instructions
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Obtain a document that contains roofing angles such as the one available from Velux (see Resources).
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Print the roof pitch document onto transparency film using word processing software such as OpenOffice.
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Stand in front of one of the ends of your house so that you are exactly in the middle of that end of the house. Adjust your line of sight so that it is perpendicular to the end of the house. The measurement of your roof's pitch will be more accurate the farther you are from the house, so long as the house appears large enough to take the required measurements.
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Hold the roof pitch transparency in front of you. Adjust its position so that each of the two end points on the transparency is over one of the corners of the eave of the house.
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Locate the position of the roof's peak with respect to the vertices of the angles on the roof pitch transparency. The peak will be between two of the angles on the roof transparency. Estimate the pitch of the roof by interpolating the values corresponding to these two angles.
Assume for this example that the peak of your roof is exactly between the 15-degree angle and 20-degree angle on the roof pitch transparency. This means that the roof's pitch is exactly between 15 and 20 degrees, or 17.5 degrees.
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