Roof pitch is typically written as rise (vertical measurement) over run (horizontal measurement) with the run being 12 inches. So, a 45 degree roof would be a 12/12 pitch. To determine your roof pitch, use a framing square and a level or a level and a tape.
If you have access to a rake or barge board, use the framing square method. Hold the square so the horizontal 12" mark lines up with the top or bottom of the rake board or rafter and level it. Then read the measurement on the vertical scale. This will be your "rise".
For a hip roof or if you don't have access to a rake or possess a framing square, set one end of a level on the roof and hold it level. Using a measuring tape, rule, or yard stick, measure vertically from the bottom of the level to the roof. Divide this number by the length of the of the level (by 4 if using a 4 foot level for instance) and this will be your "rise".
You can also use your chimney or wall to determine the pitch if you only have a measuring device. Measure horizontally along a brick joint or other horizontal line from where it intersects the roof to a point 12" from the roof. Measure vertically from this point to the roof. This will be your "rise".
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