How to Figure Slope in a Roof

Many roofs have a slope. The slope of a roof is determined by the rise and run of the roof, similar to the slope of a triangle. The run of the roof is how long it is from the tip to the base if you drew a straight line. The run is the height from the base of the roof to the tip of the run, making an imaginary triangle. Roof slope is calculated for every 12 inches of run.

2 rulers
Ladder
Assistant

Instructions

- 1
  Lean a ladder against your roof and have someone hold the base while you climb the ladder.
- 2
  Set a ruler against the roof and hold it straight out horizontally so it measures at least 12 inches of the roof.
- 3
  Set a second ruler on the roof and hold it vertically so it meets the first ruler.
- 4
  Note the number of inches indicated on the second ruler. The slope of the roof will be a fraction that looks like this: rise/run. For example, if the rise is 5 inches, the slope would be 5/12; 12 inches is always the roof's run.

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