How to Figure Out the Run & Rise of Roofs

The slope of a roof, defined as the rise divided by the run, is the rate at which the height changes with respect to its length. The slope of a roof is important for many home-building and remodeling projects. In some areas, homes must be built with roofs of a minimum slope to prevent snow from adding too much weight to the roof. The calculation of slope is a basic mathematical operation taught in pre-algebra courses.

Measuring tape
Ladder

Instructions

- 1
  Measure the total vertical distance between a point at the lowest portion of the roof and a point exactly even with its apex.
- 2
  Measure the length of the roof from the apex straight out to a point directly above its lowest point, typically the ends of the eaves.
- 3
  Create a fraction with the vertical distance in the numerator and the horizontal distance in the denominator. For example, a roof with a vertical distance of 10 feet and a horizontal run of eight feet would yield a fraction of 10 / 8.
- 4
  Convert the units to inches. From the example above, 10 feet / 8 feet converts to 120 inches / 96 inches. Simplifying this fraction to a denominator of "12," representing the measure of inches in a foot, results in 15 inches / 12 inches or a rise and run of 15 / 12.

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