How to Determine a Roof Slope


The slope of a roof is also called the pitch. The roof slope is calculated by determining how many inches the roof rises for every foot of the roof's length. The length of the roof is also called the run. The run is the measurement from the peak of the roof to the edge. You don't have to climb to the top of your roof to determine the slope. You can either determine the slope by measuring on the edge of the roof or from inside the attic.

Things You'll Need

  • Ladder
  • Safety harness (optional)
  • Tape measure
  • 12-inch level
  • Set a ladder against the roof in a secure manner. Protect the gutters from scrapes by making sure your ladder extends above the roof line. If the roof is high, use a safety harness for protection.

  • Set a 12-inch level on the roof. Run the level perpendicular to the edge of the roof. If your level is longer than 12 inches, let the excess hang over the roof edge. Allow one end of the level to rest on the roof. Center the bubble in the level. The end closest to the roof edge will be elevated.

  • Measure the distance from the bottom of the level to the roof. If there is more than one layer of shingles or roofing material on the roof, account for the space. For accuracy, your measurement must be to the top of the sheeting. This measurement is called the rise.

  • Calculate the slope of your roof by entering the numbers in the order of rise and then run. For instance, if the rise is 4 inches, your roof slope is 4 inches by 12 inches, or 4:12. If the rise is 5 inches, the slope is 5:12.

Tips & Warnings

  • You can also find the roof slope by accessing the attic and setting the level against the flat of the roof and dropping one end until the bubble is centered. Measure from the roof to the top of the level.

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  • Photo Credit Jupiterimages/ Images Brand X Pictures/Brand X Pictures/Getty Images Hemera Technologies/ Images
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