Things You'll Need
24-inch builder's level
You will need to calculate the slope or pitch of your home's roof when you are preparing to replace the roof on your house. There are different methods you can use to determine the slope of your roof, but none is easier than using a standard builder's level and a tape measure. With these two common tools, you can readily calculate the pitch of your home's roof. You will need to ensure that when you are measuring the slope of your roof, that you hold the level properly.
Set the extension ladder against the side of your house. Make sure that the ladder is not resting on the gutters of your home.
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Extend the ladder 3-feet beyond the edge of the roof, place your feet against the base of the extension ladder and stretch your arms straight out, toward the ladder. Your fingertips should barely reach the rung of the ladder nearest your eyelevel. Adjust the extension ladder as needed until your fingers touch the eyelevel rung of the extension ladder.
Stretch the tape measure along the 24-inch builder's level and place a 12-inch mark on the level with the soapstone.
Carefully climb the ladder and place one end of the 24-inch level on the surface of the roof.
Adjust the builder's level until the air bubble of the horizontal level vial rests perfectly in the center of the two marks on the vial and stretch the tape measure down to the surface of the roof, while keeping the tape measure aligned with the 12-inch mark you placed on the builder's level in step three.
Read the measurement on the tape measure at the location that the level and tape measure meet, this will be the slope or pitch of your roof. For example, if the builder's level crosses the tape at 6-inches, your roof is on a 6:12 pitch.