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Roofr By Roofr • November 10, 2017

Why Slope Matters in Roofing

Roof Slope and Project Estimates

Roof slope is one of the biggest factors that professionals consider when calculating a price for a roofing job. A steep roof may present a number of challenges. Generally, the steepness of a roof relates to how much risk is involved with the project, especially if it is on a tall building. Working on a roof with a steeper angle may also require bringing in more equipment and taking longer to deal with issues. All of this is factored into your roofing estimate.

The Ratios

The pitch of a roof is commonly expressed as a ratio or fraction. The rise is stated in inches of height per 12 inches of length. For example, a 4/12 grade on a roof means the surface rises 4 inches for every 12 inches of length.

This can lead to some misleading math. While 12/12 as a fraction sounds tame, it actually means that a roof rises very aggressively for every foot of distance. Conversely, a 1/12 grade is actually rather flat.

Conversion table:

Roof Pitch Angle Roof Pitch Multiplier
1/12 4.76° 1.0035
2/12 9.46° 1.0138
3/12 14.04° 1.0308
4/12 18.43° 1.0541
5/12 22.62° 1.0833
6/12 26.57° 1.1180
7/12 30.26° 1.1577
8/12 33.69° 1.2019
9/12 36.37° 1.2500
10/12 39.81° 1.3017
11/12 42.51° 1.3566
12/12 45.00° 1.4142


Calculating Pitch

One of the easiest and safest ways to calculate roof pitch is from inside your attic using a level, tape measure, and pencil. First, measure 12 inches on your level and make a mark. Then, hold the level flat against the bottom of a rafter while making sure the level bubble is centered between the two lines.

The final step is to measure vertically from the 12-inch mark on the level to the underside of the rafter above it. The distance from the level to the rafter shows you how much your roof rises for every 12 inches of length. This is a good rough figure that you’ll be able to pass along to a contractor.

At Roofr, we help customers connect with contractors quickly. Knowing the angle of a roof will enable you to provide better information as you receive multiple estimates through our system. Contact us today to start the Roofr process.

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