Roof Pitch Explained • Roof Pitch Chart

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What is Roof Pitch?

Roof pitch is a mathematical expression of how steep your roof is. When using pitch, the slope of the roof is given as a ratio of the vertical rise to the horizontal run (rise/run).

Traditionally, this expression of pitch takes the form “X:12″ or “X-in-12″, where X is the number of units (inches) of vertical rise of the roof and 12 inches is the run.

12 is always used for the run because there are 12 inches in a foot, and you are stating how many inches the roof rises over a one foot span.

Places that don’t use inches typically don’t use standard roof pitch, either. Instead, they express roof slope in degrees.

The steepness of a roof may be expressed in degrees or as a percentage (see Ways to Express Roof Slope: Pitch, Degrees, and Percentage).

Low-Slope vs. Steep-Slope Roofs

A low-slope roof is commonly called a “flat roof”, although building codes forbid perfectly flat roofs and require all flat roofs to have some slope. This requirement is intended to ensure that water will drain off the roof. Perfectly flat roofs would be at a much higher risk of overloading and collapsing due to standing water.

A low-slope roof will typically have a pitch between ¼-in-12 and 2½-in-12. The technical definition of a low-slope roof is any roof having a slope of less than 3-in-12 (approximately 14 degrees above horizontal).

Any roof with a slope of 3-in-12 or above is a steep-slope roof.

Low-slope roofs typically have membrane-style roof coverings and steep-slope roofs typically have shingles or tiles. Because shingles and tiles can also sometimes be installed on roofs that have a pitch under 3-in-12 (as low as 2-in-12 if special underlayment requirements are met) there is often confusion about where the cut-off point is between low-slope and steep slope roofs. It’s 3-in-12. Any use of asphalt shingles, for example, on a roof with a pitch below 3-in-12 is considered a “low-slope application” of the shingles.

Generally, although there are exceptions (such as with asphalt shingles), low-slope roofs will use a different set of materials, have different installation techniques, and have far different maintenance requirements than steep-slope roofs.

Why Roof Pitch is Important

  1. The pitch of a roof determines what roofing materials can be used on the roof (see Minimum Roof Pitch for Every Roofing Material).
  2. The pitch of a roof is an important factor in figuring out how much roofing material will be needed when installing a new roof, because it allows you to accurately calculate the surface area of the roof (see How to Find the Area of a Roof).
  3. The pitch of a roof is important when making certain roof drainage calculations (see Roof Drainage).
  4. The pitch of a roof determines the roof slope factor, also called the roof slope multiplier, which is used to calculate proper rafter length as well as roof area.
  5. The pitch of a roof determines the hip and valley factor, which is used to calculate the proper length of hip and valley rafters.

More Roof Pitch Pages

See our Roof Pitch Multiplier Chart for a much longer list of roof slope factors, including slope factors for roof pitches by the half-inch. We also explain the math behind the multiplier.

See our Hip and Valley Factor Chart for a much longer list of hip and valley factors, including hip and valley factors for pitches by the half-inch. We also explain the math behind the factor.

Roof Pitch to Degrees  Degrees to Roof Pitch has conversion charts that convert slopes from 1 to 72 degrees into standard pitch and roof pitches from ⅛-in-12 to 36½-in-12 into degrees.

Minimum Required Roof Pitch for Every Roofing Material explains why you shouldn’t use a roofing material on a slope that is lower than recommended, and has a chart showing the minimum slopes required by the building code.

Roof Pitch Chart

Roof Pitch Chart
Pitch of Roof Roof Slope in Degrees Roof Slope Factor Hip and Valley Factor
¼:12 1.193° 1.0002 1.4144
½:12 2.386° 1.001 1.4148
1:12 4.76° 1.003 1.4167
2:12 9.46° 1.014 1.4240
3:12 14.04° 1.031 1.4362
4:12 18.43° 1.054 1.4529
5:12 22.62° 1.083 1.4743
6:12 26.57° 1.118 1.5
7:12 30.26° 1.158 1.5298
8:12 33.69° 1.202 1.5635
9:12 36.87° 1.250 1.6008
10:12 39.81° 1.302 1.6415
11:12 42.51° 1.357 1.6853
12:12 45° 1.414 1.7321
13:12 47.29° 1.474 1.7815
14:12 49.4° 1.537 1.8333
15:12 51.34° 1.601 1.8874
16:12 53.13° 1.667 1.9437
17:12 54.78° 1.734 2.0017
18:12 56.31° 1.803 2.0616