Roof Pitch Explained

Roof Online Staff

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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 roof 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 Three Ways to Express Roof Slope).

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 roof 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 roof 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