Term Description
Low-slope roofs

A category of roofs that generally includes weatherproof membrane types of roof systems installed on slopes at or less than 3:12.

Roof slope

The angle a roof surface makes with the horizontal, expressed as a ratio of the units of vertical rise to the units of horizontal length (sometimes referred to as "run"). For English units of measurement, when dimensions are given in inches, slope may be expressed as a ratio of rise to run, such as 4:12, or as an angle in degrees.


The angle of incline, usually expressed as a ratio of rise to run, or as an angle. See "roof slope."

Steep-slope roofs

A category of roofing that generally includes water-shedding types of roof coverings installed on slopes exceeding 3:12.