Roof Pitch Ratio Definition

The slope ratio represents a certain amount of vertical rise for every 12 inches of horizontal run.

Roof pitch ratio definition.

Sometimes pitch is also expressed in fraction form using a fraction. Roof pitch is used to describe the slope or angle of the roof. However most often a ratio of pitch also fraction is slang used for the more useful slope of rise over run of just one side half the span of a dual pitched roof. This measurement is best done on a bare roof because curled up roofing shingles will impair your measurement.

If asphalt shingles are to be installed on a low slope roof special steps are required to avoid short roof life and roof leaks. Often you express roof pitch as the ratio between the rise and the run in the form of x 12. The pitch of a roof is its vertical rise over its horizontal span. Pitch is thus the ratio of the rise in inches to a 12 inch run and is often expressed using a semicolon for example 6 12.

Notes to the table above. The picture below shows the pitch of a 7 12 roof slope meaning that for 12 of horizontal measurement roof run the vertical measurement roof rise is 7. This is the slope of geometry stairways and other construction disciplines or the trigonometric arctangent function of its decimal. You can assess this in two ways either as the roof pitch angles which the rafters make with the horizontal or the proportion between the run and the rise of the roof.

A roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a 4 in 12 slope. A roof with a 6 rise for every 12 run has a 6 per foot or 6 in 12 pitch. Some sources consider low slope to include 3 12 pitch roofs.