by John F Mann

Created on: January 04, 2010

There are several ways to determine the pitch or slope of a roof surface, including the use of satellite imaging technology. Most important however, is that you do not have to climb on the roof or even on a ladder to easily measure a roof slope.

For those who understand basic terminology, you can skip the first section. However, if you are not entirely sure of the lingo involved, take the time to read about the basics first.

PITCH OR SLOPE OF ROOF

Pitch of a roof is simply the slope of the roof surface with respect to a horizontal surface. Slope can also be visualized as slant, or tilt.

Click on the following link for a simple diagram that is essential for easy understanding.

http://structural101.com/RoofSlopeConversionTables.h tml

The following basic terms are used in discussion;

Rise = Change in vertical elevation between two points on a roof surface

Run = Change in horizontal distance between two points on a roof surface

For practical purposes, roof slope is most often reported as Rise divided by Run, also described as Rise "on" Run. When discussing roof slope, this fraction or ratio (yes, basic arithmetic!) is most often reported as the Rise per 12 inches of Run, such as 6 on 12.

Rise and Run must have the same units (inches or feet), although units are generally not reported since they "cancel out" in the ratio.

For single family houses with gable roof shape (A-frame), roof slopes typically range from 3 on 12 (minimum for shingles) to 12 on 12 (maximum). For row homes in older sections of towns and cities, the roof is often monoslope (one way) with very low slope, such as 1 on 12 or less.

Roof slope (pitch) can also be reported as the angle between horizontal line and sloping roof line (see diagram) measured in degrees. This slope angle can then be converted to a Rise-On-Run format using basic trigonometry or taken off a conversion chart (see end of article).

For a gable roof, the slope angle will generally be in the range of 14 degrees to 45 degrees.

WHERE TO TAKE MEASUREMENTS

Safety is of course essential when taking measurements of a roof. Falls from ladders are unfortunately high on the list of causes for serious injury and death.

Experienced contractors and competent, sure-footed homeowners can take measurements on top of a roof with relatively low (shallow) slope. However, the vast majority of homeowners should only take measurements inside the attic space (if feasible and safe), especially if roof slope is relatively high (steep) or the house is

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