| The slope of your roof is determined by the
vertical rise in inches for every horizontal twelve inch (12") length (called the
"run"). It is expressed with the rise mentioned first and the run mentioned
second. For instance, if your roof has a four inch (4") rise for every horizontal
foot, then it has a "4 in 12" slope (or pitch).

A fairly easy way to determine the slope is to take a
12" level and set one end on the roof surface and make it level. Then take a tape
measure or ruler and measure from the other end down to the roof surface. This will give
you the slope of the roof. The slope of the roof in the following picture would be
expressed as "4 in 12" or "4 on 12" and written as 4/12, 4:12, or
4":12".
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