So what does the 7/12 in the example to the left mean ?
The 7 means that the roof rises 7" for every 12" it runs. The example to left shows 2 different ways to determine or calculate roof pitch, also called roof slope.
In Example A, the measurements are taken from on top of the roof. Simply mark a level at 12", hold it perfectly level and measure from the roof surface to your 12" mark, this will give you the rise. Be careful with this method as a roof with many layers of shingles, or any type of roofing that is irregular can give you less than precise results.
In Example B, the measurements are taken from the bottom of the rafters, the procedure to calculate roof pitch is the same. This method tends to be more accurate because no layers of roofing are involved. To use this method there are 3 possible places to take your measurements. 1. The underside of a barge rafter on a gable end. 2. The underside of a rafter on an overhang at the bottom of the roof 3. The underside of a rafter in the attic.
You might see pitch referred to as "4/12", "4-12", "4 to 12", "4 and 12", "4 on 12".
Rule of Thumb:
If the roof is approximately 4 & 12 pitch with normal overhangs (1 1/2 - 2 feet), and if
the home is a single story, multiply the square footage of the home by 1 1/2 to get the
square footage of the roof. |