A roof pitch angle is determined by calculating the rise versus the run or elevation slope of the roof. This measurement can be taken from inside your attic (the safest way) or you can climb on the roof to make the determination. Either method will require the use of a tape measure and pencil in order to make the calculation.
You are going to have to take several measurements in order to obtain the roof pitch angle. The pitch is another term used to describe the angle or slope of your roof. The amount of slope is created by the amount of units the roof goes up, or rises versus the amount of units it runs or moves in to the next rise. The units are the measurement that your builder uses and can be found on the roof diagram in the blueprint.
It is highly recommended to take the measurements in the attic as oppose to climbing on the roof. Although either method will produce the same measurement, it is safer to work inside as oppose to from the roof. You may not need the assistance of another person to accomplish the measurements working inside.
Tools and Materials Needed:
Step 1: Measure the Roof Span
You will need to take a measurement of the roof span. This is done by running the tape measure from one end of the roof to another. Either attach the tape measure to one wall or ask for assistance and run it to the other end of the roof.
Step 2: Determine the Rise
After measuring the roof span, you will need to determine the rise of the roof. From the inside measure the rise by taking a level against the roof rafter and run the tape measure against. Bend the tape the measure and point it toward the nearest wall. This will give you a measurement of the number of inches the roof goes up per 12 inches (making your units inches).
On the outside, rest the level on the roof and run the tape measure against it, bending it at a 90-degree angle toward the roof. This will give you the same measurement.
Step 3: Determine the Run
Determining the run is done by taking the numbers you calculated for the span and the rise. Take the total span divided by the rise. The resulting number will give you the run for the roof. Be sure to use similar units when dividing the span by the rise.
From these measurements, you will be able to determine the pitch of the roof. For example, a roof with a 120-foot span and 10 foot rise has a pitch of 1/12.
There are different pitches used on homes depending on where it is built and how exposed it is to rain and wet weather. A roof’s pitch determines the ease in which water will run off and not cause a leaking problem. Measuring it will give you an ideal of how steep it is and how well it handles weather related issues, such as rain and inclement weather.