How To Calculate Roof Rise

The total roof rise is the total vertical height of the roof. Typically this amount is determined by a measurement from the midpoint of the roof to the ridge of the roof, which is the highest vertical point. The midpoint is the horizontal center of the roof. If you are a carpenter or builder, you may need to know the roof rise before it is up to be measured. Fortunately, you can calculate the rise of the roof using your building blueprints.

Step 1

Check with the designer to get the unit rise for the roof, which is the slope of the roof. The roof slope is the horizontal angle of the roof. This varies by designer because it can be any amount the designer wants. If you have blueprints directly from the designer, the unit rise should be listed for the roof. For example, assume the unit rise from the designer is six inches. A six-inch unit rise means that the roof rises six inches for every 12 inches, which is the standard roof cutting basic unit of measurement.

Step 2

Measure the span of the building, or consult your blueprints. The span of the building is the total width of the building. Once you have the span, divide it by two to determine the total run of the building. The run is the horizontal distance of only a section of the roof. Since a standard roof has just two sides, the run is half of the span. If you have a non-standard roof, such as an unequally pitched gable roof, the span will be divided by the total number of sides. For example, assume you have a standard roof and the span of the building is 26 feet. That leaves you with a total run of 13 feet.

Step 3

Calculate the roof rise using the figures for unit rise and total run. Multiply your figure for unit rise by your figure for total run to get the total rise. Using the example, it would be six inches times 13 feet. The total roof rise in the example equals 78 inches.