Roof Estimating Multiplier

When you are measuring your roof, you must always take into consideration the pitch of the roof when estimating for materials.

Roof estimating multiplier.

Multiply the footprint square footage by the multiplier for your roof pitch to find the actual square footage of the roof. That means that the roof surface area is 1.202 * 180 = 216.36 square meters. In our example, the multiplier for a roof pitch 8/12 is 1.202.

Multiply the area by the rafter multiplier that corresponds with the roof slope of your plans. Using this program, we can take any input (back of the napkin sketches, blueprints, aerial imagery, etc), and produce an estimate. For example, a 24 x 48 home with a 6:12 roof would calculate as follows:

Don’t forget to account for a waste factor as. Some of our popular posts. As a shortcut, the roof slope multiplier for any slope can be determined by finding the square root of ( (rise/run)² + 1).divide the rise by the run.

A 12/12 pitch roof uses a multiplier of 1.4142. How to estimate the roofing materials needed? For example, if you’re working on a house that is 30 ft.

Simply take the ground dimensions, multiply length times width (include overhangs) and multiply by the roof pitch multiplier. Measure the length and width in feet, then multiply together to find the square footage. This would be a roof with a pitch of 3:12 to 5:12, which means the roof rises 3 to 5 feet for every 12 feet of base horizontal length.

Identify the multiplier that corresponds with the roofs slope. Take the external dimensions of the house and divide it by 100. This is just the flat area.