Tools
Measuring for your new roof is easy. To determine how much roofing you will need, follow these simple steps:
In order to estimate how much roofing you will need, you must first estimate the total square footage of your roof’s surface. Measure the length and width of each plane on the roof, including dormers. Then, multiply length x width to get the square footage of each plane. Then add the square footage of each of the planes together to derive the total square footage of your roof.
For example, this shed roof has one roof plane. Simply measure length (A) x width (B): A x B = 12′ x 10′ = 120 sq. ft. for the total square footage of the roof.
In this example, the gable roof has two planes. So, multiply length (A) x width (B) to get the square footage for each plane, then add the two planes together to derive the total square footage of the roof:
Plane 1: 12′ x 10′ = 120 sq. ft.
Plane 2: 12′ x 10′ = 120 sq. ft.
Plane 1 + Plane 2 = 240 sq. ft. for the total square footage of the roof.
Be sure to write down the perimeter length of the roof in order to estimate drip edge, ice and water barrier, and more. Also note valleys, ridges, chimneys, vent stacks, and skylights.
You will also need to know the slope of your roof deck. In order to determine this, measure the vertical rise of your deck in inches over a 12″ horizontal distance. If this rise is 4″, then your roof slope is 4 in 12. Roof slopes are always expressed with the vertical rise mentioned first and the horizontal run (12″) mentioned second.
Roof surfaces are measured in “squares.” A “square” is an area of roof which measures 100 square feet. To determine the number of squares on the gable roof above, for example, simply divide its total of 240 square feet by 100. Which means you will need 2.4 “squares” of roofing to cover it. Shingles are sold in bundles and depending on the type and brand of shingle you purchase, it may take a different number of bundles to make a square. When shopping for shingles, you should remember to compare cost based on squares and not bundles.
Metal roofing is sold by the sheet/panel. To determine the number of sheet/panels you will need to cover your roof, you should divide the width of the roof by the sheet/panel coverage width.
Most other types of roofing are sold by the square foot. If you need assistance in determining how much roofing you will need, stop into your local Curtis Lumber.
