This article describes the basic math to calculate roof materials. If you have ever asked yourself "how many squares is my roof?" this article will help you find the answer. This article teaches you the math formula to figure out how much roofing and underlayment you need to order.
Roofing is talked about using the term "square", as in "This shed roof is 16 squares". A "square" refers to 100 square feet of roof or a 10 foot by 10 foot area. So a roof that has 1600 square feet of area has 16 squares. Remember that unless the roof is flat, the square footage of the building is different than the square footage of the roof. This is because of the pitch of the roof and the overhangs.
Determine the squre footage of the shed foot print by measuring the length and width of the shed including the overhangs. For example, if you have a simple 12 foot by 16 foot shed you add the overhangs to those dimensions. If the overhangs are 1'-0" then you have 2' extra each dimension. 14' x 18' = 252 sf. flat.
The roof pitch is the amount of slope. The slope is described by stating the "rise" in inches (how far up it goes) over the "run" in inches (how far horizontal it goes).The pitch is the part of the calculating roof problem that makes it a little tricky but keep reading the answers are here.
For this example we will use a 6 in 12 pitch. For every 6 inches the roof goes up to the peak it goes 12 inches horizontally. 6/12
6x6=36 (square of the rise)
12x12=144 (square of the run)
36 + 144 = 180
These are the sums and square roots for the most common shed roof Slopes:
3/12: 9 + 144 = 153 Square Root = 12.369
4/12: 16 + 144 = 160 Square Root = 12.649
5/12: 25 + 144 = 169 Square Root = 13
6/12: 36 + 144 = 180 Square Root = 13.417
7/12: 49 + 144 = 193 Square Root = 13.892
8/12: 64 + 144 = 208 Square Root = 14.422
10/12: 100 + 144 = 244 Square Root = 15.620
12/12: 144 + 144 = 288 Square Root = 16.970
13.417 / 12 = 1.118 (1.118 equals the product)
Our area from step 1 was 252 sf of flat roof so:
1.118 x 252 = 282 square feet
282 / 100 = 2.82. Round this number up and thats your answer, 3 squares!
Add 10% to this number for waste and it is 3.3 squares.
There you have it, the simple formula to calculate shed roof materials. Now is the fun part, ordering it and installing it on your backyard shed. See our articles on how to install different types of roofing.related articles