In an ideal world, you would always be able to get an accurate calculation for how much material you will need for a re-roof before writing up a quote, but that isn’t always the reality. In times where you don’t have the time or means to get an exact idea of the amount of material you’ll need, it helps to have a process that will help you quickly and reliably estimate the size of the roof and the amount of material you will need to get the job done. This will help you give a more accurate quote to your customer, and help you gain a better idea of what kind of job you’re getting into.
Step 1: Calculate Roof Pitch
The roof pitch can be calculated by determining the number of inches in height change over the distance of one foot. So, if over a distance of one foot, the roof increases in height by four inches, your roof pitch would be 4:12, as it increases in 4 inches over a 12 inch distance.
Step 2: Divide the Roof Pitch by Twelve
Dividing by 12 gives the ratio of inches in rise per distance. Following our above example, you would divide the pitch of 4 by 12 and reach 0.33.
Step 3: Square the Result
Multiply the number by itself. Following our example, you would reach 0.1089.
Step 4: Add 1, Then Take the Square Root
Add 1 to the number, then take the square root. Following our example, adding 1 would put you at 1.1089, and the square root of that would be 1.053. If you’re not math savvy, you can use this square root calculator to assist you.
Step 5: Multiply the Square Footage of One Floor of Your Home
Multiply the square footage of one story of your home by the number you just calculated above. If one storey of your house has a square footage of 1,500, multiply that by 1.053 to reach 1,579.5, meaning you will need roughly 1,579.5 square feet of material for your roof.
This is a fairly simplified process that works best for simple roofs, but it can still be used for more complex roofs with multiple pitch angles. All you need to do is section off the roof and use a different square footage for each roof section and roof pitch. Of course there are more accurate ways to calculate overall roof size and materials needed, but this simple process will surely help you in a pinch when you need a fast and easy way to estimate roof size.