| Measuring your roof
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| In order to estimate how many shingles you'll need, first you need to estimate the total square footage of your roof's surface. Just 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. Simply add the square footage of each of the planes together to derive the total square footage of your roof.
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| 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 24,000 square feet by 100. Which means you will need 240 "squares" of shingles to cover it. The most common type of shingle, called a three-tab or strip shingle, is generally packaged three bundles per square.
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| If this is a new roof, you will also need 240 squares of underlayment (no underlayment is needed if you are applying shingles directly over an existing asphalt roof). Underlayment usually comes in rolls of four squares each, so covering 240 squares would require 60 rolls of underlayment.
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| Be sure to add 10% to all of your material totals for trim allowance.
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| You will also need to know the slope of your 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.
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| To measure a steep roof, you will have to use an alternate method. To obtain the roof length, measure the exterior walls plus the overhang for the length of the house parallel to the ridge. Next, throw a rope over the ridge and mark it on each eave. This will give the width dimension to use in figuring your area. This should be done on each roof section containing a horizontal ridge.
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| Too much work? Or can't get up on roof? Click here for a free quote and we will send a roofing contractor to do this for you.
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