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HomeHow to Accurately Estimate the Size of Your Roof

How to Accurately Estimate the Size of Your Roof

How to Accurately Estimate the Size of Your Roof

Looking to Replace Your Roof? Things to Consider


Your roof is an important structural component of your home. Thinking about getting a new roof requires an investment of time and resources. One of the first steps in taking on a new roof or repair project is estimating the size of your roof to help you determine what material to use, and how much you will need. It should be easy to estimate the size of your roof.


You know the square footage of your home, so from the info you can determine your roof size, right? Well, there are many factors to take into consideration when you estimate the size of your roof. There are slopes, different area sizes, and much more to think about. Let’s walk through some basic techniques that will help you estimate the size of your roof.

Estimate Total Square Footage

This is the first step in getting accurate size dimensions for your home’s roof, and this step is easier than you may remember from math class! Just measure the length and the width of each plane of your roof. After you have those numbers multiply your length x width to get the square footage of each plane. Then you take each plane’s square footage and add those numbers up to get the total size of your roof.

For example, this diagram shows one plane for the entire roof. So this calculation should be easy. Just measure:

Length (A) x Width (B) = Total SQ. ft.

If you had a roof with multiple planes, like the one shown to the right, then use the equation above to solve the square footage for each plane. After that add all the sides together.Info graph on determining roof size when there are multiple planes

plane 1: A x B = Sq. Ft. plane 1

plane 2: A x C = Sq. Ft. plane 2

plane 1 + plane 2 = Total Sq. ft.

Squares

Now you have the square footage of your roof. However, roofs are often measured in just “squares.” Luckily, it is very simple to go from square feet to squares. A square is an area of a roof that measures 100 feet. So to get from square feet to squares just take your total sq. ft. and divide that number by 100. If your roof is 20,000 square feet then your roof is 200 squares.

What does this mean? You can estimate that it will take 200 squares of shingles or other roofing material to cover your entire roof. A very common material is a three-tab or strip shingle. This specific type of shingle is typically purchased in three bundles per square.

Underlayment and Other Material Consideration

Shingles or other roofing material is important and probably the main reason you needed to estimate the size of our roof, but you will also need to take into consideration that a new roof will require the same amount of underlayment

This means if you needed 200 squares of shingles, you would need that area’s worth of underlayment. Underlayment is found in rolls of 4 squares each. This means that covering 200 squares of shingles is equivalent to 50 rolls of underlayment. However, if you are putting shingles on an already existing asphalt roof then you do not need to lay down additional underlayment.

You can expect there to be about 10% of the material that needs to be trimmed off after all is said and done. So make sure that when you have the size of your roof estimated that you account for 10% of the extra material.

For example, if you need 200 squares of shingles and 50 rolls of underlayment to fit your roof, you will actually need to purchase 220 squares and 55 rolls to account for the excess material that will be trimmed and thrown away

Slope

Since slope was mentioned above you are probably wondering how that ties into getting a proper size estimate for your roof. It isn’t so much about the total square footage as much as its importance if you're trying to determine if you want to have a new addition to your home, install skylights, or cut some new rake boards.

The slope is often referred to as the angle, or pitch, of a roof and is calculated by the number of inches it rises vertically for every 12 inches it extends horizontally. So for a roof that rises 10 inches for every 12 inches of a horizontal run has a 10-in-12 pitch.

The slope is often referred to as the angle, or pitch, of a roof

Roofing Calculators

You mean there are free online tools that can do this math for me?! Well of course! The internet is famous for shortcuts. But isn’t it rewarding to solve these problems on your own?

Now you know exactly what goes into estimating the size of your roof and the thought process behind some key decisions you will face when speaking to a roofing contractor. You have all the information necessary, but now that you know the madness behind the method, here is a great roofing calculator to save you some time and energy.

Or better yet, you can talk with one of our professionals at service.com who can give you a proper estimate of the size of your roof and the cost of repair or replacement. Get a quote today!

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