How To Calculate Roof Area
A careful accounting of each section of roof surface, called a plane or facet, is necessary for an accurate estimate.
As measurements are taken, keep in mind that every dormer facet also needs to be measured and added to the area, less the footprint of that dormer.
Measure the footprints of all dormers, pipes, chimneys, and skylights. These dimensions can be subtracted from the total area as you calculate the squares. The measurements of each of these features are important to track! Each of these roof features has additional considerations later when calculating the repair or replacement cost of your roof.
Keep in mind every roof plane may not be in the shape of a rectangle or square. Each shape, whether it is a rectangle, square, trapezoid or rhombus, has a specific calculation to determine area. To more easily calculate the area, each facet can be separated into basic geometrical shapes. Be sure to keep track of each shapes measurements and pitch.
Now, it is time to calculate the total area.
How did your roof measure up?
Measure The Footprint Of The House
The footprint of a house is a bit different from square footage because it refers to the perimeter of the exterior walls at ground level.
Image credit: Aluminum Lock Roof Inc
Square footage, on the other hand, includes the entire area of the house within the walls, including additional stories. Since you only need one roof regardless of whether its a one-story or three-story house, the footprint is a more accurate starting point than square footage.
To measure the footprint, use a tape measure or wheel and measure the length of each side of the house. Be sure to measure all the way out to the roof overhang, as you can see in the picture above, since thats where the roof ends.
Also, make sure to include any additions to the house like sunrooms, garages, or other bump-outs. As you measure, record your findings on your diagram so that you know which measurement corresponds to which side. This will be important in the next step.
Why Should I Measure My Own Roof
If you plan on re-roofing your own home then you will need to calculate materials so you wont waste your own time and money. If youre like most people, youll need to hire a professional.
Knowing your numbers will help you figure out what roofing materials are within your budget and having your square footage handy is a great way to protect yourself from inflated quotes.
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Draw Each Shape Individually Calculate Each Area And The Total Square Footage Of Your Roof
Now we have eight shapes to find the area of six triangles and two rectangles. Instead of breaking out the old textbooks to calculate triangle areas, we like to use a triangle calculator. It makes figuring out the area of triangles a lot simpler.
In the example above, we have two triangles with sides of 30, 20, and 20 feet. Pop those figures in the three-sides calculator and youll get an area of 198. Since we have two of those triangles, multiply by 2 for a running total of 396 square feet.
We have four remaining triangles, all with dimensions of 15, 20, and 25 feet. That same calculator reveals a result of 150 square feet. Since there are four of those triangles, multiply by 4 to get 600 square feet.
Lastly, we have two rectangles of 15 by 30 feet. This one is easy, just width times height for a total of 450 square feet for each one. Multiply by 2 and their total square footage is 900.
Adding all the areas up yields a total of 1896 square feet . Since roofing material comes in 100 square foot squares, youll need at least 19 of them for your roofing project. Itd be wise to get at least 20 to account for mistakes and waste.
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How To Measure A Roof Using Google Earth
If youre looking for a free way to measure your roof using imagery you can find on a smartphone or computer, consider logging into Google Earth and searching for your home. If you live in a large enough metropolitan area, youll find both the 2D and 3D imagery needed to take roof measurements online.
Begin by entering your address into Google Earths search function. Youll get a birds-eye 3D view of the property, which will allow you to get a good view of the roof pitch. Position the view, so youre looking down on the roof.
Use Google Earths area measurement tool to outline the section of roof you want to measure, making sure to set the display to feet. Once you create a box, Google will tell you the length of each side and the total square footage.
You can use that number with the slope factor of your roof to come up with a fairly accurate estimate.
This method isnt as precise as the expensive apps, but it will give you a good enough estimate of the square footage of your roof to purchase shingles.
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Find The Area Of The Roofs Footprint
Determine the area of the roofs footprint, which is the area covered by a roof regardless of slope .
Google Earth Pro makes finding the area of a roofs footprint pretty easy with the measuring tools they have available, but you can also simply measure the dimensions of the building on the ground and figure out the area that way .
Dont forget to take into account overhanging eaves or any other areas where the roof extends beyond the exterior walls of the building.
You will also need to increase your total footprint area to include any areas where one roof section overhangs another roof section. Youll probably be trying to estimate the entire area of a roof.
How Many Roofing Shingles Do I Need
To estimate how much roofing material you need, such as bundles of architectural shingles or rolls of synthetic roofing underlayment, you need to know the total square footage of your roofs surface.
How to Calculate Total Square Footage of Your Roof
To find your roofs total square footage:
Example #1: Shed Roof with One Roof Plane
For example, this shed roof has one roof plane.
Multiply length times width :
A x B = 40 x 30 = 1200 sq. ft. for the total square footage of the roof.
Example #2: Gable Roof with Two Roof Planes
This gable roof has two planes.
So to derive the total square footage of the roof, you would:
Ready to get an estimate? Find an independent roofing contractor in the Owens Corning Roofing Contractor Network near you.
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Keep The Slope And Complexity Of Your Roof In Mind
You have to keep in mind the makeup of your roof when doing the calculation for the square footage. The steepness and complexity will change the number you multiply the footprint by.
For an easy up and over, walkable gable roof, youll multiply the footprint of the roof by 1.3 to get the square footage of your roof.
For a hip roof with a low slope, you’ll multiply the footprint of the roof by 1.4 to get the square footage of your roof.
For a steep and complex roof, you’ll multiply the footprint of the roof by 1.6 to get the square footage of your roof.
How To Measure The Perimeter Of A Sloped Roof
The perimeter of a hip roof or a hip and valley roof run horizontally to the ground. Take a look at image 1.16 and image 1.17 for a visual example for better understanding. You can determine the length and width by simply using the dimensions from the roof plan. Therefore, you can find the perimeter of a hip roof or a hip and gable roof by using the same formula used to find the perimeter of a flat roof.
Perimeter = 2
If the building has no recesses the the formula is:
Perimeter = 2
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Calculate The Number Of Squares On The Roof
A square on a roof is any area that measures 100 square feet. After determining the square footage of each plane on the roof, you will want to determine the number of squares, which are the units commonly used for roof measurements.
Calculating the number of squares on a roof is simple. Just divide the total square footage of the roof by 100 to get your answer. With this number, you can estimate how much roofing material you will need for the project.
Measuring A Roof From The Ground
Measure out from the face of the wall below the fascia or rafter tails to a point that aligns with the outer edge of the roof. Multiply this measurement by the length of the roof from end to end, and add this to the first result. Double the result to determine the total area of the roof at both sides.
Measuring your roof is the first step in a successful re-roofing project. You can actually get an estimate of your roofs measurements from the ground if youd rather not climb a ladder and get up on the roof yourself. Otherwise, you can climb up onto your roof to take more accurate measurements. Either way, weve got you covered!
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What Kind Of Roofing Do You Need For A Gabled Roof
Unsubscribe at any time. Clay or concrete shingles, bituminous shingles, metal shingles, and cedar are some of the roofing materials you can use for a gable roof. While a 40° angle or a 10/12 slope is recommended for snow-covered areas, using metal shingles or vertical joints can help prevent leakage if the roof is sloped or sloped.
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Tips For Getting Started
Tip 1: Measuring to the nearest inch along eaves and across gables can be done from the ground just dont forget the overhang.
Tip 2: If you know the dimensions of your previous asphalt roofing job, you can use this info to cheat a little. Typical 3 Tab asphalt shingles have tabs that are 1 foot wide with a vertical exposure of 5 inches. Make sure to physically verify these dimensions by measuring 4 or 5 courses. Counting the shingles can give you eave to ridge dimensions from the ground.
Tip 3: 100 Square Feet = 1 Square in Roofing Terms
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What Is A Bundle Of Shingles
A package of roofing shingles is called a bundle.
How many bundles of shingles per square?
3 bundles = 1 roofing square
So in the 2400 square foot gable roof example, you would need 72 bundles of shingles .
Here are a couple more examples:
What Is Slope Factor
Taking a 2D measurement of a roof either online via Google Earth or by measuring the exterior walls of the home doesnt account for the elevation of the roof, which adds square footage. Slope factor is a convenient way of using the pitch of your roof to convert a 2D measurement to an accurate measurement of the roofs square footage.
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Whats Your Roof Slope
You will also need to know the slope of your deck.
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 mentioned second.
The Positive Roof Measuring Method
The positive roof measuring method requires you to break the roof up into measurable sections. For image 1.2 find the area of all sections of the roof, and then add them together to find the total area of the roof.
Area of section A = 20 x 60 = 1200 sqft
Area of section B = 20 x 40 = 800 sqft
Area of section C = 20 x 20 = 400 sqft
Therefore, the total area of the roof plan above is 1200 sqft + 800 sqft + 400 sgft = 2400 sqft
Multiply The Slope Factor By The Number Of Roofing Squares
Ok, so now we know the slope of the roof but we need to find the slope factor to figure out how many more roofing squares we need. Fortunately, lots of roofing companies share this information online. You can see the chart above from Everlast Roofing as an example.
Image credit: Everlast Roofing
So, going back to our roof with a 4:12 slope, you can see that the corresponding slope factor is 1.0541. To find what this means in terms of roofing squares, you would do the following calculation:
9 roofing squares x 1.0541 = 9.4869 roofing squares
Experts Guide On How To Measure A Roof
If you dont have the building blueprints and are working on a roof renovation, you can estimate certain expenses by taking preliminary measures from the ground. Measurement of hip roofs, dormers, or hillside residences needs skill and specialized equipment from the ground level.
Let me reveal one of the best-kept secrets anyone should know when learning to measure a roof without getting off the ground. If you arent a home roofing company owner, you probably havent heard of this. Its a fast and safe technique to calculate the size of just about any kind of roof.
So please continue to read our article to learn more about how to measure a roof, and then you’ll be able to move on to How to Build a Roof!
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The Negative Roof Measuring Method
To find the area of a roof using the negative roof measuring method you will extend the roof line past the roof to form a single rectangle. You will then subtract the rectangular areas that lie outside of the roof.
First you need to extend the roof lines to form a single rectangle.
60 x 60 = 3600 sqft extended rectangle
You then need need to find the area of the rectangles outside of the roof area. You can see in Image 1.3 that the areas outside the roof layout are sectioned off into section A and section B. We will find the areas of these sections and then subtract them from our extended rectangle.
Area of section A = 20 x 20 = 400 sqft
Area of section B = 20 x 40 = 800 sqft
The total area outside of the roof layout is 800 sqft + 400 sqft = 1200 sqft.
3600 sqft 1200 sqft = 2400 sqft
You can see that using the negative roof measurement method gives us the same result as the positive roof measurement method.
How To Measure A Hip Roof For Shingles
Hip roofs have four faces or sides, so they are different from common peak roofs. Heres the guide to measure shingles on the hip roof:
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Calculate Roof Pitch From The Ground In Three Quick Steps
Roof pitch is one of those things that middle school math and geometry instructors can easily point to, and say, See? Learning how to work with rise over run is fun and useful, right? If at any moment you start having PTSD flashbacks to algebra or geometry class, take a deep breath. Well walk you through this slowly in three simple steps. All you need is a tape measure, and possibly a helper to hold it.
Step One: Grab that tape measure, notepad, and pencil and head outside. Find the slope of your roof youd like to measure, and start measuring the distance from the outer edge of the eave to the point at which the plane of the roof slope is barely visible to your eye. Write that number down in both inches. This figure is the horizontal run.
Step Two: Stand directly underneath the gutter or edge of the roof plane you want to calculate the slope for. Measure the distance from your eye to the top of the drip edge of your roof overhang. Write that number down in inches, too. This figure is the roof rise.
Step Three: Take the roof rise figure in Step Two and divide it by the horizontal run from Step One. In the example above, the rise is 60 inches and the run is 120 inches. This reduces down to a roof pitch of 6/12. Well use this figure in just a bit, so keep it handy.