Figure Out Your Homes Footprint
If you use the square footage of your home, youll only get a vague idea of what the square footage of your roof is. Thats why you have to figure out your homes footprint.
A person of average height will have a stride somewhere between 2 to 2.5 feet. To figure out your homes footprint, you can step off the dimensions of your roof by counting the steps you take to get the length of your home. You will then step off the width of your home.
After stepping off the length and width of your home, youll multiply the two numbers to get your homes footprint.
Length x width = your home’s footprint
Your calculations are going to be off, but measuring this way can give you a basic idea of your homes footprint. Keep in mind, square footage of a house does not equal the square footage of a roof.
How To Figure Out The Square Footage Of A Roof
Repairing or replacing your roof can be expensive, especially if you dont know how to calculate its square footage. A wrong estimate can cost you thousands of dollars and might even delay your roof repair, leaving your home exposed to the elements. The good news is you can easily estimate the square footage of your roof with a few tools and basic geometry.
Finding The Total Roof Area
Once the area of the roofs footprint is known, the overall roof area can be found by accounting for the roofs pitch. The pitch of the roof is the rise over a 12-inch run. Use our roof pitch calculator to find the pitch of your roof.
Next, multiply the footprint of the roof by the multiplier below for your roof pitch to find the overall roof area.For example, a 4/12 pitch roof that is 100 square feet:
100 × 1.054 = 105.4ft2
Roof Pitch Area Multipliers
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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.
Calculating How Many Shingles You’ll Need
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How To Measure A Roof For Shingles
A home’s roof is measured in squares. As you prepare for your roofing project, you’ll use squares to determine the amount of roofing materials you need, from asphalt shingles down to the underlayment.
How To Measure A Hip Roof Hip Roof Hip Roof Design Roof Truss Design
- The shingle gauge is a handy device for property owners and managers, as well as insurance claims adjusters, roofing contractors, and home inspectors.
How Shingle Quantities Are Measured
Roof shingles are sold by both the bundle and by the square. A square of shingles is the quantity needed to cover 100 sq. ft. of roof. Shingles are packaged in paper- or plastic-wrapped bundles designed to be light enough for a person to carry, so heavier shingles require more bundles per square. Three bundles to a square is most common, which applies to most three-tab strip shingles and some lightweight laminated shingles. Heavier three-tabbed shingles and laminated shingles require four, or sometimes five, bundles to cover a square. When shingles come three bundles to the square, there are 29 standard-sized shingles in each bundle.
Figuring out the roof area is the first step to determine how many bundles youll need to order. There are two ways to size up a new or freshly stripped roof: the measurement method and the sheet-count method. Theres a third method for calculating bundles when youll be laying new shingles over old or if the old roof is still in place.
Once you have a bundle or square count for the main roof area, youll add additional shingles to account for waste, starter shingles, and extra shingles for hip and ridge caps.
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Calculating The Area Of A Complex Roof
Areas of complex roofs with multiple hips and valleys take the most time to calculate. Start by making a rough sketch of the roof. To simplify the calculation, break down the sketch into rectangles and right triangles , then take as many measurements of the roof as you can to match the sides of the rectangles and triangles on the sketch.
Use visual cues from the existing roof shingles or roof sheathing to determine square lines off eaves edges or ridges. These cues will help you measure the lengths of the sides of the rectangles and triangles. For instance, the cutout slots on shingled roofs run perpendicular to the eaves, and nail rows in sheathing are pretty close to square also. It is difficult sometimes to get accurate measurements. Dont get too concerned though just round lengths to the nearest 6 in.
With the sketch filled in with measurements, you can determine the size of the roof area. The area of a rectangle is length multiplied by width, whereas the area of a right triangle is the length of the two sides that meet at the 90-degree corner multiplied together and divided by two .
Tally the square footages of all the rectangles and triangles, which will give you the total square footage for the roof. The example here shows the calculation for a roof with two hips.
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 of your home 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.
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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.
Plan For Waste Factor
The only roof that will generate no waste from cutting is that rare simple gable whose roof length is divisible by the 3-ft. length of a shingle. Other simple gable roofs will require cut shingles at the rakes. From there, the waste factor increases with every obstruction, such as a chimney, and with every hip or valley.
Laminated shingles typically generate less waste than three-tab shingles do because you dont have to maintain a cutout pattern, but its tricky to determine exactly how many square feet of shingles you will be able to salvage. Its best to plan your order using the same waste factor that you would use for three-tab shinglesat worst youll just have a couple of bundles to return.For a simple roof, I generally figure 1 percent as a waste factor. On a complex roof with open valleys, I add 5 percent and sometimes more. Theres no calculation you can use to determine the extra shingles youll need for waste. With experience estimating jobs, youll get a feel for how many extra shingles to order.
Waste is also generated when shingles are damaged, which is inevitable when youre moving shingles around a steep roof slope and some will slide off. You may be able to salvage part of the damaged shingle, but dont count on it. You can also waste shingles when you nail them improperly and have to remove them. You may drive nails too low in the exposure or fasten one off a control line.
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Calculate The Amount Of Asphalt Or Fiberglass Shingles Needed To Cover A Hip Roof
A hip roof’s square footage is equal to that of a gable roof with the same dimensions. The difference is in the amount of ridge capping you need and the amount you will waste. The top ridge will be shorter for a hip roof, but the 4 hips will add to the amount of ridge capping needed and because of the angles the amount of waste will be higher than for a similar sized gable roof.
As a note:
But with all the different types available, not all packs are equal in the amount of pieces they contain, the length of the individual shingle and the square foot coverage per pack. Not all types of shingles can be used for the starter strip and the ridge capping needed or you could be using ridge caps to cover the top ridge and the hips. That is why this calculator requires “the square foot one pack will cover” and the results for starter strip and ridge capping is in lineal feet needed for those two items and is not included in the Total Packs Needed.
Calculate The Roof Area
Now that you have all of your roof measurements, you can calculate its surface area. Simply multiply the length and width of each rectangular plane, and then add the combined area of the hips. Then multiply this number by the roofs slope factor, and then multiply this final result by 1.10 to allow for error.
In this example, our imaginary home’s hip roof would cover a surface area of + , while the lean-to roof would be equal to . This gives you a total surface area of 935 square feet. Multiplying this by the slope factor of 1.03 equals 963.05 square feet. Multiply this by 1.10 to obtain 1059.4, which is a good estimate of your roofs surface area.
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Final Thoughts On Measuring Your Roof
If youre looking for a simple ballpark estimate of your roofing materials needs, Google Earth really does a great job of quickly allowing you to measure the square footage youll need to cover. While its technology sure is surreal, it has drawbacks in its ability to precisely measure distances represented in 3D. Therefore, it can be helpful to gauge estimates of your materials costs by measuring from the ground and on top of your structure. As always, if youre feeling confused, dont hesitate to get in touch with a local roofing contractor to help you out. Many will provide estimates for free. Simply ask how many squares of material they estimate youll need, and compare that to the results you got from using any of the methods we outlined above.
How To Calculate Number Of Roofing Shingles
Fortunately, you don’t have to make a haphazard shingle estimate when planning for your roofing project: your roof size and chosen shingle type will guide the purchase process.
Shingles are sold in prepackaged bundles, not individually. Roofing manufacturers take the guesswork out of how many bundles you need per squareit’s listed in the specifications of each shingle they make. The specs for any given shingle will tell you how many bundles make up a square, how many shingles are in a square, and even the approximate number of nails you’ll need per square.
Often, three bundles of prepackaged asphalt shingles make one square, as is the case with the Timberline® HDZ Shingles. That said, the number of bundles you need can vary depending on shingle design. For example, five bundles of architectural asphalt shingles with artisan-crafted shapes, such as the Grand Sequoia® Shingle, cover one square. Once you know the number of squares of material your roof needs, check the shingle manufacturer specifications so you get your hands on exactly what you need.
If you’re still deciding on the perfect shingle for your roof, play around with the GAF VirtualRemodeler. The free online tool helps you envision how different shingle colors and styles would work with your home’s style. Be sure to keep local building codes in mind as you weigh your shingle options..
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How To Measure Your Roof With Google Earth
Using your computer to get a ballpark estimate of your roof area is easy and fast. However, using satellite imagery may not be an ideal solution if your structure is in a very remote location that hasnt been 3D scanned. Thats because well need to grab an accurate representation of your roofs pitch for measuring purposes. From above with a 2D image, everything looks flat. If you were to just measure your roof area from directly above, you wouldnt be accounting for its pitch, or slope.
Consider two homes with the same base area square footage, but one of them has a much steeper roof pitch than the other. That structure would need to be taller, and there would be a lot more roofing material to account for. If youre just measuring from above in 2D, both of these structures might look identical. If you dont account for roof pitch, youre going to underestimate your materials requirements, which could be a costly mistake.
Satellite technology has progressed a lot in the past few years. With , you can easily find your address and a 3D replica of your structure, including your roofs pitch. Lets get to it.
Once you load the site, youll be presented with our beautiful planet:
While you can switch to 2D mode by clicking the button in the lower right, youll want to stay in this 3D view so you can get a good view of your roofs pitch.
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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How Do I Measure A Steep Roof
Most roofers wont go on a roof with an 8/12 roof pitch or greater with special equipment such as scaffolding and roof jacks and neither should you. Instead, use one of the four methods described above that allow you to measure the roof while standing safely on the ground or from the comfort of your computer.
While these methods may not be quite as accurate as taking actual measurements from the rooftop, theyre close enough for calculating how many shingles youll need to purchase for a new roof.