Calculating the quantity of materials needed for a roofing job can be complicated, especially if the roof is complex. It can also be dangerous; some roofs are so complex that the only way to get an accurate estimate is to climb onto the roof and measure each plane separately. In addition to determining the quantity of shingles, you must also determine how much underlayment, drip edge, flashing and other products will be required. For all of these reasons, it is best to have a professional roofing contractor determine the materials needed for the job. However, if you are just trying to get a rough estimate, this roofing calculator may help.
Definition of Terms
Before continuing, it might be helpful to define certain terms used.
• A square is a measurement used in the roofing industry to indicate that the product will cover 100 sq. ft. of roof area.
• Pitch or slope is a measurement that defines how much the roof rises vertically for every 12 inches of horizontal distance. It is always expressed with the vertical rise first. To illustrate, if a roof rises 14 inches for every 12 inches of horizontal length, the pitch would be expressed as 14/12.
• The ridge is the horizontal area where the tops of two roof planes meet.
• The hips are the sloping vertical areas where two roof planes meet.
• Valleys are the channels where two roof planes meet.
Estimating Roof Area Using Pitch and Square Footage
If you are mathematically inclined or have a roofing calculator, you can estimate the roof area if you know the pitch of your roof and the square footage of your home. To illustrate, if your pitch is 4/12 and your two-story home has 1,400 square feet on each floor, these are the calculations.
• Divide the pitch. For a 4/12 pitch, the answer is 1/3.
• Square the above answer, which in this example would yield 1/9.
• Add 1, expressed as a fraction. That is, you would add 9/9 + 1/9 for a total of 10/9.
• Take the square root of 10/9, which is approximately 1.054.
• Multiply 1.054 by 1,400, the square footage of the home used in this example. You should get 1,475.6.
• Divide 1,475.6 by 100 to determine the number of squares required. You will need at least 14.756 squares of roofing. However, you should add about 10 percent for starter strips, valleys, waste and hip and ridge.
Estimating Materials Based on Actual Measurements
Measuring each roof plane requires you to actually go onto your roof. If your roof has a number of planes and numerous hips, ridges and valleys, this is the most accurate way to calculate the materials needed. Take a metal tape measure and a pen and paper. Measure each plane’s length and width. Record your measurements. Once you are safely on the ground, use your measurements to determine the square footage.
• For rectangular areas, multiply the length by the width. For example, if a plane measures 30 feet by 100 feet, this would be 3,000 square feet.
• For triangular areas, you may need to dust off your geometry book. If the area forms a right triangle, you can make use of the Pythagorean theorem. Otherwise, you might want to look up how to calculate the semiperimeter and then use Heron’s formula to find the area.
• Be sure to add extra for valleys, hips and ridges.
Estimating Materials Based on Decking
If you can see the plywood panels that comprise your decking, you can get a rough estimate by counting the number of panels. This requires that existing roofing has already been removed or that you can see the panels clearly from the attic. Most panels are 4 feet by 8 feet, making them 32 square feet. Simply count the panels; if they are not full panels, you may have to estimate their size. Multiply your total number of panels by 32 to determine the total number of squares needed. Add about 10 percent to allow for waste, hips, valleys and ridges.
Ask Alpha Roofing for an Estimate
As you can see, a roofing calculator can give you an idea of the materials for a roofing project; however, it’s complicated. Roofing contractors have different methods that can be used, so you really should ask a professional for help.
Alpha Roofing is an award-winning contractor serving Austin, Texas and surrounding areas. We offer a full range of rooftop services, including asphalt shingle installation and repairs, metal roofing systems and chimney repair. We also installsiding and skylights. Our crews are highly trained and work only for us. We are committed to providing quality work and outstanding customer service at affordable rates. Call (512) 777-1086 or complete the online form to request a free quote.
We service the areas of Buda, Kyle, Killeen, Cedar Park, Leander, Belton, Hutto, Tyler, Lakeway, Lago Vista, and Taylor, TX!
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