Math for Roofers

You call the roofer in Arrowhead to fix that slow leak and you learn that what you thought would be a simple roof repair is going to require a lot of work. You hear the price and you about fall over. It’s going to be how much?

Roof work requires experience and skill to get right, whether you are looking at a simple repair or a whole new roof installation. Not only are you paying for the high quality of workmanship that experience and skill produce, but you are also paying for time and materials. Understanding the math that roofers used to arrive at their final charges will help you understand why things cost what they do.

math for roofers

Here’s a look at some of the math that roofers have to use when doing their work and when providing estimates and final bills:


According to companies like the Nimbus Roofing of McKinney TX, geometry is very important when designing roof framing. Roofers have to use it when constructing a frame for a new roof or when repairing a frame.
In particular, roofers have to use geometry to determine the length and the angle to which to cut the rafters. They have to do this with a formula that takes into account the rise of the roof (the vertical height) and the run (the horizontal length). They use a formula to determine the length of the rafter that will complete the triangle, and then they use a formula to determine the angles in the triangle so they can make the right angled cuts.

roofer using geometry math for layout of roofThese calculations can become quite complex depending on the shape of the roof. Some roofs will require multiple rafters at different angles to provide the right support, and different calculations have to be used for each of these rafters.


Pitch is a simple ratio of the rise to the run of the roof. The pitch is the number of inches the roof rises compared to every 12 inches of horizontal run. Therefore, if a roof rises four inches for every 12 inches of horizontal distance, it has a 4-in-12 pitch.

Roofers use the pitch to determine what kind of support is needed for the roofing material and what kind of measures need to be taken to deal with water runoff. For example, roofs with a steeper pitch may need additional support for heavier roofing materials. Roofs with a lower pitch may need additional measures for water elimination.


roofers using math to calculate materials for roofDetermining load is a very important part of a roofer’s work. Load refers to how much weight a section of roof can bear, and it is determined in pounds per square foot.

To determine load, the specific area of the roof that needs to be tested must be identified. The roofer then has to determine the weight of each of the components. For example, if you are considering re-roofing with slate, the roofer will need to know the weight of the slate per square foot, as well as the weight of the underlayment, substrate and miscellaneous materials like glue and nails. The roofer then has to determine how much weight the rafters and other support beams can bear.

If the current roofing support cannot bear the load of the new roofing materials, new beams must be installed that can bear the weight. Depending on the size of the roof and the weight of the new materials, steel beams may even need to be used.

roofers using math to determine their load size for roofingCalculating Materials

Roofers have to do a lot of calculations to figure out quantities for materials.

For example, say you are getting an estimate for re-roofing. The roofing contractor in Arrowhead has to determine the surface area of the roof, which requires multiplying the height and the width of each square or rectangle. This can get more complicated when the roof meets at different angles that do not make perfect square or rectangles. You see this where a gable meets the main pitch of the roof usually.

Once the square footage is calculated, the roofer then has to buy enough materials to cover the whole area, which requires knowing the square footage of individual tiles or shingles and figuring out how many of each are needed. The roofer will do the same for calculating how much underlayment and other materials are needed.

As you can see, complex calculations can go into determining how much materials are needed for any specific roofing job.

Canyon State Roofing and Consulting in Arizona hires only the best and most experienced roofers. With their extensive training and experience, they are able to make fast and accurate calculations so you know what to expect. We are dedicated to providing the highest quality of workmanship, whether we are performing a simple roof repair in Arrowhead or a new roof installation. Call us in Arizona today to get a free estimate or to learn more about our services.

Published By:

James McLain Owner and Phoenix Roofing Contractor at Canyon State RoofingCanyon State Roofing

4809 E. Thistle Landing, #100
Phoenix, AZ 85044

Office: (602) 400-1635

Published On: December 19th, 2016Categories: Repair

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