Once you’ve measured the building’s walls, estimate the length of the overhangs on either side (if your roof has them). The easiest way to do this is to simply eyeball them and approximate how long each one is in feet. Add these figures to your recorded measurements to account for the additional area. Estimating the area from ground level is less precise than measuring each side individually, but it can make a quick, easy, and safe alternative when redoing a square or rectangular roof. To measure an irregularly-shaped roof, you’ll need to get on top.
Pitch is expressed as “X-in-12 (inches)”. If you’re using a 1 ft (0. 30 m) level, the pitch is the distance between the edge of the level and the roof’s surface. A distance of 7 inches (18 cm), for example, would mean your roof has a pitch of 7-in-12. If you’re using a 2 ft (0. 61 m) level, divide the distance between the level and the roof by 2 to get the true pitch. A 14 in (36 cm) difference, for example, indicates a pitch of 7 in (18 cm). [3] X Research source The terms “pitch” and “slope” are sometimes used interchangeably when describing roofing projects.
For example, a roof with a rise of 3-in-12 will have a pitch multiplier of 1. 031, while one with a rise of 8 in 12 will use a multiplier of 1. 202. You should be able to pull up a number of reliable pitch multiplier tables with a quick Internet search.
If your roof measures 48 feet (15 m) x 24 feet (7. 3 m), multiplying its length by its width would give you a square footage of 1,152 square feet (107. 0 m2). If its pitch is 6-in-12 (a pitch multiplier of 1. 12), multiplying 1,152 sq ft (107. 0 m2) by 1. 12 would give you an overall square footage of 1,290 square feet (120 m2). [6] X Research source
Always order 10% more materials than you think you need to account for waste, and round up to make sure you don’t come up short. In the above example, you’d need 15 squares.
Bring a tape measure, pen or pencil, and notebook or pad of paper with you. You’ll need these items to record your roof’s measurements. Make sure your ladder is resting on a flat, stable patch of ground. If possible, have a helper hold it for you to stabilize it as you climb. [9] X Research source
Complete one side at a time before moving on to other areas. You’re just looking for the outer perimeter at this stage. In this context, a “plane” is defined as each flat, continuous section of the roof. [12] X Research source
Ridges and valleys are the top and bottom contours where smaller hip sections join the main part of the roof. Dormers are separate protruding structures that house windows in the upper floors of the house. They’re ordinarily roofed separately. [15] X Research source There’s no need to account for chimneys, pipes, or other irregularities. You or your roofing contractor will work around these areas once the project is actually underway.
Don’t round your roof measurements up or down. This will be done once it’s time to determine the number of shingles you need. Rounding before you begin multiplying and adding may throw off the accuracy of your final estimate.
Your diagram doesn’t need to be perfect. All that matters is that you have a visual aid to keep up with the various dimensions you’ll be using to make your final calculations. Use a pencil rather than a pen. That way, you’ll be able to make corrections and revisions as needed while you work.
The idea is to reduce your roof to a series of lines in order to simplify your subsequent calculations.
Keep lining off the different parts of your roof until each section is a square, rectangle, or triangle. Breaking your diagram up into smaller sections may seem unnecessarily complicated, but it will actually make your final calculations much faster and easier (unless you want to figure out how to find the area of a trapezoid).
If a section is 120 feet (37 m) x 100 feet (30 m), its total square footage would be 12,000 square feet (1,100 m2). Be sure to find the area of any dormers on your roof, as well.
The basic formula for finding the area of a triangle is ½ the base times the height (in this case, the distance between the base and the peak). If you have a roof section that’s 30 feet (9. 1 m) long and 12 feet (3. 7 m) high, multiplying those dimensions would give you an area of 180 square feet (17 m2). [21] X Research source Measure and mark the square footage of each triangular section carefully, as these tend to differ in size.
Together, two 750 sq ft (70 m2) rectangular planes and four 135 sq ft (12. 5 m2) triangular planes would give you a total area of 2,040 square feet (190 m2). Add up the numbers a few times to ensure that the final figure you get is correct. Take your time and work carefully to prevent mistakes. Even a small miscalculation could end up costing you time or money.
For a 12,000 sq ft (1,100 m2) roof, you’ll need a minimum of 120 squares. It’s a good idea to add an extra 10% to your estimated material requirements to account for waste and ensure that you have enough shingles to cover your roof when it’s all said and done. Using the above example, that would be 132 squares.
