Roofing Calculations

Measuring

• For the most accurate measurements, get on the roof and use a tape measure to calculate the surface area you're covering with the new roofing. If your roof is flat and square or rectangular, simply measure the length and width. Sketch out each flat area of the roof, and label it for reference. Write in the length and width of each section on the corresponding side of the picture. Move around carefully to measure each surface individually.

Calculations

• Once you're back on solid ground, use the measurements to calculate the roofing area. Calculating the surface area gives you a guide for buying the roofing materials. Multiple the length and width of each section of the roof to find the area. Write the area of each section on the drawing so you have a record of the data. Add together the surface area for each part of the roof to determine the total area of the roof.

Roofing Material

• Roofing comes in squares, enough to cover 100 square feet of surface on your roof. Determine how many squares you need by dividing the total roofing area by 100. For example, for a roof with 2,500 square feet of surface, divide 2,500 by 100 to get 25 squares.

Extras

• Even with accurate measurements, you may need extra shingles to complete the job. If you have lots of peaks or different roof areas that protrude from the house, you will likely need to cut shingles to make them fit properly. This cutting produces waste and takes away from the amount of shingles available. Add 10 percent of the total roof area to account for the extra shingles. On a 2,500-square-foot roof, this would mean an additional 250 square feet of shingles. Keep a few extra shingles on hand in case you need to replace damaged shingles in the future.