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To calculate a corrugated metal roof, you must know the length and width of the roof onto which it will be installed.
Calculating a corrugated metal roof is as essential as the installation of the roof itself. Failure to correctly calculate the material amount can result in wasted material due to overestimating or lost time due to underestimating. The main objective in calculating corrugated metal roofing is understanding the coverage area of one sheet of metal. Thereafter, you can estimate amounts accurate to within one sheet of metal. The do-it-yourselfer can estimate a corrugated metal roofing project in two to four hours, depending on the size and scope of the project.
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Measure the length of the roof decking, including the overhangs. If you have a roof that is broken up into several sections, such as with a hip roof, then record the individual lengths onto a writing pad labeled "Section 1, Section 2" and so on. Keep these individual measurements separated.
Measure the width of the individual sections, including the overhang, and record them under the corresponding noted sections.
Multiply the length and width of each section to get the square footage of need and record that total under the same noted section. For example, if you have a section that is 10 feet long and 10 feet wide, then multiply the two to get 100 square feet.
Combine all square feet together to get a total square feet of corrugated metal roofing needed for the entire roofing job. Multiply that total times 5 percent — total amount of projected waste — to get a total amount of need plus waste. For example, if you have a total of 1,000 square feet of roof to cover, multiply that times .05 to get 50. Add 50 to 1,000 square feet, and you will need 1050 square feet of corrugated roofing material.
Determine the amount of coverage one sheet of corrugated sheet will cover. Call your metal provider and ask for the width of the corrugated metal, which is commonly 36 inches. Multiply the length of the sheet — sheets vary in length depending on your need — times the width. For example, 10 feet times 3 feet (36 inches wide) equals 30 square feet. One sheet will cover 30 square feet.
Divide the total square footage of need by the square feet of one sheet to get the number of 36-inch wide corrugated sheets needed to cover a roof of 1,050 square feet (1050/30=35). You will need 35 sheets of metal to cover your roof.