Plans typically show horizontal and vertical dimensions and the slope of the roof. This roof is 1,820 square feet on the flat, but to estimate sheathing and roofing materials it's necessary to determine the area on the slope. First, using the Pythagorean theorem, calculate the slope distance — 13.4164 inches per foot of run for a 6/12 roof. The ratio between this slope distance and a unit of run is called the pitch factor. Multiplying the run of the roof by the pitch factor gives the slope, or rake, distance of that roof. Multiplying the area of the roof on the flat by the pitch factor gives the sloped area of the roof.
Plans typically show horizontal and vertical dimensions and the slope of the roof. This roof is 1,820 square feet on the flat, but to estimate sheathing and roofing materials it's necessary to determine the area on the slope. First, using the Pythagorean theorem, calculate the slope distance — 13.4164 inches per foot of run for a 6/12 roof. The ratio between this slope distance and a unit of run is called the pitch factor. Multiplying the run of the roof by the pitch factor gives the slope, or rake, distance of that roof. Multiplying the area of the roof on the flat by the pitch factor gives the sloped area of the roof.

In my past job as an estimator for a lumberyard, I did hundreds of material takeoffs every year, and I still do them in my current job as an architectural draftsman. Some estimators use specialized software, but I estimate the same way many contractors do — with a spreadsheet. Almost any spreadsheet will do; I happen to use Excel.

You can create a spreadsheet estimating template without knowing more than a few basic functions — how to add, subtract, multiply, and divide. But it's worth taking the time to learn a few more advanced functions: Not only will you be able to use them in your estimating spreadsheet, but you'll be able to create spreadsheets for many other...

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