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Estimating Plywood for Roof Decking

One of the most time-consuming, yet important, tasks of any do-it-yourself project is estimating your materials needs. If you are pinching pennies, figuring your requirements precisely ensures you don't end up with a lot of wasted wood and other materials at the end of the job. Most construction materials in the U. S. come in standard sizes that work together efficiently, so that with basic math skills, a tape measure and a bit of common sense, this job need not be difficult.

Building or repairing a roof requires careful planning.

Step 1

Measure each plane of your roof to find the area in square feet.  Multiply the width times the length for each section. For example, a roof section that measures 30 feet by 50 feet would have an area of 1,500 square feet.  Write down all the numbers as you go so you don't lose track.

Step 2

Add together all the roof sections' measurements to get the total area you need to cover. 

Step 3

Divide the total roof area by 32 – the area of one sheet of 4-by-8-feet plywood.  The resulting number is the number of plywood sheets you need for one layer of decking on your roof. For example, 1,500 square feet divided by 32 square feet equals 46875 sheets.  Round to the nearest full sheet – in this case 47 – for the number to purchase.