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Estimating the amount of material you will need to build a deck is part art, part science. You may not hit the quantities exactly right, but you can get close with the formulas and methods on this page. It’s also wise to check the return policy of your supplier beforehand; make sure you can bring back any unused salable items for a full refund.
For a small deck (10 × 12 feet, for example), determine how much lumber you’ll need by using your detailed plans to count all the pieces of each size—12-foot 2 × 4s, 8-foot 2 × 6s, and so on—for all framing members, including stairs and railings. Add 10 percent to framing and 15 percent to decking to allow for waste.
Calculate the decking required based on the actual width of the boards you will use, including the gap between boards. The ends of stock decking lengths won’t always fall exactly on joists spaced on 16-inch centers. Figure the lengths necessary to fit the joist spacing with minimum waste. (Add an extra 15 percent for diagonal decking.)
For larger decks, you can calculate the total square footage of decking you need by multiplying the length of the deck surface times the width. Allow for overhangs. Then buy enough lineal feet of decking to make up the deck area plus the waste allowance. Make actual counts of posts, beams, joists, and other framing members.
For Round Footings:
For Rectangular Pads and Footings:
Count the number of metal connectors and fasteners necessary for the framing (see Framing section). Estimate 5 pounds of screws (or nails) for every 100 square feet of decking.
Computing Stair and Railing Dimensions
Before you place your material order, determine how much lumber you’ll need for stairs and railings. Refer to your drawings to determine the number of posts, balusters, rails, stair treads and stringers. Because actual on-site dimensions can vary from drawings and estimates, be sure to take actual on-site measurements before constructing stairs or railings.
|WORK SMARTER: Length of Lumber
Lengths of lumber come in even 2-foot intervals. Most stock is slightly longer than stated—a 12-foot board may measure 144¼ inches, for example. If you will cut several lengths from a board, allow for the saw's kerf (the empty space cut out by the blade) when estimating.
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