10 Tips for Choosing and Buying Deck Lumber
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Research Deck Boards Before You Buy
Each of the four main deck board categories has its advantages and disadvantages.
Natural softwoods
Cedar and redwood decking boards are beautiful, have fantastic grain and natural coloring and are very stable. They lay flat and won’t move, cup, crack or split as much as treated boards.
However, they will lose their color, fading to gray within about a year or two, says Kou, so they will require regular refurbishment with deck oil or other proprietary treatment. And while they aren’t the most expensive option, they aren’t the cheapest either.
Natural hardwoods
Exotic hardwoods, such as ipé, cumaru and teak, are grown on plantations in the tropics, so they aren’t as environmentally unfriendly as they seem, but they are undoubtedly the priciest option. Plus, they’ll outlast most other decking materials by many years and continue looking great with an occasional oil treatment.
Their main downside is that their density makes cutting boards and driving screws hard on your tools and a general pain.
Treated lumber
“Pressure-treated decking boards cost the least,” says Kou, “so if you plan on building a big deck, then they are probably the best choice. PT boards will also last longer than untreated cedar or redwood, but they will shrink, split, crack and warp if they have not been properly kiln-dried.”
Composite deck boards
Composite boards are marketed as rot and vermin-resistant, and while they’re made from recycled plastic and timber material, they aren’t necessarily recyclable themselves and usually end up in landfills when they wear out. “The boards will be consistent in color, texture, and finish, so will have a nice uniform appearance right across a deck,” says Kou.
On the downside, he says composite decking is usually priced higher than pressure-treated and natural softwood boards, and it doesn’t perform well in areas that experience extreme weather conditions (long periods of below-freezing temperatures, or over-exposure to sunlight.)
Moreover, composite boards are prone to sagging and bending, so they require more support than PT or natural wood boards. Kou recommends washing composite boards regularly because moss or algae build-up can make them slippery.
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Consider All Three Dimensions When Selecting Your Deck Boards
Some deck boards are thicker or wider and some have rounded edges. All perform a bit differently.
Width
“Be width-wise,” says Kou, who explains that even though four-inch boards are a little less expensive, stretching the budget to six inches will mean fewer cuts, fewer gaps, and fewer fasteners. “Don’t be tempted to use eight-inch,” he warns. “They will be more prone to splitting, cupping and crowning.”
Thickness
“Don’t skimp on thickness,” Kou continues. “Go for a minimum inch to inch-and-a-quarter thick boards. Anything less will require more joists to support it. Three-quarter-inch boards are too flimsy and will bend, even with 12-inch spacing on the deck joists.” If your joists are spaced at 24 inches, or you’re running your deck boards at a diagonal, you’ll probably need to use 2-by (1-1/2 in. thick) boards, which is a good default thickness.
Length
Purchase decking that can run the full length of your deck when possible. All lumberyards and home centers carry 16-ft. deck boards, but many also stock or can order 20- and 24-ft. boards, though they may cost more. “The advantage of working around supplied lengths will mean fewer cuts and fewer butt joints,” he says, and butt joints are potentially problematic. The ends of boards are more absorbent, slower to dry out and more susceptible to rotting, swelling and splintering. Fasteners driven close to the ends also tend to split the wood.
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Avoid “Scalped Edges” and Uneven Widths
When you’re purchasing boards, check the crown by sighting along the edge of the board, then check that crowned edge for scalped edges, called “wane.” Wane on the bottom of a joist is OK, but wane on the top means there’s less wood for driving fasteners into—and you can’t butt two deck boards on an uneven joist.
It’s actually preferable to use joists with a slight crown, “slight” being an upward bow of 1/4 to 1/2 inches. Joists settle and sag slightly as they support weight and movement, and a perfectly straight joist will wind up with a dip while one with a slight crown will end up being straight.
The joists’ widths (or depths) can vary by as much as 3/8 inches. The 12-ft. long 2x10s at your lumberyard may measure 9-1/8 in. in width, while the 16-footers measure 9-1/2 in. Deck boards secured to uneven joists will flex more, and the fasteners will creak and pop, so use joists that vary by less than an eighth of an inch.
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