5 Tips for Building Pressure-Treated Decks

These five pro-grade construction tips will help anyone working on a treated wood deck to build it even better.

1. Joists—If it's necessary to install or replace a joist, be sure to inspect the board for its crown. Dimensional lumber is rarely perfectly straight, and the "crown" is the board's natural curvature when looking down the board's narrowest edge. The crown will give the board a slight bowed or arc shape, and when used as a deck joist, it's important to orient the high mid-point of the arc at the top to prevent sagging in the deck surface.

Fasten the ends of deck joists to ledger boards, beams or rim joists, using metal hangers secured with code-approved nails or screws.

2. Flashing Tape—For the best long-term weather protection, cover the tops of joists and framing members with a self-adhering tape used as flashing. These butyl or asphalt tapes protect fastener holes from moisture by acting as a non-corrosive barrier between treated lumber and metal hardware.

3. Decking—Before installing the deck boards, inspect their ends for the tree's growth rings. In general, it's best to install the boards bark-side up to reduce cupping. However, some boards that are cut closer to the core of the tree have a straighter, tighter grain, and therefore less cupping.

4. Shrinkage—A common mistake is spacing treated deck boards when installing them. Treated decking usually contains moisture from the treatment plant which causes the wood to swell. As the wood cures, you can expect the boards to shrink. For this reason, it's best to install the deck boards tightly together and allow the spacing to occur naturally over time. If you provide spacing between the boards during installation, then once the deck cures and the wood contracts, the gaps will likely be too large.

5. Notches—Need to cut a notch around a post? First, measure and mark the cut-out on the board. Use a drill with a bit slightly larger than a jigsaw blade to drill pilot holes at the corners of the notch. Then use the jigsaw to cut out the notch. The pilot holes will allow room to make an easy 90-degree turn with the jigsaw blade. Remember to seal the inside of the notch (and any other cuts in the lumber) with a wood preservative.

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