Deck Building Don’ts
People tend to think of decks as simple projects that don’t require much skill or oversight. Judging from the number of deck collapses I read about and the number of unsafe decks I’ve seen, people are wrong. Below is a short list of things not to do. There are many others, but these are my personal pet peeves.
- Don’t skip the permit. Yeah, the deck is at the back of the house, and you probably won’t get caught. But permits don’t cost much, they help to ensure that the deck is built safely, and you will get caught eventually. That might only happen when you sell the house, but who needs that entirely avoidable headache at an otherwise stressful time?
- Don’t skip the bolts. The most common cause of deck collapses is probably unbolted or inadequately bolted ledgers. This connection has to transfer thousands of pounds of load to the house. Nails alone don’t do it. Use 1/2-in. lag bolts, either hot-dipped galvanized or stainless steel, and long enough to poke through the back side of the band joist, or use proprietary structural screws. Observe the fastening schedule in the code or as provided by the fastener manufacturer.
- Don’t skip the flashing. The second-most common cause of deck collapses is probably when the builder doesn’t flash the house wall to keep water from getting behind the ledger. While the pressure-treated ledger isn’t likely to rot, the house framing isn’t so lucky. No matter how well you’ve bolted the ledger, when the material you’ve bolted it to rots, that deck is coming down.
- Don’t skip the hardware. I’ve seen several recent deck collapses that happened when the joists detached from the ledger because no joist hangers were used. Really? Joist hangers have been around as long as decks have. How is it possible that anyone isn’t using them?
- Don’t attach to a cantilever. Every so often I see a deck collapse because its ledger was attached to the band joist of a cantilevered floor. No amount of bolting or flashing will prevent a collapse in this case. The entire load of the ledger is placed on the nails holding that band joist to the end grain of the house joists. If you have a cantilever, either build a freestanding deck or run the deck joists through the cantilever so they bear on the house wall or foundation.
- Don’t attach to masonry veneer. Masonry veneer is siding, not a structural assembly. It is not intended to support a load. Using long lags to attach to the framing behind the brick isn’t a work-around either, because the bending force imposed on the bolts is too great. Build a freestanding deck instead.
- Don’t skip the end-cut preservative. Sometimes I think I’m the only person who’s ever heard of this stuff (I use Wolman Copper-Coat), but the code specifically requires its use on end cuts. Pressure treatment doesn’t always reach the center of a board, and cutting can expose untreated wood to decay organisms.
- Don’t use 2x10s for stair stringers. When notching a dimensional lumber stringer, code requires leaving at least 5 in. of lumber below the deepest point of the notch. That doesn’t happen when you notch 2×10 stringers for a stair with a code-compliant rise and run. Even so, many of the notched stringers sold in home centers are made from 2x10s. Don’t use them. Use solid stringers, or notch 2x12s. When using notched stringers, support them on posts and footings at least every 6 ft.
- Don’t add a hot tub without proper design. What’s better than relaxing in a hot tub with a cold beer? Not much, except also knowing that the tub isn’t going to fall through the deck. Hot tubs impose a point load that’s measurable in tons. Never add one to a deck that hasn’t been specifically designed for the load.
- Don’t put dissimilar metals in contact with each other. If you use galvanized hardware, fasten it with galvanized nails or structural screws. If you use stainless-steel hardware, fasten it with stainless-steel nails or structural screws. I’ve heard of one case where stainless-steel nails were used with galvanized joist hangers. The nails were fine. The hangers rusted out around them within a couple of years.
- Don’t install decking without spacing it. Tight joints between deck boards trap debris and water. That can start rot in the joists, particularly west of the Rockies where the Douglas fir or hemlock dimensional lumber used outdoors doesn’t take pressure treatment as well as the southern pine used in the East.