5 ways to prevent deck collapse

Instead of going for a new deck altogether, try these steps to repair it first

By Ryan ShervillRyan Shervill


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Yes, you can build a smarter, safer deck from scratch, but what if you want the existing one a bit longer? If you have an older cottage, it’s likely the deck wasn’t built to current standards. Even many new decks need some TLC. Don’t ignore building errors: Catastrophic collapses—which can be deadly—do happen, often when there’s a crowd on board.

1. Nails aren’t enough

Nails just don’t hold the way screws do; supplement nail joints with stainless steel or coated screws (choose ones that can be used in pressure-treated wood). Balusters, railings, and support posts are all good candidates for reinforcement. It’s easy: No need to remove nails, simply reinforce the joint by driving #8 or #10 screws of the right length (at least twice the thickness of the piece you’re securing) wherever you find old nails. There’s one exception to the no-nails rule, mandated by the Ontario Building Code: Joist hangers must be affixed with joist-hanger nails, which have more shear resistance than screws.

2. Under, not beside

Is the deck’s main beam screwed or nailed to the face of a support post rather than set on top of it? It’s easier to build, but is an accident waiting to happen. The screws or nails used to face-attach support beams can’t be trusted to support a deck’s shear loads, and can pull away from the post over time. The best fix is to trim the post and replace the face-nailed beams with a new laminated beam, set on top of the post. A galvanized metal saddle bracket on the post will ease fastening and keep the assembly solid. This is ideal, but it’s not easy to do under an existing deck. Another option is to install two 1/2″ hot-dipped galvanized bolts, with nuts and washers, through each post-and-beam junction. The bolts have ample shear strength and can’t pull out of the post.

3. Reconcile your ledger

I often see ledger boards (the pieces that attach decks to the buildings) nailed or screwed in place. This isn’t up to Code, and for good reason: It’s just not strong enough. In fact, ledger failure is the number one cause of deck collapse. If yours is nailed or screwed, but in good shape otherwise, reinforce the attachment by drilling pairs of holes every 16″ completely through both the ledger board and the cottage’s rim-joist (or masonry foundation), and fastening the two solidly together with hot-dipped galvanized or stainless bolts, nuts, and washers.

4. On the level?

Support posts sitting on deck blocks rather than poured footings can be raised by freeze-thaw cycles, tilting your deck towards the cottage. Ideally, it should slant slightly the other way to prevent water pooling against the building and causing rot. If your deck is on blocks, use a long level to check the tilt after spring thaw. If your deck has heaved, trim the bottom of the support posts or dig your blocks in a bit deeper.

5. Know your limits

Some cottagers have placed portable hot tubs on their decks, probably not realizing how heavy they are. Even a small four-person model can add more than 3,500 lbs. across a small area, much more weight per square foot than the Code factors in. The likelihood of a portable hot tub causing a deck collapse keeps building inspectors up at night, which is why they advise hiring a structural engineer to design modifications to support the load. A better solution is to put your tub on a ground-level platform where it will be safe and solid.

This article was originally published on July 17, 2010

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