Cottage Q&A: Building a deck on rock

We would like to build a deck that would be on top of rock that has concrete poured onto it. It’s a fairly flat surface, but can we moor the wooden deck to it somehow without having to use drilling equipment?—Lynn Beninger, via email

Probably not if you want to a) build a safe deck; and b) follow the building code.

“Concrete won’t adhere to bedrock on its own,” says Greg Potticary with Hickory Dickory Decks in Dundas, Ont. “It’s imperative that you drill into the rock to properly adhere the deck’s footings.”

“Fairly flat” isn’t the same as pancake flat. “If there’s any grade at all, you’ll get slippage,” says Cottage Life’s project builder, Wayne Lennox. And, for reasons that we assume are obvious, slippage is not good. “Besides, there’s nothing pretty about some bare Sonotube extending up from a rock face,” says Lennox.

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If you’re building on rock, the general procedure is to make level concrete forms anchored to the rock with rebar and epoxy. Lennox—who has built several decks on rock—would then use saddle rebar brackets to securely hold the deck’s posts. The size of the concrete forms, and the number and depth of the drilled holes and rebar, will depend on your local building department’s requirements. “I love building on rock,” says Lennox. “I actually think it’s so much easier than building on soil.”

That’s cool for him, but it sounds like you feel differently. Since building regulations can vary, it’s worth finding out if there’s some workaround that can still legally get you the drilling-free deck of your dreams. Example? While, as described, your project wouldn’t meet the “anchorage and frost depth sections” of the building code, Marty Herbert, with the building and bylaw services department of B.C.’s Columbia Shuswap Regional District, says it might be possible if it were designed by a registered professional engineer. Consult your local building inspector, and go from there.

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This article was originally published in the October 2020 issue of Cottage Life magazine.

Got a question for Cottage Q&A? Send it to answers@cottagelife.com.

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