Deck post depth in solid rock conditions

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Posted by: from Kanata
4/28/2016 at 5:34:48 PM

I am building a 12ft x 16ft deck in my back yard. My basement is only 44" below grade because the house is built (1994) on top of a large slab of granite in Kanata Ontario. The deck floor is 67" from the ground. The City of Ottawa wants me to dig a 5ft hole for each of my 6 foundation posts. To go down 5 feet I would have to drill through 1.5ft of solid rock in each hole.

I believe a better solution is to put the foundation posts on post blocks since the deck is not attached to the house. Or do you have a better solution?

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Date/Time4/28/2016 at 6:31:35 PM

Hi there,

If you can dig to the rock,should be able to drill 4 holes for rebar and expoxy the rebar in place place, make a cage with rebar then place sonotube over the rebar and pour them full of concrete and put you deck post plates in the concrete, check with your building inspector, or consult an engineer.

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Date/Time4/28/2016 at 7:56:35 PM

If your deck is not attached to your home and your not building a gazebo or any structure on the deck it is completely fine to construct your deck on deck blocks.

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Date/Time4/28/2016 at 9:41:59 PM


If you drill until you hit the slab that the home build hit. Just pour your concrete around the posts for the deck to that level. You have to get to a level that will prohibit movement with the freeze thaw of the seasons. And I assume the whole slab your home is built on is not going up and down winter to summer. Just make that clear to the building dept.

Enjoy the deck.

By the way in Southern Ontario we just go down 4'.

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Date/Time5/1/2016 at 9:16:45 AM

I would talk to the city about drilling into the rock, adding a steel pin, and then poring concrete inside a 12 inch sona tube to grade and add a galvanized bracket.

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