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I live in Quebec and I read articles from CAA and Rona (Lowes in the rest of Canada) stating that the concrete pillars for building decks posts should be between 4 or 5 feet tall in ground below the frost line to avoid any issue. I am planning to do the number 2 Concrete Pillars Without Footings from this article install a deck foundation

Talking with a Home Depot girl who knows well her job told me that I don't need to be that depth but 2 feet in ground + 6 inches of gravel first using those yellow cardboard quikrete building forms, adding that the weight of the deck is enough to hold the posts there.

Let's say I am planning to isolate and avoid contact of the snow with the posts during the winter. Have you experienced any issue building a deck with 2 feet concrete pilars in ground + 6 inches of gravel below in Quebec instead from the 4 feet long concrete pillar? Any move or stability issues apart from the theory?

EDIT: I mentioned Quebec, but I want to specify I live in Montreal's south shore. This may change the idea that I could live in the North where snow and cold is stronger than in Montreal.

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    I would ask a local contractor for a bid, to see what he says, and dont tell him about your plan
    – Traveler
    Jun 20, 2022 at 4:26
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    Point of order— it’s mostly Rona in the rest of Canada. There’s like one Lowes in my entire metro area and six Rona. Jun 20, 2022 at 5:51
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    When putting something in the ground that is not below the frost line, people are usually not happy inside of a few years. Have put in fence posts not far enough and the next year they would be raise up by about a foot. Dig down or use a floating system.
    – crip659
    Jun 20, 2022 at 10:09
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    It is usually much cheaper to pay and do it right the first time, than to keep redoing it. Usually it costs more to prepare to dig a hole than the digging itself, if doing it by a machine.
    – crip659
    Jun 20, 2022 at 12:54
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    Can usually get extensions to augers/post hole diggers.
    – crip659
    Jun 20, 2022 at 13:29

2 Answers 2

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The woman working at the hardware store is absolutely not qualified to give construction advice; she didn't even ask you any questions whatsoever about your deck.

You must go below the frost line when any of the following are true (I'm sure there are more than this, but I digress):

  • The deck is not a stand-alone unit (ie. it's attached to a building (eg. house)
  • The deck is more than 55 metres square
  • The deck has a roof
  • The deck is more than 30" from ground to the top of the walking surface at any point

The ground doesn't care what the weight of the deck is. Frost can and will shift your posts if not below the frost line.

Despite any rules, just rent a hole auger, spend a bit more on concrete, and do the job properly.

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  • Thank you for the answer I rented a 8in diameter auger machine for one since it is just me. It was so hard to do it but myself and I could dig 4 holes. One at 4 ft 3 in and the other three at 3 ft and 1 in. Ground was so compacted and machine couldn't go deeper than this I struggled so much doing this, in fact, the machine stopped drilling. Frost line is 4 ft according to QC rules and I should do it at 5 or 6 . I proceeded with the 6 inches of gravel and built my concrete pillars. My deck is 20 ft wide and 13 ft long. I will test it on winter. I am scared as hell. Jul 8, 2022 at 10:34
  • You should have gotten help to do it properly. You wouldn't have to sit and worry all year.
    – stevieb
    Jul 8, 2022 at 13:56
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Generally in Quebec the frost line is 5 feet. 2 feet is insufficient.

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  • wow, the OP knows that, how does it help him
    – Traveler
    Jun 20, 2022 at 7:13
  • I think the answer has all the relevant information: ** 2 feet is insufficient. ** I’m also guessing that the Home Depot staffer doesn’t have a contractor’s license or PEng designation. Jun 21, 2022 at 0:57

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