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The frost line is 1.2m deep in my area. That seems like a lot of concrete to pour for a fence post.

I'm wondering if a better way is to make a shorter footer following the suggestion that's used in wooden posts shown below, but with concrete footers:

Diagram showing conical-shaped wooden fence posts

Digging a hole like this seems tricky, so a concrete form seems like a better way. I found a patent for this kind of forms, but don't know where they can be purchased.

So, my questions:

  • Would a shallower conical post resolve the issue of frost heaving?
  • If so, how shallow? Wind load is a factor, so assuming a 2m high privacy fence, perhaps all of this is moot.
  • Where can one buy conical forms?
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1 Answer 1

You can't escape physics and violate code, which places footing depths below frost depths. Just be glad you're not in Alberta, I hear they must go to 12ft.

Where restraint in the form of a building load is present, heaving pressures may or may not overcome the restraint, but they can be very high: 19 tons/sq ft has been measured, and a seven-story reinforced concrete frame building on a raft foundation was observed to heave more than 2 in

Concrete Network article on shallow footings and frost

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This Concrete Network article is interesting. The more I read about frost-heaving, the more I get the impression that the diagram has a flawed hypothesis. It seems that heaving occurs more because ice lenses grab and force the posts up as they grow (up). The growth is upward because of ground water being supplied from below. Still, this begs the question why going below the frost line solves the problem. that is, an ice lens can still form anywhere and heave the post. Perhaps it's more a question of total length (harder to heave) than the fact that it's below the frost line. –  Fuhrmanator Jun 13 '13 at 20:07

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