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Old 05-03-2012, 03:22 PM
Mike LI Male Mike LI is offline
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Join Date: Feb 2011
Posts: 397
Default Frost line question

So I have to be below the frost line. The frost line is 4 feet. I want to elevate 2 feet, does this mean I have to go down 8 feet? Something doesn't seem right. Anyone have any experience with this type of situation?

Thanks in advance

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Old 05-03-2012, 03:36 PM
grumble Male grumble is offline
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Join Date: Oct 2010
Location: W NM, a rifle shot from the Great Divide
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What is it you're burying? If it's a water tank, you need the base of the tank to be at least a foot below the freeze level, two feet is better. The whole tank doesn't have to be that deep, only the base of it. Convection and circulation inside the tank will prevent it from freezing.
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Old 05-04-2012, 06:56 PM
Plowpoint Male Plowpoint is offline
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Join Date: Feb 2012
Location: Maine
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You can greatly lower the depth by using foam insulation. Here in Maine, if you toss down a 2" piece of foam board on the ground, frost will not go underneath it. By burying foam on top of whatever it is you are trying to keep from freezing/moving with frost action, you can greatly reduce the burial depth.

For instance in my house I put 2" Styrofoam over the pipe going from my well into my house because I could not bury it as deeply as I wanted too. Even with a driveway going right over it (no snow cover to limit frost depth) it has never froze in the past 17 years. (Note minus sign in front of picture of outside temp making this statement impressive).

Styrofoam is expensive, but it can be cost effective depending upon what your project is.
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Old 05-08-2012, 10:16 AM
Mike LI Male Mike LI is offline
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Join Date: Feb 2011
Posts: 397

Building the cabin on pier posts. So it's a 4 foot frost line now that means I have to get below that correct? S0 they want like 18 inches of concrete which is gonna be a bear because I'm gonna hit water at about 4 feet maybe 6 since I'm building on the higher ground. Gotta set gravel in then pour then set the pier. Least thats what it looks like on the drawings.

Here's another question just for arguments sake lets say I run my piers north to south, how do I join them east west, with the joists?

BTW the styrofoam is brilliant, I wonder if I could use it as a cover or a form box.
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Old 05-11-2012, 07:00 PM
offtheradar Male offtheradar is offline
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Join Date: Mar 2012
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I'm not sure that I am following you. You are building a cabin with piers that set on a footer and the footer has to have four feet of cover due to the frost line. The footer is 18 inches thick so the invert of the footer is five and a half feet below the ground. The ground water level is four feet. If this is the case then you are going to have to dig a sump hole beside the footer forms and run a sump pump while working in the footer also when pouring the concrete. This is not cheap or easy but I have done this and it works. You could also drive the piers to the depth plus for load bearing without footers.

Note: OSHA requires that any thing over three feet in depth needs shoring or cut back.
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