Building below the frost line: Why?

SkyWatcher

Been doing some research on foundations. One of the important things that has to be done is to dig below and pour the foundation footings below the frost line. It seems that this is especially important with pier type foundations.

Okay 3 questions. How do you find out where the frost line is at? How far below the frost line do you dig and pour? And why do you have to do this in the first place?

I'd appreciate input from anybody with any relevant experience. I've been finding out that there is not a ton of information available online in regard to foundations (especially pier foundations).

To whom much is given, much is expected.

Travis Hallam

It is my understanding that you have to go below the frost line due to the frost thawing and unthawing will cause your foundation to shift and become uneven. Going below the frostline will prevent this. Your frost line varies depending on your area of the country and the severity of your winters. I would guess at least one foot below the frost line for a minimum.

Mad Dog

Rickstir

Your county building department can tell you where the frost line is in your area. The farther north you go the deeper it gets. The reason you do this is to keep freeze/thaw cycles from "heaving" your pier or foundation. Just make sure the top of the "footing" is below frost line and you should be okay. Although the frost line is 36 inches in MO. I have had on two occasions to limit piers to 24 inches and have not had a problem. One of these installations is the pier for a deck that has 3 of the 4 piers in water, and I have not had a problem. My wife calls it the fishing deck, I call it the beer deck [:D]


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dakotashooter2

Travis and Rick have put you on the right track. A reputable contractor or the county soil conservation office in your area would also be able to tell you what the frost depth is. In your area I can't imagine it is very deep. Here in ND it can run 4'-6' depending on location and average temp& snow cover.

nord

The simplest answer is a question... Ever notice that a farmer harvests stones from his fields in the spring? This is a result of frost action (among other things).

Get a puddle of water below your footer and let it freeze, then expect the wall to heave and crack. Here we're supposed to be 32" below level. We plan footers for 48" as added insurance.

You can "float" a pad on a gravel bed, but it's going to crack and move anywhere there's freezing and the soil is less than perfectly drained.

And now you know.

Nord

SkyWatcher

That makes sense. I guess I was thinking of freezing water moving parts of the foundation in the horizontal plane, and completely disregarding the fact that freezing water can just as likely move a footing/pier vertically. Thanks for the info.

To whom much is given, much is expected.

woodsrunner

Make sure you get below the frost line! There is a woodshed addition on the back of my house, that I have to jack up every year and straighten the piers under. Hopefully this summer I'll stop being so cheap and get 3 sonotubes and fix the probelm. I haven't done it yet because I've wanted to tear it down and build a sunroom there. Now that I've decided to move I'm just going to fix it.

Woods

gruntled

This might explain why they still build basements some places & there are none here in So. Kalifornia.
If you have to dig a foundation down that deep you might as well use it.

jsergovic

You'all want the foundation where the soil temp is constant, usually about 57F.

The frost line is how deep the ground temp changes due to atmospheric conditions.

Similarly, you might know wekk water stays a constant temp. year around. Same reason.

jjmitchell60

Here in KY you are looking at a 30 inch frost line level for our harshest winter. same with water pipes, yopu want to have them below freeze line as well.

"we are but men... no more, no less..."

pabooger

Here in Pa the frost line is 36 inches!!! When pouring piers I always hollow out the hole at the bottom a little so that the bottom of the hole is wider than the top! This helps prevent the pier from heaving if the frost gets that deep!
Up here all water lines and footers are put at least 3 feet deep!



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RugerNiner

Also your Water Pipe and Sewer Pipe has to be below the Frost line.
You want the Water Pipe to come through the Block.
36" Lancaster, PA.


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bambihunter

quote:Originally posted by gruntled
This might explain why they still build basements some places & there are none here in So. Kalifornia.
If you have to dig a foundation down that deep you might as well use it.


Sometimes basements aren't done because of the soil around them won't drain properly. They have a saying here in Oklahoma with all our clay dirt "there's two types of basements, ones that leak and ones that WILL leak".