Foundation/Frost line

[xsscx]

I am building a new home. The home has decorative brick wing walls at each corner supported by concrete foundation walls. One of the walls was only poured 36" deep. The frost line in my area is 42" deep. Will I have a problem with frost heave? What can I do to extend the wall below the frost line? The foundation wall sits on very stiff to hard clay. Thank you

 

[SirAl]

Frost heave will depend upon the nature and condition of the subsoils, location of watertable or other potential free water source, and heating details of your house. You can protect shallow foundations inexpensively with rigid insulation. Refer to the following link for details:

http://www.dow.com/webapps/lit/litorder.asp?objid=09002f1380026990&filepath=/noreg

 

[eric1037]

If it's only a matter of 6" you could add additional soil at that location. 6 inches of topsoil for landscaping would probably be the easiest. You could also use gravel, concrete, brick pavers etc. as long as it ends up being 42 inches from the top to the bottom of the footing.

Insulation is only effective on the outside of the foundation. You need to keep frost from getting under the edge of the foundation. You could potentially use it, but I think it would be a waste of cash and it would be relatively time consuming.

 

[CarlB]

I agree with SirAl. Insulated foundations is a proven effective method in cold regions. It is the standard foundation design in Anchorage, Alaska, where the design frost depth in snow-free areas is about 10 feet. Anchorage code requires 42" cover over footings for heated buildings, with insulation typically vertical on the foundation wall. You can also place insulation horizontal, or a combination of horizontal and vertical. See SirAl's link to DOW styrofoam for placement.

 

[eric1037]

I would agree with using insulation, as long as it's used properly. That would include placing insulation along-side the foundation as well as horizontally in the vicinity of the foundation.

This would particularly applicable if it's not possible to raise grades 6 inches. However, if it's possible to raise grades, I think the use of soil would be more cost effective.

 

[georon]

Looking for estimated frost depth for building foundation on top of Wolf Creek Pass (el. 10,500). Reference books, software and/or maps that delineate subjsect depths would also be helpful.

 

[jjeng2]

If possible I would grade the exterior higher. You might not have a frost heave problem if you leave it as is. Have you had your building inspection yet? I dont know any inspector that would let that footing stay.