Reducing the "minimum frost" depth 2

[TBell47]

Might anyone have suggestions or information regarding an acceptable method of reducing the "minimum frost depth" (in this case ~ 42") utilizing light weight concrete or foam insulation?
Can either of these materials be used in an acceptable manner to achieve this goal? Might there be other methods available that I'm not aware of?

Thank you!
Thomas

 

[CarlB]

Yes, insulating foundations is a proven method of reducing frost effects on foundations, allowing a shallower design. See "frost protected shallow foundation design" at

http://www.huduser.org/publications/destech/desguide.html.

For example the maximum frost depth in Anchorage, Alaska is about 10 feet, but the standard foundation for a heated building has 42 inches of cover, plus 2" subgrade insulation attached to the foundation wall. Even shallower foundations are allowed with additional (usually horizontal) insulation.

 

[dirtguy4]

CarlB,

Very nicely done.

 

[jike]

I agree with the recommendation of an insulated foundation. The amount of insulation will vary depending upon whether it is a heated or unheated structure, air freeze index and the mean annual temperature for the project location.

You might want to also consider replacing the existing soil with a non-frost suceptible fill material down to the frost depth. The non-frost suceptible fill material actually will freeze faster but will not heave. A non-frost suceptible fill material is defined as one having a very low percentage (say 5% or less) of fine material (passing a no. 200 sieve). This material will reduce the formation of ice lenses since the water can not be transmitted thru the soil particles by capillary action. It is also advisable to keep the soil drained.

Another option is to build a self-supporting structure (with an adequate gap beneath) and support it on frost depth foundations.