Frost depth

[recentgrad]

Footing should be below frost depth? and why?

 

[JStephen]

Water expands when it freezes. Freezing water under the foundation will raise it up a tad. And a bit more everytime it freezes after that.

 

[BigH]

A bit more complicated than that - but, recentgrad, why don't you review your university soils book or get any of a number of very good ones (e.g., Terzaghi, Peck and Mesri). I have put footing above the frost penetration level on a number of locations because (1) the soil was non-frost susceptible and (2) the groundwater was well down. For frost heave you need (a) water and (b) frost susceptible medium.

 

[dicksewerrat]

Also because the inspector says so.

 

[amorrison]

Its nice to know good google search words.

Like NRC Canada frost footing*

Try

http://irc.nrc-cnrc.gc.ca/cbd/cbd182e.html

http://irc.nrc-cnrc.gc.ca/cbd/cbd128e.html

 

[Grizzman]

In the southeast, the frost line is generally regarded as finish grade.

 

[BFPartners]

Up here, frost goes down to 8 ft in ditches/fields and up to 11.5 ft under roads. Frost suseptable soils are not solid enough due to water expansion and soil movement which can cause structural damage. Most soils experience somesort of soil freeze/thaw action in the spring time due to warm days and freezing nights!