Cob: Good Foundations

[puppetman at ix.netcom.com]

The more I read about building construction the more I get conflicting information. 

In the building code of South Lyon (small city) Michigan,USA they state that foundations should be a minimum of 48" deep. Unless the building is less than 400sq ft. then it must only be 28" deep.

Can anyone explain the rational behind this? If the purpose of a deep foundation is to get below the 41" frost line, then how will 28" be adequate? Do they figure 400 sq ft is not a permanent building? Or have they found that a 28" foundation will support a small building just fine?

I have been reading some on rubble foundations and have found that they rely on insulation and heat from the building as well as drainage. I am building in an old, very flat, cornfield. the most drainage I could get would be two feet. Does berming work to prevent frost heave? If I could drain a rubble trench two feet below grade and then berm to two feet above grade say out to 8 ft from the walls, would that raise the frost line sufficiently to prevent heave? 

I am about to order my cinva-ram and I am still a little nervous about using earth blocks below grade. Will concrete stabilize an earthblock enough to keep it from degrading underground?

So many questions, so little time.

Thanx
Michael Fitzgerald
Anthropologist/Woodcarver/Puppetmaker