Cob: Pier system in Clay soil

[Darel Henman]

Sarah,
  the soil wont expand when frozen unless its wet I believe.  In this
case, you might want to consider putting an insulative water barrier
under the first two feet or so, to keep that at deeper depths from
getting wet.  Just a side issue thought for you.  You could start it
around a cob buildings base or a few fee up on the wall.  Eventually, in
a year or two, the frost line around the house will change to a shallow
area.

Darel

sarah kercheval wrote:
> 
> I need help with devoloping a peir system for a 28x28 foot log house with a
> cob addition.  We live in Minnesota which has 4-5 foot frost line, and
> really thick clay soil, which has a tendency to expand when frozen.  Had
> thought about French drains or rubble trench  system  but how do I integrate
> my peirs? How far do you need to go down in this climate for a rubble
> foundation?
> thanks
> Sarah
>