Hi everyone,
I am getting ready to build a 10x14 or 12x18 little house next month on my land in eastern Tennessee. This is my first major building project. My proposed building site is sloped with excellent drainage; however, the soil is more than likely high in clay content. I'll be out there in a couple weeks to do some soil testing and more accurately assess the soil conditions, but I'm almost certain that the soil is predominately clay. My initial thinking is to fill the footing holes beneath the pier blocks with crushed rock and gravel, and then dig a French drain around the perimeter of the cabin. Will this be sufficient to prevent frost heave problems with the clay soil, or will I have to pour concrete down to the frost line?
In expansive clay I wouldn't advise that you do the Little House type shallow post and pier foundation. And a sloped site just adds extra problems with bracing and potential differential movement. A french drain will help dry out the soil but may not eliminate frost heave. It is more expensive, but you would likely be better off doing a perimeter stem wall foundation with footings and drains at the local frost depth.
You can try a simple test of your soil by filling a quart jar with the soil at footing depth, fully saturating it with water and then putting it in the freezer. Does it expand as it freezes?
You can also ask around for what kinds of foundation issues people have had to deal with in similar soils.
Thanks John. I'll do the jar test and see what happens!