Regarding the influence of soil type, i'll put some info of my own.
Brett is right when he says that soil type has a large influence on foundation type.
Most problems (but not all) come from
water.
If there's a sandy soil that drain fast, you don't need to care much about the water problem as there's not a lot of clay and the excess water will just drain away.
Of course you have to care about the sand being structural but that's a different problem.
But if you have clay or heavy clay, things are different.
Even if you go below frost line, clay will swell a lot if water gets to it.
If you have a gravel trench / stone foundation, water will flow thru to the bottom clay and cause problems.
In this scenario you need the ditch or the entire
footprint set at an angle to drain any water to a lower spot.
If you're on a hill, it's simple, but if you're on flat
land and if maybe water tables are high ... you have problems.
That's why
concrete has a lot of appeal for modern homo impatiens.
People don't have to think and leave out the attention to details.
Basically, concrete is a soil replacement that's not sensitive to seasonal change.
Since it replaces the excavated soil, water can't (usually) get easily underneath to cause havoc.
But if you have a rubble trench, that's exactly what's going to happen.
PS
Loved the
wood building replica on the shake table.
I wish more people in the "norming" business would care ...
