- High-end residential builder here
Some other homes on the hill had to be built on pilings because they were in an area which was loose dirt that had eroded away from higher up.
I'm not sure if 'clay' is the right word, I don't know much about geology, but the geologist definitely said compacted "glacial till" which he said was ideal.
Haven't had any settling problems so far despite an earthquake and lots of rain.
I passed on another lot where the geologist said the whole hill was going to slide away at some point. The seller didn't want to hear that.
The kind of glacial packed clay mentioned in this article is the sort of stuff even a power shovel has trouble with. It looks like light coloured slate, dry, brittle, and dense.
I'm not sure what your preference for sand is other than it's easy to work with. That stuff can shift, it bloats when wet and heaves with frost, settles like crazy under pressure. Sure, it's easy to remove, but it's so variable I have no idea how you'd get anything to stay level on top of it.
I wonder what kind of foundation these homes are built on. Do they include a full basement?
Living somewhere built on what is apparently some of the most variable types of clay and that experiences temperature swings of ~150F throughout the year: we don't.
Any basement more than 30 years old is cracked and heaved. Houses require constant adjustment of the teleposts to avoid large cracks forming in the house built on top of the foundation.