If your slab foundation is built like the one in our San Antonio house, there are large wide channels with rebar that are built like a grid around the house perimeter and under the house, and these serve as footings and cross beams. You need packed or undisturbed soil under those areas because they are footings. Local code should require inspection of the soil under the footings to ensure it is undisturbed.

However, between these "beam" areas there is a lot of fill under the rest of the cement floor. I think it would be best if it was packed, but since that fill only supports the slab (5"-6" thick), and does not support the house framing, you may be able to get by with loose dirt in those areas. In our house it was also bagged with large sheets of plastic.

Bruce

Bruce

The terms you want are "tract" and "compact", The need for compaction depends on whether or not the slab is supported by the fill or its structural (spans between supports). It also depends on the kind of fill. Its possible that compaction is not necessary but its easier for you to tell us what the actual conditions are rather than for us to explain all the condition where compaction is not needed.

For this location the foundation might be post-tensioned.

Is it an engineered slab? I don't know if that makes a difference. I remember when we bought a house south of Houstonwith potential cracked slab. Everyone said no big deal, in Houston it's not a matter of if your slab is cracked, but when it will crack. Got to love gumbo clay.

We've got clay in my part of Texas, too (Central), and most houses are built on slabs. Cracked slabs are normal.

But just because something is normal doesn't mean it's smart. One of the ways I vetted architects was asking if they used other methods of foundation construction. One said he sent foundations to his engineer who did slabs only. I didn't select him (there were other reasons, but that was a big one).

I'm currently in a tract home, with a slab foundation. I expect it to crack, because our soil moves so much. We have thick, heavy, black clay everywhere, and my foundation is nearly 3' tall/thick in a back corner. The upside is, when I go to sell, almost all other houses have the same problem, so realtors/buyers won't consider it an issue.

If you have concerns, contact a geotechnical (soils) engineer for testing of the soil. That assumes the contractor that owns the site will agree. If not...

Apparently he got an answer.

3 month old post

Amazing how often this term is used...