Hi Deborah BurianTake a look on a website called buildingscience dot comI'll try to link to an article...no affiliation, just a good reference site:http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriersI'd say if that wall doesn't have it, none of them do.

Hopefully the price included a vapor barrier and gravel?

As you don't have listed where you are - and you did not state what kind of foundation it is - we have no idea if it is a slab or a basement foundation, no idea how old the foundation is, what construction materials, what construction quality, completely in-ground versus walk-out (if not a slab), what was the cause of the explosion, how bad was the explosion (did it vaporize the house or just start a fire that necessitated razing the house... and on, and on....Even if the county approves re-using the existing foundation, I would not rely on the county inspector - after all, they just inspect things to code - the DO NOT inspect things as would a structural engineer.

Install vapor barrier, fans, or drainage pipes to remedy it.

There is a large cover or sheet under the home, which is probably some sort of vapor barrier.

The next step in the slab process is installing the post-tension cables and vapor barrier.

The cause was not determined.It is recommended to make modifications to the attic ventilation system in this home in order to meet minimum requirements -inadequate soffit venting.The inspection has identified an active plumbing leak at joint within water supply piping under home as seen in crawl area.The access opening size (for small crawl area) is not adequate to allow for easy entrance to the crawl area.The vapor barrier/plastic covering on floor of crawl area needs repair to provide the intended service.

Assuming it is all concrete, do I need a vapor barrier **AND** underlayment beneath a floating engineered hardwood floor?

Toss all incandescent, fluorescent, halogen, mercury vapor, etc.

Properly installing a vapor barrier is critical if you have a crawl space.