"according to GC the flooring sub-contractor was going to apply vapor barrier below the hardwood."

If that is in writing AND it wasn't done you might have recourse with GC who could choose to take action with floor sub. If architect speced vapor barrier and it wasn't installed you have recourse with GC. Most codes call for vapor barrier under slab,was that done? I don't believe you can do anything about it simply because no one warned you.

Anyone who specified or installed, or even thought about, putting solid on slab is completely and totally clueless. Shoulda been engineered all the way. You have a fundamental design error. Who specified solid wood anyway? Or was this one of your requests?

Hardwood over a concrete slab is a tough application. We have had good success installing glued-down engineered hardwood for such applications. The adhesive we use is waterproof and serves as the vapor barrier.

You indicated that the floor was cupped--not crowned--so the underside of the flooring is exposed to a higher moisture environment than the top surface. The problem is not with the humidity of the space above the flooring. Further, the fact that only a portion of the floor is affected suggests a localized moisture problem. I suggest you remove the flooring in that area and replace it with glued-down engineered product.

This doesn't change any thing but might answer the question of "why only one area"? If you alow a wide, thick board to lay in contact with ground during a few days of rain followed by warm sunny days,it will cup (edges raiseing toward sun). Reason? Wood swell's when wet then shrink's as it drys. Our test board dry's on skyward side while side next to ground continues pulling moisture from ground underneath. Flip it over and elevated off ground and you will notice cup diminishing over a few days. The damaged area of your floor recieve's radiant heat through door and window. The bad news is that in time remainder of floor will follow suit. Conclusion? Support's your initial suspicion floor is pulling moisture from concrete. Why? Only carful investigation can tell for certain. Even with proper moisture barriers in place I believe enough moisture can come from new concrete to cause damage. You will never intirely stop ALL moisture from migrating. The best we can hope for is slow it to the point it evaporate's as fast as it's drawn in from reverse side(a state of equilibrium/balance). If conditions are wet enough,bad things happen,even with barriers in place.

Concrete is a hard sponge. It wicks moisture, even with a vapor barrier under the slab. There are new very very expensive glues that combine a moisture barrier with an adhesive, but those are still problematic with solid wood, and only trustworthy with engineered.

In all cases, solid wood is always contra indicated below grade. All cases. It is simply a completely unsuitable material choice. Period. Even engineered isn't really gonna work for below grade. That is reserved for vinyl or carpet.

I believe everyone agree's wood floor was a poor choice,op's problem at this point is who's at fault. I reccomend assembling ever piece of related written info, jotting down your best recollection of converstaions,preserving text messages. Orginize everthing into a presentation and call a lawyer for a 1 hour consultation. 1 hour cost's from free to $300 depending on your choice of lawyers. If the GC handled everything from pouring slab to laying floor,he's at risk of being on the hook but you can expect him to fight.

Wood will rot when left in contact with damp concrete. That is all concrete. Even that with a vapor barrier underneath it. I have seen, and smelt, the results of the common practice around here of glueing down non marine grade plywood to the slab and then nailing solid flooring to that. It's not pretty, and it is a health hazard. And you won't know it until the wood starts to turn black from underneath. Solid wood won't have near the 15 year grace period of the plywood rotting out before it gets to the wood.

I would have major concerns about the other invisible portions of the remodel. This really is such a basic error.

Try to realize we have already gone farthur out on the ice than we should be without all the details. I'm not a floor pro so some of what I say is just opinion. If you are wanting people here to go into the much more I figure you will need to pull some floor to find some facts. I've never seen floor that couldn't have pieces removed and replaced. You need to figure how your floor type is done or hire somene that can.

Maybe you can call a local reputable flooring store to come out, pull up enough of the floor to let them see what's under there. You then have a documentable, knowledgeable witness. It won't harm the floor more than it already is, to just pull up a couple of boards. Although I'm no flooring expert, we have had professionals lay wood flooring, and I have read through just about every post possible on this website when we did that project. This is not really something that you should just "let go" because the cupping doesn't bother you too much aesthetically. Others are giving you good advice about the potential for mold, and the potential for further damage to the wood. Additionally, you need the evidence in order to force the contractor to either fix the issues or deal with lawyers. In this age of Yelp and the BBB, he ought to be very concerned about leaving each job professionally completed.

3. Exterior trim water table - I don't recall seeing any galvanized flashing over the water table,

The metal flashing should be easily detected since it extends over the water table trim. If its not there, ask the builder to correct his mistake.

4. Finished floor over concrete - Here there are specs on the barrier that should go below the hardwood - talks about spaces for expansion, plywood sheating, sleepers (which I just google to see what it is), polystrene, plus insulations, etc... - seems these are all to protect the floor from moisture

I don't see anything in this detail that would adequately protect the flooring from moisture. There is no waterproofing or vapor retarder membrane shown on top of the concrete where it belongs and it would be obvious in the detail since the membrane must turn up and be sealed at the perimeter. Styrofoam insulation could only act as a secondary vapor retarder since it is interrupted by the sleepers every 16" o.c.

The parenthetical note about sealing the "JOISTS" makes no sense; perhaps it was meant to say: "seal the JOINTS [of the insulation board] with tape or fiberglass mesh and mastic" creating a crude vapor retarder above the sleepers with adhesive joint seals that cover 20% of the floor area. This is not a vapor retarder like the ones used for exterior walls; its intended to stop moisture from the ground and it should be a thick membrane with no joints if at all possible and it should not be above wood sleepers. And why specify no insulation facing; were they afraid that a foil facing might act as a vapor retarder? You will need to open up part of the floor to see what was actually done.

Also, the wood sleepers are not specified to be pressure preservative treated which is a serious mistake and could be a code violation but an experienced sub or inspector would have corrected that design error.

In general, the details appear be poorly drawn and poorly noted. I doubt there was a design professional involved. Perhaps there is a specification that clarifies some of the cryptic and confusing notes.

But the fact that the damage is limited to one room is still puzzling. Perhaps there's more water under that part of the slab because of the walk out door and well.

May want to post this in flooring forum as well. There are pros over there that don't frequent this forum.

Would there be a reason why the room in question would have more humidity than the rest? You can get cupping if the humidity in the air above the floor is too high as well.

Otherwise, is the grade away from the house outside so water doesn't come towards the house? That could cause excess water near that room. Maybe a badly placed or clogged downspout?

The use of XPS with sleepers really minimizes humidity below the flooring, and the flooring for sure does not contact the concrete.

We need a humidity reading for the room and also for the wood floor. An independent wood flooring inspector may be a good idea so you can prove what was done wrong. They usually recommend that over on the flooring forum.

No, I don't think the problem is affected by drying too fast.

Until you find a flaw in the construction I suggest you assume the water is entering at the walkout well adjacent to the damaged floor. Find a section detail of the edge of the interior floor under the door threshold. It looks to me like the bottom of the well might be at the same height as the interior slab which might present a difficult waterproofing challenge. Water might be getting high enough to get inside when you are not aware of it. I would have put the drain lower and put decking over it.

I would have expected a step down at the door for weather protection. It wouldn't take much of a rainstorm to drive water into the house either below the threshold or above it.

I don't understand the water table photo.

Can you find a section detail through this condition?