Building Science Corp. advises
that "carpet should not be installed directly over an uninsulated
concrete basement slab. Any moisture that condenses on the cold slab
becomes a nice habitat for mold and other biologicals."

That said, I have installed synthetic commercial flat pile carpeting directly glued to the concrete--no underpad--with no problems. But once you use an underpad, it will inevitably trap moisture that is always rising through the concrete due to moisture drive. It doesn't take long for the mould to start growing, compounded by the fact that many/most homeowners still don't use dehumidifiers.

Thanks for the input.. We are trying to looking into the best method of doing this.. The more I think about it, the more I think carpet is the way to go.. Tile would probably be the most "durable" in the event of a flood.. But we can play the what if game all day.. I have done some research online and the two methods that I have found are either A) put down a 6mil vapor barrier, then carpet pad, then carpet or B) put down dimple pad (DMX 1 step or similar), then plywood/osb board, then carpet pad, and then carpet..

Basically from what I have read Option A is if you have a dry basement and Option B is if you have some moisture and/or uneven floors.. I am considering going with option B as a precautionary measure.. But we will probably be bringing in a contractor that specializes in basements..

Option A only works if you are in a desert zone. (None in NJ that I know of.) Otherwise--unless you have insulated under the concrete--there is always a pressure drive, high to low, that brings moisture into the basement. Any moisture under the plastic sheeting will condense and has to go somewhere. In the meantime, it remains to feed mould growth under the plastic.

All the various Options B work well. Here's the schematic of Building Science's XPS version.

The downside is that all the precautions to make carpet work without mould problems is that the cost can be the same or more than tile alone.

we will probably be bringing in a contractor that specializes in basements..

From what I've seen over the years, you know more than many of them do already!

Well the house is a new construction home.. For basement waterproofing we have the following (which contractor said was overkill):

1. Rubber membrane sprayed on all exterior below grade walls to ensure water will not penetrate

2. 2 inches of XPS rigid foam insulation over the rubber membrane on exterior of perimeter walls

3. Dimple Pad over the xps insulation to flow all water directly down to base of foundation

4. Exterior perimeter drains around entire foundation at base to flow water to sump pumps

5. Interior perimeter drains around perimeter of basement to flow water to sump pumps

6. Vapor barrier under concrete slab to help with moisture penetrating through

The only thing we didn't do (and I regret) was putting rigid foam down under the slab....

Well done! Are there special concerns you had? If not, on one hand, it is a bit of overkill. On the other, the extra membrane and drains are peanuts compared to the cost of re-excavating and redoing.

Rigid foam under the floor will save a bit on heating costs but is most useful in reducing dampness in the summer months. Less dehumidification is needed. I was debating it on a new build. But at $C27.58 including tx. for 1"x4'x8' sheets, that's $C2,592.52 under the 3,000 sf footprint. It's an invisible benefit that's hard to sell!

Thanks. We had some concerns as we built on a hill and have family on same block that had flooding in their below grade basement. So we took pretty much all precautions.. Turns out that a "friend" did their extension that included the below grade basement and basically no waterproofing measures were taken which is why they get water.. We have been living in house since April and have had many bad storms and still have yet to hear the sump pumps kick on.. And not one ounce of water (knock on wood) has been found in the basement.. We currently have the hvac for first floor hooked up in basement so it is a conditioned space already.. Just doesn't have its own zone.. We haven't noticed any odors coming from basement.. Going to throw a unit down there to measure humidity and also going to try the plastic taped to walls and floor test.. i guess we can go from there and see what happens..

I'm also in NJ and considering our options for carpeting in a newly built basement. What have you decided to do?