Framing basement walls and basement subfloor

Hello everyone,

I am asking for people's opinions on the project I'm about to tackle for framing and flooring my unfinished basement.

I have one alcove that is an 18'x20' section that I am going to turn into an exercise/office area.

After doing much research online, the obvious first step is to fix any moisure or seepage problems.

Some background:
I bought this house 4 years ago from my grandfather. The house itself is almost 30 years old. Since I've lived in it, only one time I have seen water on the floor in this area 3 yrs ago during extremely heavy rain. Since that time, we've had the gutters cleaned, extended, (they used to drop right next to the foundation walls), and had the aluminum siding taken off, house wrapped in tyvec, new vinyl siding put on, and also a sump pump installed in another corner of the basement. I have not seen any water on the floor since though the concrete walls have evidence of water in the past. Some of it on the bottom is black. Is that just old water damage or mold? Since I havent seen any water in the last few years, I think its just old damage. I can't really tell. What is the best way to clean that?

I have a low ceiling height, exactly 85" (7'1" ) from concrete floor to the bottom of the floor joists above, I've decided to leave the ceiling unfinished. That also gives me easy access to any wiring or plumbing above if I ever need access. (also room for doing military presses with dumbells, ) Instead of finishing the ceiling with drywall or any kind of drop ceiling, I plan on just priming and painting the complete ceiling with flat black using a sprayer.

The approach that I'm leaning towards for framing the exterior walls would be to cover the entire concrete walls with 2" XPS rigid foam using adhesive, sealing the seams with tape. Then I'm going to use pressure treated 2x4 studs to build the framing and affix that to the concrete flooring and the ceiling joists. then run my electrical lines, and fill the stud walls with unfaced batt insulation. For the subfloor, I am leaning towards using Dricore panels for the entire room, leaving a 1/4" gap between the subfloor and the bottom plates of the framing around the room. For finishing touches, the walls are going to be drywall and the flooring I was going to use some nice thick underlayment and carpet.

Does anyone see any problems with that? The reason I picked Dricore it does provide a vapor barrier and breathing room for the concrete floor and it only takes up 7/8" (definately a plus, since I have low ceiling). Since my ceiling is low already, building a subfloor with 2x4's layed flat would take up too much room since then I've have to put plywood, etc on top of that.

I've read that a common approach is just to frame using 2x4s, put batt insulation in there, and then use a 6mil vapor barrior between the studs and the drywall. However, I've read a lot that said that this is actually terrible, a huge 'no-no' because the vapor barrier traps moisure and will cause mold and mildew in the walls. I've read the same about using any kind of sealing 'paint' directly on the concrete walls and that he paint actually feeds the mold. The best approach I've read about is 2" XPS rigid foam directly on the walls and sealed is the best for allowing the walls to breathe and not trap moisture. I choose to use 2x4 stud walls on top of the 2" foam as well so it leaves room for electrical boxes and gives me support if I was to mount anything heavy on the walls. However, I'll still be attaching the pressure treated plates of the walls directly to the concrete floor and then the dryall to the studs. Is that ok? At this side of the house, the ground level is only about 2 or 3 blocks up. Should I put a 6 mil vapor barrior about 3 blocks high between the 2" foam, wrapped underneath the wood plate, and back up the other side about 2-3 blocks high between the stud and drywall to prevent any moisure absorbing up the studs and ruining the drywall? I'm thinking that since it only 2-3 blocks high, that it would help prevent moisture absorbed from the concrete floor up the stud from damaging the drywall while also not trapping anything to cause mold.

What does everyone here think?

I have seen sprayed-on closed-cell polyeurethane foam used as a vapor barrier in a basement, with the studwall built and insulated next to that in the way you have described. Not a DIY project, but you might check out the viability for your case. As for the 6mil plastic vs the 1" foam board, I can't see where there would be any difference, as far as moisture is concerned. They would both act as vapor barriers, wouldn't they? If the plastic sheet traps moisture and encourages mold growth, why wouldn't foam board do the same? Seems like it is just a thicker plastic sheet. The foam board would obviously provide a bit extra insulation. I guess the type of foam would make a difference. I believe closed-cell is considered a vapor barrier, whereas open cell is considered a vapor retarder. I could be wrong on that.

The mold growth problem occurs when there is fairly constant moisture coming through the walls. Mold must have moisture and air to grow. A little occasional moisture that is allowed to dry out reasonably quickly should not be a problem with the 6mil plastic. The problem happens when the walls aren't drying out in reasonable amount of time, such as when the soil near the house remains saturated with water. If you have corrected the drainage problem and haven't noticed any further infiltration, you should be fine.

I have also seen walls painted with paint specifically formulated for sealing basement walls (after sealing any cracks with caulk). There are several brands on the market. The paint acts as a vapor barrier, keeping moisture behind the face of the block and out of the living space. In such case I would eliminate a plastic vapor barrier altogether, as you don't want two vapor barriers facing each other, since this, indeed, traps moisture between them with no means of escape. One thing about the paint that I don't know is whether the paint breaks down over time. The 6mil plastic will not.

If you have a recurring moisture infiltration problem, you need to install a foundation drain around the perimeter of your basement, with a small gap between the basement wall and the floor to allow moisture to drain out of the basement and flow to your sump, before you do anything else. Not your average DIY project either.