This is the first house I've lived in with a basement in 20 years. Having both grown up in the North East, my honey Wino and I both know the benefit of having that living space available for things you might not want in a spare bedroom, like a "rec room" (that's what we had growing up) or a wine/beer lab, or a music studio. So Wino was thrilled that there was a basement and that it seemed already finished. Ha! Not so! Due to some serious carpet abuse by the previous tenants' pets, it just had to come out. That's when we realized it was merrily glued to the concrete floor, with no subfloor or anything. The carpet had damp spots and I wondered if those were to be blamed on untrained pups or moisture wicking up from the concrete. So the search for suitable subfloor commenced. Normally, one would lay a plywood subfloor but it would need to be raised, commonly with 2x4 joists. The ceiling is a bit low (7') so I didn't want to lose even more headroom. The Home Depot sells a basement subflooring system that is 2'x2' tiles of OSB plywood with plastic spacers on the back to raise the floor slightly and give it "vapor room". The theory of "vapor room", which is a term I made up to try to explain it to Wino, is that the concrete gives off and absorbs moisture but if you can create a space where the vapor equalizes above the concrete, it won't continue into the room in the form of humidity and condensation, thereby making the concrete happy (less cracking?) and the basement happy (less damp, more stable temps). I wanted to use a laminate for the finished floor so whatever I used needed to be compatible with installing that flooring type. The Home Depot product seemed like a winner but the cost per sqft was a bit much, upwards of $1.70. And I envisioned a good deal of waste due to the size. So I continued the search and found a subflooring system that we ended up using called Cosella Dorken (oh, the Germans, we love them). For about $.65 sqft, it seemed like a good choice but I was skeptical. It rolls out in a sheet so install is relatively quick, you can walk on it right away and we put a 1/8" foam underlayment then installed the laminate right on top. This reduced our headroom by only 5/8". I was happy with the product but you need two people to install it unless you have weights handy, it wants to roll back on you, making it hard to measure and place. Now here's where I went wrong. The seams need to be taped with their special vapor-sealing tape. I bought one roll, doing the math and figuring it was more than I needed. As so many thing turn out, I ran out of tape and ended up using heavy duty packing tape to finish some smaller seams. I also failed in making the flooring snug to all walls like it says in the install guide. I'm not sure how much this will affect the "vapor room" but I guess time will tell. If you want to install carpet with this product, you must lay a wood subfloor over it first, but using OSB is fine and a little cheaper. Then you can lay ceramic tile or carpet, I bet you could even put electric radiant floor heat if you were really motivated. Having the subfloor under the laminate definitely keeps the flooring from getting super cold and the basement stays about 56 degrees without any heat on. Not bad when it's 15 degrees outside.
Here's some tips on installing this subfloor: make sure the floor is clean and as free of dust and schmutz as possible. We washed the floor with a mold preventative before putting down the subfloor since we found mold on the carpet. This was just a precaution but it made me feel better. I also sealed the cracks in the concrete with concrete caulk, forcing it into the crack with a paint tool. There was a good deal of glue residue and foam crap adhered to the concrete and I scraped up as much as possible without losing my mind. The flooring is relatively forgiving so just get the big bumps (anything over say, 1/16"). Lay it out along the longest wall, weight the ends and cut it a row or two longer than what you think. let this curl up the wall, you'll trim it later when the laminate starts to go in. Our first row was 32' long and when the flooring went on top flattening it, there was a little space at the cut end where it didn't snug up to the wall.
I would recommend this subfloor since it was a good price and installed quickly, about 4 hours for 625 sqft. It was thin and the height difference is unnoticeable. It's definitely a good solution to subflooring a basement.