How much of a gap do I leave between the wall and the OSB I am putting down on the concrete for a subfloor?

Question

I am putting down a product similar to the plastic used on the DriCore 2x2 sheets on the concrete for a vapor barrier. I have 3/4" tongue and groove Oriented strand board (OSB) I will be laying down on top of it. We will be carpeting over this. I have drywall up that is 1/2 off the floor. How much of a gap should I leave, and should I anchor the wood into the concrete?

I should add that this is in my basement. We moved in, the walls are up but they had carpet glued to the floor. I pulled out the carpet and want to put in a subfloor (above) but am not sure if I should leave a gap or push the wood up tight against the wall.

Answer 1

I did the same thing in my last house, using DeltaFL and 4x8 sheets of OSB.

Spacing

I used spacers to leave a 1/4" gap around the outside, and then framed all interior walls on top of the subfloor.

I had laminate installed on some of it, and carpet on the rest. I can attest it's a great way to do a floor as it has the feel of an upstairs floor. I lived in that house for 4 years without any issues whatsoever.

Screws

I screwed it all down, and ended up using at least 24 tapcons per sheet. My floor was really quite level, but any minor variation meant when you walked on that spot you could hear the clicking of the plastic sheet, so for a couple weeks after I had it installed I was still finding 'clicking' spots and adding tapcons.

The downside: it's backbreaking work. I would definitely invest in a rotary hammer drill. I helped a friend do his the same way, and we had a rotary drill that time, and it could do 4 or 5 holes in the time a normal hammer drill can do one. Total install time was about 10 hours to do around 900 sqft (including everything) with 3 guys. I did mine mostly by myself working a couple hours every evening, about 350 sqft, and it took me a couple weeks.

Answer 2

Do you have a roof over it yet?

The American Plywood Association (APA) has guidelines that suggest 3/4 inch, but that's based on up to 80 feet of floor between joints and expansion due to rain and wetness during construction. They suggest gluing the tongues and grooves together, at which point attaching to the concrete seems superfluous.

If in a dryed in space, you might go with a bit less and be just fine. The DRIcore product that you are not using, but which is similar to what you are doing, suggests 1/4"