Basement – Do I need so many fasteners and an edge gap for a basement subfloor on concrete

basementmoisturesubfloor

I'm getting ready to install subflooring in a residential basement, which currently has exposed concrete slab. The concrete is well-cured (50 years) with no moisture problems. The plan is to lay down 6 mil polyethylene sheeting, followed by 3/4" AdvanTech subflooring. I plan to use Tapcon screws to fasten the subflooring to the concrete.

Some of the installation guidance I've received seems like overkill. Can anyone with more experience weigh in?

  1. The fastener pattern for each 4'x8' sheet of AdvanTech requires 52 screws, if my math is correct. Do I really need that many?

  2. Someone mentioned that the poly sheet should be glued to the concrete slab. The only reason I can think that would make sense is to keep it from sliding around during installation. (If I really do want to glue it down, any suggestions on a good adhesive?)

  3. Depending on who you ask, there should be a gap of at least 1/4" to 3/4" between the edge of the subflooring and the nearest vertical obstacle. But if the fastener pattern is every 6"-8" along the edges of each subfloor sheet, how could the AdvanTech ever shift/swell enough to require that much clearance?

  4. After I drill the holes for the Tapcon screws, some people suggest squirting roofing caulk (or similar) in the hole before inserting the screw. I think the idea is that it helps restore the integrity of the moisture barrier system around the screw hole. Would that be overkill in this basement?

Best Answer

  1. Do you care about the manufacturer's warranty? If no, no. Do you need the moisture barrier, or can you use a small-bead adhesive bond directly to concrete? If no, and previously no, no.

  2. I agree. It would serve no real purpose otherwise.

  3. I agree, but see point one, sentence 1. You'll want to shoot for 1/4" just for ease of fitment anyway, but much larger in a fixed subfloor seems pointless.

  4. Caulk splooshed haphazardly into a dusty hole will do nothing that the concrete itself and the screw threads aren't already doing. You won't end up with anything like a waterproof seal. That suggestion was made by someone who considers "seems like a good idea" as a threshold for viability. I don't.

Disclaimer: This answer is entirely opinion, based on extensive experience, but opinion nonetheless. The question itself is borderline off-topic for that very reason.

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