I'm working on a project where I need to lay down a 3/4" plywood floor in my basement, which has a concrete foundation. I'm using pressure-treated 2x4 sleepers for support. There's occasionally some moisture that seeps up during heavy rain, but there's rarely any pooling, and the dampness usually dries out within a few days. I've come across suggestions online about putting down plastic sheeting either under or on top of the sleepers, but I have my doubts. If I place plastic under the sleepers, would it trap moisture and cause mold? Can concrete even grow mold? I'm leaning towards putting the plastic on top of the sleepers to allow airflow, especially since I plan to leave the framing open on two walls. The space will be climate-controlled, and I'm also planning to use a humidifier. What are your thoughts on these approaches?
1 Answer
I've got a shop in a detached garage on a concrete slab, and I faced similar issues with moisture. Here's what worked for me: I first tackled the water leaks, then I laid pressure-treated sleepers on the concrete, filled gaps with Styrofoam insulation, placed a moisture barrier, and finally installed my subfloor. Make sure the moisture barrier is on the warm side of the insulation to prevent condensation from forming on the inside. It’s been over 20 years, and I've had no problems—it’s comfy year-round!
That sounds like a solid plan! I wonder, though, will you be using insulation between the sleepers? I’m considering it for my project, but budget is tight since we’re a non-profit makerspace and just spent a lot on the materials.