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I'm going to install a basement subfloor. I want to follow option 3 from this site: http://homerenovations.about.com/od/additions/a/BasementSubfloor.htm.

A nice option because the foam insulation provides an excellent thermal break between concrete and flooring.

Finish flooring.
Plywood screwed down through the layer below.
Rigid foam insulation - 1 1/2" thick.
Concrete basement floor. 

For the rigid foam insulation I wanted to use XPS foam. My question is, do I need sleepers for this? I saw on YouTube someone using a similar solution but they used sleepers under the plywood and filled the space between the sleepers with foam.

Thanks, mj

  • Good question. I think the sleepers would be important if there will be a wall resting on the floor. But otherwise, it seems unecessary IMHO. – DA01 Oct 30 '15 at 17:06
  • I've been thinking about that for my workshop, unfinished. Supposedly the foam can handle the weight, and it'd be an easier (though sloppier) solution than putting a french drain around the interior for the occasional infiltrations (which should still be addressed). I'm looking at a foam system for the walls anyway... – keshlam Oct 30 '15 at 20:03
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Yep, you can go with sleepers or with DA01 & Keshlam's concept while using tongue & groove plywood only. A variation between the 2 is to not do sleepers to keep the plywood flat but to do batten boards under the plywood seams with strips of plywood...you'd lay 1" or 3/4" thick insulation strips under the battens, depending on your plywood thickness.

This maximizes the thermal insulation & regular edged plywood can be used. 3/4" plywood would be more resilient if you envision heavier furniture. An aquarium, hot tub or weight lifting area would need full sleepers beneath the plywood.

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