Extruded Polystyrene Insulation under 5/8" plywood

Hi, I have been reading for the last several hours since finding this forum - what a great resource! I have also purchased and read Rod's book which is also incredibly useful. I am building a studio in the basement of my home and in all non-studio areas of the home we are installing 1" Extruded Polystyrene Insulation on the concrete floor, followed by 5/8" plywood held down with Tapcons. We are doing this for comfort and warmth. My question is, would this act as a floating floor if I applied this in the studio area (and I realize a floating wooden floor is not recommended) or would it act as an extension of the concrete due to the rigid nature of the foam? The foam is manufactured by Owens-Corning. I due not want to create a true floating floor and there will not be any air gap. thanks Calvin

Thanks for those who read my post. I am laying 1" Polystyrene Insulation onto a basement concrete slab, and putting 5/8" plywood directly over that and fastening to the cement with Tapcon screws. Will this cause any problems with sound (i.e. am a causing a resonant frequency problem)? If so, I will stick with the concrete slab in the studio portion of the basement. thanks Calvin

Hottracks guy wrote:

. . . or would it act as an extension of the concrete due to the rigid nature of the foam?

I could be wrong here (although I think I'm right ;-))... But it would seem to me that you would have a one leaf system with that approach. I think it would accomplish your goals for comfort but not do anything substantial for isolation. Resonance? Maybe... Using two layers of plywood over the EPS with Green Glue sandwiched in between them would most definitely address that. I wouldn't plan on building inner leaf framed walls upon that surface though... :roll: --Keith :mrgreen:

Thanks for your reply. That was my plan so perhaps I should just stick with the concrete pad for the studio area, and put carpet down. This gives me a little more headroom as well since I only have 7'6"" to bottom of floor joists. Calvin

Check with your local building department about minimum vertical clearance for basements, emergency egress requirements (if any). One idea to save headroom is to do an etched stain on the slab.

thanks again. I will definitely consider that and will look for more advice on etching when I get close to finishing. I appreciate all your help. Calvin