Insulating over concrete floor
I’m working on a renovation of a 1928 house. It has a basement with a poured concrete floor, no insulation. I would like to get it to at least R10. Because of the high embedded energy and greenhouse gases of concrete, my preference is to leave the existing floor if I can.
The thought I want to run by the experts here is to put sheet insulation over the slab, then a layer of Advantech and a finished floor. I’m thinking of just putting the Advantech down as a floating floor, held together by the tongue and groove. When I’ve done floating finish floors I’ve gotten excellent results screwing down the first row so that I can really pound the floor together. With this floor I would TapCon to the concrete all of the pieces on the perimeter. One concern is that Advantech only has T&G on the long edges which may cause the short edges to move. An alternative would be to put down 1/2″ OSB covered by 1/2″ luaun. The joints would be offset and short deck screws would hold it all together.
What do you think of that idea?
Two bonus questions:
First, what sort of insulation to use. EPS is the obvious choice, but would have to be 2 1/2″ thick. Polyiso would only be 1 1/2″ but I’d worry about moisture, a basement is a basement. A wild card is Roxul board, according to this article ( https://www.greenbuildingadvisor.com/article/sub-slab-mineral-wool ) Roxul now recommends it for horizontal applications.
Second question is how to do a vapor barrier: below or above the insulation? Just 6 mil poly sheeting? Should I try to make it absolutely watertight? If so, would it make sense to use something like ice and water shield where the tapcons are going to go?
Thanks.
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Replies
DCcontrarian,
Just a suggestion, but you might want to click through the related links located on the right side of the page. Most of the issues you are wrestling with are addressed in these articles and threads.
Hi DCContrarian.
I've never heard of anyone relying on the tongue-and-groove edges of subflooring to hold a floating floor in place and I think you answered your own question when you noted that the short ends of the sheathing don't have this joint. You could mill it to the sheets easily enough, but I'm skeptical of this idea.
You should either use one layer of Advantech and screw all of the sheets down or install a floating subfloor with two layers of plywood or OSB, screwed together with staggered seams, in my opinion.
EPS is a good choice. Place the poly vapor retarder between the slab and rigid foam, if you use it. I suggest reading this: Installing Rigid Foam Above a Concrete Slab. It will give you in depth reasoning for your choices.