We are renovating a small (21′ x 34′) 1960s slab on grade cottage in zone 3C. I’m sure it’s not insulated under the slab. I’m trying to decide how to install our flooring (wood and tile) over the slab floors. A few details: 

* Previous owners had vinyl tile directly set on the slab, and then someone added bamboo flooring over it with a thin, 3-5mm thick sheet of foam below the bamboo. We removed flooring down to the slabs. We didn’t see mold under any of the tiles. I also performed a moisture test (taping down 2’x2′ squares of thick poly over the slab to see if there was condensate. There was not).

* The home is about 60 ft above sea level and built on mixed clay soil. 

* The ceiling heights are only 8’1″ when down to the slab, so any floor assembly should be as thin as possible to maintain ceiling height. 

I’ve been looking into getting 3/4″ Dricore tiles that include XPS and subfloor, and then putting 1/2″ wood floors on top. In reading several articles about whether poly is required, I feel that in this case, we shouldn’t use it. I worry about moisture beading on the side of the poly that’s against the slab. In reading forums for Dricore panels, many ppl say that they don’t add another moisture barrier under the tiles. Some who did complained of mildew issues. From some reading, it does seem like there are times when moisture needs to move, so moisture retarders in this case are better than barriers. 

Recommendations on our how manage our flooring to prevent any mold issues would be greatly appreciated.