Quote:
Originally Posted by pseudoreality
Can you elaborate a bit more on why the floor buckled? I am doing a similar job in my basement, but my floor is going to be a HDPE dimpled membrane (delta floor), then 1" SM XPS, and then I was going to build the walls, then sub-floor. I'm wondering if I'm going to be having any problems here.
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Any moisture will make the subfloor change shape. Usually this isn't a problem because people put it on regularly spaced joists and fasten them securely. When moisture levels change the joists and the subfloor both change shape. Just floating it over masonry provides not reliable means of fastening it. This is fine if you first fasten the bottom plates (pressure treated) to the masonry and then "float" the foam and subfloor between the walls leaving a 1/4" gap to account for expansion and contraction. My floor bowed and I used Advantech which is waxed in some way to resist moisture, so I can't imagine what regular subfloor would do. I ended up buzzing grooves in my floor to relieve the pressure. If I had to do this again I would fasten the walls to the slab with a powder nailer. I don't think it's a good idea to put the top plates on foam which is on something like DryCore or anything like that. It won't be able to support weight and the wall will sag eventually. Also you'd have to seal the foam to the foundation walls with something that won't dry up and crack when the foam moves (no product I know of. Maybe a Siga tape?) or else there's not point in the insulation board.