Detailing a Slab in a Hot-Humid Climate
I’m in the process of finishing my basement and wanted to hear some opinions about floor assemblies. First some quick info: Climate zone 3a, poured concrete slab, 9′-6″ ceiling, no insulation under slab, no bulk water issues so far, new house constructed in 2016.
Based on what I have read in these forums and on Fine Homebuilding, I thought my floor assembly was going to be: slab>3/4″ rigid foam (seams taped)>3/4″ OSB (secured to slab w/ tapcons)>finished floor of engineered wood or LVT.
However, I have seen some sources suggest using a air gap membrane under the OSB subfloor, similar to a Delta FL or DMX. Would this take the place of the rigid foam? I can’t imagine an assembly with both of them, so is there an advantage to either approach? In my climate zone I don’t think any insulation is required under the slab, any my primary intent of using the rigid foam above was to reduce the risk of moisture problems (condensation), not necessarily comfort…though that would be nice.
Also, I did not plan to put a layer of poly down between the slab and either assembly, because there is one under the slab. Bad idea? Poly is not that expensive of course, so if it would help, then its something I would probably include. I just wouldn’t want it to complicate any of the approaches listed above (I think Martin mentioned an imperfect knowledge of building science creating big problems in the FHB podcast…makes me cautious).
Anyways, would love to hear folk’s thoughts about the two approaches and what would work best in my relatively warm, humid climate.
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