Just a bit of background before I get into the potential issue. I live fairly far north and have a basement with concrete foundation walls (not block). In the winter, we can get air temps as low as -35C or so. The house was built in 1999, and the basement is currently framed, insulated and vapor barriered - it has been like that for at least 7 years, and more than likely for 16 years. Metal framing, R12 fiberglass insulation.
On to the potential problem. I am looking to actually finish the basement, and was curious if the builder had put any rigid foam against the foundation, or if they just left an air gap. The vapor barrier wasn't sealed to the bottom plate - it was just draped and hung there, so lifting it up to look behind the insulation wasn't difficult. Turns out it was just an air gap, but the concrete itself looked like it had quiet a lot of block mold on it. The insulation seemed dry and free of mold.
I suspect that the concrete has mold due to condensation from the warmer basement air getting underneath the vapor barrier. What I don't entirely understand is why the insulation wasn't damp and moldy as well.
Does it make sense that the concrete is moldy and the insulation isn't, given what I described above? Or is there something else going on?
If it is mold, I intend to have anything removed and cleaned properly and am thinking that this would be what I'd do, in order from foundation wall outwards. 2 inch rigid foam (glued w/ PL300), bluwood or pinkwood framing (w/ sill gaskets against concrete), and roxul comfortbatt insulation (R14), vapor barrier, 5/8" drywall. Also debating 2 inch Roxul Comfortboard IS instead of the foam. Does that all make sense?
I appreciate any insight, advice or suggestions - I've only been researching proper basement insulation/building envelope type stuff recently when I decided to finish my basement...
On to the potential problem. I am looking to actually finish the basement, and was curious if the builder had put any rigid foam against the foundation, or if they just left an air gap. The vapor barrier wasn't sealed to the bottom plate - it was just draped and hung there, so lifting it up to look behind the insulation wasn't difficult. Turns out it was just an air gap, but the concrete itself looked like it had quiet a lot of block mold on it. The insulation seemed dry and free of mold.
I suspect that the concrete has mold due to condensation from the warmer basement air getting underneath the vapor barrier. What I don't entirely understand is why the insulation wasn't damp and moldy as well.
Does it make sense that the concrete is moldy and the insulation isn't, given what I described above? Or is there something else going on?
If it is mold, I intend to have anything removed and cleaned properly and am thinking that this would be what I'd do, in order from foundation wall outwards. 2 inch rigid foam (glued w/ PL300), bluwood or pinkwood framing (w/ sill gaskets against concrete), and roxul comfortbatt insulation (R14), vapor barrier, 5/8" drywall. Also debating 2 inch Roxul Comfortboard IS instead of the foam. Does that all make sense?
I appreciate any insight, advice or suggestions - I've only been researching proper basement insulation/building envelope type stuff recently when I decided to finish my basement...