Mold on the inside of the basement wall?
Some time back I put some thought into the insulation strategy for my basement wall, see this link:
As a result of that discussion I was planning a mix of 1.5″ of polyiso rigid foam and blown in fiberglass into a 2×4 stud cavity.
We’re building a new home in climate zone 6A, steep uphill sloped lot in mountainous snow country.
My insulation guy is recommending I don’t use rigid foam as it becomes a problem for any moisture trapped between concrete and the foam With nowhere to dry to this trapped moisture will mold, he said. My contractor said that in many years time the exterior waterproofing of the concrete is likely to fail and so you need to plan for that situation and allow drying.
The first answer in my old thread by Michael Maines said that concrete doesn’t really need to dry at all and is not affected by moisture which makes sense to me.
Per Joe Lstiburek “I made a mistake. The insulation just needs to be warm enough to control condensation from the inside. The perm rating doesn’t matter. It’s OK for the concrete to be wet. The concrete doesn’t have to dry to the inside.”
Okay so it sounds like it is okay for concrete to be wet but how does mold not form?
Put another way my question is will I have a mold problem if moisture is trapped between the foundation wall and my foam?
There was a good reply from Dana in that previous thread explaining a few techniques I could use to allow the concrete to dry to the interior (dimple mat, stop foam short from slab, more vapor permeable foam). I’m trying to decide if an interior drying strategy is necessary or not.