How to insulate and finish basement when there are signs of efflorescence?
I am re-finishing/insulating my basement in a 1930 home in Zone 4 (Pacific NW). I am planning to do it as follows from foundation to interior which meets local building code: Basement Concrete Foundation Wall > 1”XPS Rigid Board(Pink Owens Corning) > 2×4 Studs against the XPS > ROXUL insulation in stud cavities > Sealed Poly Vapour Barrier > Drywall.
There is evidence of white efflorescence on the basement walls indicating that there may be or has been in the past moisture seepage. There have been no flooding events. Being a 1930 house, the foundation is not waterproofed.
When i pulled out some walls from a previous renovation from the 90’s there was poly vapour barrier against concrete foundation wall, 2×4 studs with some loose foam board, another layer of poly vapour barrier and then drywall. The foundation wall was damp but there was no mold or rot.
I have a few question i am hoping someone can help with:
1. Given the efflorescence is it required to clean off and seal with waterproofing on the interior (Xypex or Drylock)? Excavating and waterproofing exterior is not an option. Old framing is still up so i would need to work around that.
2. Or can i just install XPS board directly against the wall? Or could that lead to mold?
3. When installing XPS does it require a seal on top and bottom edges using foam can spray seal? (Joints will be taped) Should it be airtight or is it ok/better to let some air flow in behind XPS board to let wall dry out?
Any feedback greatly appreciated.
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