An above grade portion (wood framing) of my basement walls (in unfinished furnace room) is currently insulated with faced R19 fiberglass batts. I live in nothern climate zone 5.
Unfortunately there is currently nothing but wood behind these batts and there is no air sealing, so when i looked behind the batts the wood walls have frost on them and some are soaking wet.
Before:
Before (behind faced fiberglass batts):
I begun a project to air seal behind the batts gluing 1" R5 XPS foam boards to the wood and spray foaming around the gaps, then removing the face from the batt and replacing the unfaced batt on top of of the XPS.
After:
After a few cold days i looked behind some of the batts that I had replaced and noticed that there was some condensation on the XPS foam boards (towards the vertical center of the boards). The boards themselves didnt feel cold at all.
Is there something else i should have done to prevent this / how can i correct it?
Thanks
Best Answer
The water is coming from the air inside the room, not from outside. It is condensing on the colder surfaces on the exterior walls (even if they don't feel cold). What you are doing is fine, it will block any air seepage and add some insulation value, but won't stop the problem you are having. What you need is a vapor barrier on the interior surface of the insulation to prevent the moisture in the room air from coming into contact with the colder layers of insulation inside the wall and condensing.