Why is there condensation above ground on an interior basement wall?

B

Why is there condensation above ground on an interior basement wall?

Barb Daluisio Published: Jan. 12, 2021, 1:26 p.m.Last updated: Jan. 13, 2021, 8:05 a.m.

My husband is finishing our basement and installed 1 inch foam insulation to the exterior wall before framing and then installing fiberglass insulation. When he began drywalling he noticed moisture behind the fiberglass on the secrion of the wall that is above ground. At this point we are wondering what we could do to remedy this. I should mention we live in the northeast and it has been very cold of late.  Since it is on the part of the foundation that is above ground, is there something we could do to the exterior wall to prevent this? The foundation is damp-proofed below gound already on the outside so it seems the issue is condensation from the cold air. What can we do...help!

Responses (1)

Andrew Cole
Andrew Cole Jan. 14, 2021, 9:06 a.m. Reply

Concrete is a known heatsink. It will be hold heat for a longer period but will also hold cold too as the seasons change. Exterior mechanical insulation is not the best as it is hard to guarantee air tight bonds when installed. So as you have warm air in your basement and the concrete is cold do to the outside exposure it will create a dew point temperature differential. As you add the fiberglass you create the condensation space for the air to cool and the humidity to condense.   2lb. closed cell Spray foam is an excellent alternative insulation as it will bond directly to the concrete during the site installation creating now airspace between the foam and the wall. The R value of the foam will eliminate a condensing surface.