Hey everyone! I'm facing an issue with water accumulating behind the vapour barrier in my newly built basement. The house was completed in 2023 and I've just moved in May 2024. I went down to check on the finished basement and noticed a damp smell. When I looked beneath the stairs, I found water trapped behind the vapour barrier, which I suspect is causing the smell. I've attached some pictures for reference. The exterior wall appears to be the foundation with insulation and a plastic vapour barrier sealed to the studs. After pulling back the barrier, I removed the wet insulation but didn't see any active leaks. The basement is pretty cold at 17-18C (about 63F) and the humidity level is high at 88% where the insulation was. I'm considering leaving it to air out, but I want to know what my next steps should be. Besides replacing the insulation and barrier, should I check for leaks after rainfall or do something else? Any advice would be super helpful!
4 Answers
You might be dealing with condensation issues. Since your basement is conditioned and colder than the outside, warm air hitting the cold wall can lead to moisture buildup. The vapour barrier may not be perfectly sealed, allowing condensation to form. I suggest sealing any gaps and considering closed cell spray foam for better insulation and moisture control.
It sounds like you're dealing with a pretty outdated insulation setup. The foundation might be pulling moisture from the damp soil around it, which could lead to condensation behind the vapour barrier. If you’re after a solid fix, I’d recommend removing the whole setup and going for closed cell foam insulation instead—it's more effective and acts as a proper vapour barrier too.
The vapour barrier seems to be letting moisture through, a common issue since houses started getting tightly sealed. All that trapped moisture needs somewhere to go, or you're going to face mold in the long run. I'd suggest waiting for a heavy rain to see if more water comes in, but you really need to figure out the moisture barrier placement on the outside to stop the problem at the source.
Ugh, sounds like a lot more work than I anticipated! Thanks for the insight.
You should inspect your drainage and gutters because water pooling next to your foundation could be contributing to this problem. If they’re not directing water away properly, that’s definitely an issue. Also, check that the vapour barrier is sealed tight—leaving any openings can lead to condensation problems like you’re seeing.
Thanks for the tip! Sounds like I need to tackle those gaps before the next humidity wave hits.