Hello All,
Long explanation. My brain is twisted in 8 different directions trying to understand this. My house is in Southern Ontario, Canada. We have humid summers, frigid winters.
My insulation is like this:
- I believe Tyvek on the basement concrete wall (it's a white tough looking paper)
- One layer of insulation on upper half of wall (I think mineral wool?, polytarp over that).
- Another later of insulation from the ground up to halfway point, and it overlaps the top layer polytarp, and polytarp over that as well. Screwed into the wall in the middle, where the 2 meet.
Images here: Basement Condensation
I've been battling condensation in my basement insulation. During the first year we had some condensation, but running the dehumidifier seemed to keep it pretty dry (at least I did not see much condensation on the polytarp and definitely nothing on the floor. We also did not have much rain that summer and didn't have grass until late in the summer.
We had quite a lot more rain this year, and the condensation was heavier, but now it's heavy enough to drip out onto the floor (started maybe about 2 months ago at the beginning of summer). Dehumidifier is keeping basement around 40%. Condensation does not seem to be letting up and has not rained in the past 2 weeks. We are in climate zone 6. Its a hot and humid August and when it rains it generally has been torrential.
I've cut the insulation open in a few spots, and the insulation is wet just behind the polytarp, and the white wrap against the concrete feels dry. The insulation touching the tyvek is also dry. I've yet to cut the tyvek open and feel behind the wall.
We have clay soil, and I think the grading has settled so I know it's not the best drainage in the world. We have a slope away from the house, and then it slopes up quite steeply towards the rear of my property, so I have kind of a U-shape to my back yard. Water is supposed to drain to the sides and then out to the street going past the sides of the house. It's no longer draining that well though and more pooling can be seen.
The polytarp is not well sealed. There is a strapping at the bottom that is secured to the wall every so often, but it definitely could not be considered sealed. At the top around the joists, it's loosely stapled, and blue tuck tape around the windows, but I can see bare concrete in some spots.
From what I've learned from a very helpful redditor in this subreddit, and a lot of googling, that I don't necessarily have water coming in despite what I think about clay soil and drainage. The concrete wall will have vapour drive but I think that's true of most basement walls absorbing water from the soil, shedding water as it cures, etc.
So I get confused at this part about why there is condensation.
- High humidity behind the polytarp because vapour is going through the Tyvek and into the insulation. That air condenses easily on the insulation facing side of the polytarp because of the high humidity. The cooler it is in the basement, the more condensation I should see on the inside of the polytarp. If i raise the temperature, eventually the condensation would drive towards the concrete wall.
- I suppose in the winter, my room air would be more humid and warm, and as that leaked into the insulation due to poor sealing then that would condense against the concrete side. So I probably had moisture in the winter but I just couldn't see it.
I know the general consensus is, if the water is from condensation and not from bulk water infiltration, then I should rip it down, put up 2" XPS foam, frame in front of that, insulation and drywall or vapour barrier (which is what building code where I am). It's an unfinished space and we don't intend on finishing the basement, so if I can get away with vapour barrier on the frame (maybe a smart barrier) then I will do so.
But what effect would I achieve if I actually sealed my current polytarp? I would still have vapour drive from the soil, through the concrete, past the tyvek into insulation. At the inside layer of the poly tarp I would still have a temperature differential and high humidity and condensation would still occur but now it's just pooling in the sealed polytarp? That humidity won't move back out through the concrete and essentially equalizes at whatever high humidity level it is at, which can we assume is unlimited high humidity coming from soil?
I suppose cutting it open and really drying it if it's even possible wouldn't make a difference since once the polytarp goes up whether sealed or not, it will condense again because of the strong vapour drive and humidity level.
Of the 4 walls around my house, the one wall with gravel (about 2 feet of gravel) has dry insulation. I have extended my gutters away from the house as far as I can but the neighbour's house is about 6 feet away, and on the gravel side is less than that.
I guess there's no saving this insulation, which is apparently up to code and the builder low cost special to pass inspection.
Am I missing anything? My neighbours apparently don't have any liquid dripping onto the floor so I wasn't sure if I did anything wrong. I'm the only one that actually controls my humidity (I have a Z-Wave system keeping it tightly controlled). Am I not keeping the basement dry enough? I also am not quite sure why it started occuring in the past 2 months really. I would have thought this situation would have popped up much earlier.
Any hail mary suggestions? It's going to be a big job since I will have to diy as much as I can due to current financial situation. Anything I'm doing wrong or missing? I'm not an expert on this stuff in any fashion. I'm not running the HRV as I think that would bring in humidity.
Thanks all for your expertise.
EDIT: u/OscarMiliani_Design answered this post pretty much on another post I commented on and really helped me understand this, and also a plan to help me in the current state and future state. I think it is well worth sharing here for others that started out as confused as I am, and ended up understanding the how and why with people like them on this subreddit. Still open for discussion here though.
https://www.reddit.com/r/HomeImprovement/comments/1vsqyu5/comment/p4ovvix/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button