I am refinishing a basement and have run into a major issue with insulation and could use guidance from professionals. I am located in Delaware, Climate Zone 4A
My basement looks like this: Block Walls, then a perimeter French Drain along the inside of the wall, then an 8 inch air gap, then 2x3 framing. The basement is 7 feet tall, about 6 feet is below grade.
The basement was previously finished in 1977. They just had that crappy wood paneling nailed to the framing and that was it. No insulation, no anything. In this setup, the basement air felt fine although it did get cold in winter. I decided to remodel.
I tore out the paneling, and then spent about 2 months doing various repairs to the basement. During this time the air all felt just fine. This is an unconditioned space, no HVAC.
I was told by various contractors that when getting ready to put drywall up, I needed to add a moisture barrier to the block walls. So I used 6 mil poly sheeting, cut in 15 foot long lengths and attached them to the top plate of wood above the concrete walls. I overlapped the seams by 24 inches on both sides and did not tape the seams. I ran the sheet all the way down the wall and tucked the bottom into my french drain. I was told this is the correct moisture barrier setup since warm air from the room could contact the cold air by the concrete block walls, which would cause condensation to form, but it would form on the plastic, and then gravity would pull that moisture down the plastic into my french drain and it gets whisked away. After the plastic was up the room still felt just fine.
I then added R-13 faced insulation in the 2x3 framing. THIS is where ALL the problems started. After doing that, the basement started to feel AWFUL, just incredibly stuffy and super sticky and humid. The air felt heavy and even light exertion would result in sweat all over your back and forehead, where it hadn’t before. It was absolutely uninhabitable down there.
I had been running a 50 pint dehumidifier this whole time. So I put 3 digital temperature and hygrometer gauges in various spots around the room, and even though the room felt stuffy, sticky, and gross, bizarrely, all three gauges confirmed the temps in the room were a stable 66-68 degrees and the humidity was a stable 34%-36%. I know those are perfectly fine humidity numbers, but the room felt like walking around in a meat locker, you just got instantly clammy and sticky and the air felt super sticky and stuffy. I tried opening windows, changing the air with a fan, changing dehumidifiers, nothing helped.
So after days and days of having various HVAC techs some by and insulation people come by and scouring the internet and posting all over, I was at my wits end. I then came across this post on this forum by user Marcel Cyr, CMI (Basement vapor barrier - #4 by mcyr) which seemed to describe my layout pretty accurately for the moisture barrier, but said I should have used UNFACED batts.
The oddity of my basement seems to be the 8 inch air gap between the concrete wall and the framing. I read in several places that you should NOT insulate the top of that gap, and the air should be able to flow between the air gap and the room to help that air “dry into the room”. So with that open, air can freely flow into that air gap, which means moisture can flow from the room to behind the insulation easily. And then it seems like it got trapped there because it could not migrate back into the room through the vapor barrier. By using faced batts I was basically collecting and concentrating moisture in between the walls, which in my imagination could have 2 possible ways to make the room feel sticky:
The humid air from between the vapor barriers migrated into the room through the top or access holes, making the living space feel humid
The normal humidity in the air was trapped in the living space since it was basically encircled by a blanket of more humid air along the perimeter of the wall so it could not migrate and flow.
In either case I would think that would register as high humidity on my hygrometer though. But going along this line of thinking, I tore the paper facing off the insulation (turning the faced batts into unfaced batts). I left it overnight and checked in the morning, and in the morning, there was definitely a change. In short, the stuffiness seems to be gone/greatly diminished. The room feels cooler and more “airy” if that makes sense. The feeling of “heavy air” is gone. But, the stickiness is still there, I think it feels a little less intense. It is hard to tell as this is all subjective. My hygrometers all show the same readings, which seemed odd, the only difference is the temperature uniformly dropped by 1 degree to a steady 63 vs 64 across the room.
As an experiment I put one of the hygrometers back in the 8 inch air gap, and surprise surprise, it went up 10% to 45% vs 35% in the rest of the space. So it seems like I found the mystery humidity, it was building up in the air gap, creating an envelope of humid air around the room. That seems to have prevented the normal course of air flow around the room, creating a “bubble” of stale air in the living space surrounded buy warmer, more humid air.
That also means that the insulation was up, with the vapor barrier, for 8 days and building up humidity in the air gap between the insulation and moisture barrier. I would think that now needs to dry out. In order to promote the drying out process, I pulled the top 1/2 of the insulation out of the stud cavities around the room, and the room INSTANTLY felt MUCH better. So I know taking the insulation out will solve the issue. I’m going to keep the insulation hanging down like that for a while, with the fan running to mix up all the air, and the dehumidifier running (with the windows closed) to get that excess moisture out of the air, and see how that feels.
If it feels good I will pop the insulation back in and see what that does, hopefully without the vapor barrier there will not be a humidity buildup in that air gap. If it still feels good I will proceed to drywall, if it gets humid again then it seems basement walls with air gaps simply don’t work with insulation, I will trash it all and just drywall with no insulation.
So, after all that, my questions:
If there is an air gap between the foundation walls and the framing, is it correct to have a moisture barrier hanging over the walls tucked into the French Drain, then the air gap, then unfaced insulation in the framing?
If so, why is the stickiness feeling persisting with the (now unfaced) insulation in place? Do I just need to let the insulation air dry for a few days to release any trapped humidity? The insulation does not feel damp or wet at all (nor does the concrete wall or moisture barrier for that matter everything feels bone dry except my skin when I am down there)
If after a few days of drying I put the insulation back up and the room still feels fine, then would a Concrete Block → Moisture barrier → Air gap → unfaced insulation → drywall setup is OK?
If the unfaced insulaiotn does work and I need to put it back in place, I need something to help hold it in place and prevent it from falling into the 8 inch air gap. Previously the paper facing was stapled up an thats what help it in place. Can I use those metal insulation supports to keep the insulation from “falling into” the wall? Being 2x3 construction I don;t have the full surface area of a 2x4 to friction fit the insulation into.
If putting the unfaced insulation back up recreates the problem, WTF is going on?
With the insulation out of the framing the room feels fine again, if I cannot get any sort of insulation working, is it OK to just drywall over the framing and leave it uninsulated? I will be using the moisture resistant purple board drywall, and the room has no moisture problems. If I do that, should I keep or remove the poly moisture barrier?