Basement drywall repair / vapor barrier question
June 16, 2019 2:50 PM Subscribe
I am patching a hole in the drywall in the basement; should I also fix the vapor barrier behind the wall? Or nah?
So, the moisture problem on my basement wall seemed to be getting worse. I used a drywall saw to cut out the drywall that seemed moist/damp and found a small amount of moisture in the wall cavity and insulation behind the drywall. It seems like water had infiltrated through the exterior cement basement wall, making the cement clammy to the touch (like a "seep" through the cement, not a running leak). To fix the seep, I ended up getting my gutters cleaned and fixing the grade that runs against the exterior wall, which I think has stopped the moisture. The cement looks very dry now, even though we have had more rain.
But, now I have a gap in my drywall (roughly 1 foot square) and I pulled out the insulation that was behind that gap because it was damp/musty. There was also a plastic sheet between the drywall and the insulation, which I think was part of a vapor barrier system. It looked a lot like this. I accidentally cut the plastic sheet with my drywall saw when I cut the wall, but, also, some of the insulation was wet so I ended up pulling out more insulation and plastic beyond what I had accidentally cut. Basically, the whole 1'x1' area now has nothing between where the drywall will be and the exterior cement. The vapor barrier and insulation is cut open all around this hole.
Here's the question: do I need to do anything to fix the insulation and vapor barrier before I patch the drywall? Is it bad if I just slap a drywall patch over it and leave the vapor barrier/insulation alone? Part of my thinking is that, if I get "seeping" again, I'd prefer not to have a bunch of wet insulation in there again. But I don't really understand what the vapor barrier is supposed to be doing - and googling leads to a bunch of controversy about whether you need a vapor barrier or not, with some people saying that a vapor barrier just creates dampness behind the drywall.
Any other suggestions for things I should do before I seal it up? I have half a mind to put some kind of desiccant/moisture-remover behind the wall (like Oil-Dri stuff) on the chance that a little bit of moisture gets in again, but there is probably a good reason people don't do that.
So, the moisture problem on my basement wall seemed to be getting worse. I used a drywall saw to cut out the drywall that seemed moist/damp and found a small amount of moisture in the wall cavity and insulation behind the drywall. It seems like water had infiltrated through the exterior cement basement wall, making the cement clammy to the touch (like a "seep" through the cement, not a running leak). To fix the seep, I ended up getting my gutters cleaned and fixing the grade that runs against the exterior wall, which I think has stopped the moisture. The cement looks very dry now, even though we have had more rain.
But, now I have a gap in my drywall (roughly 1 foot square) and I pulled out the insulation that was behind that gap because it was damp/musty. There was also a plastic sheet between the drywall and the insulation, which I think was part of a vapor barrier system. It looked a lot like this. I accidentally cut the plastic sheet with my drywall saw when I cut the wall, but, also, some of the insulation was wet so I ended up pulling out more insulation and plastic beyond what I had accidentally cut. Basically, the whole 1'x1' area now has nothing between where the drywall will be and the exterior cement. The vapor barrier and insulation is cut open all around this hole.
Here's the question: do I need to do anything to fix the insulation and vapor barrier before I patch the drywall? Is it bad if I just slap a drywall patch over it and leave the vapor barrier/insulation alone? Part of my thinking is that, if I get "seeping" again, I'd prefer not to have a bunch of wet insulation in there again. But I don't really understand what the vapor barrier is supposed to be doing - and googling leads to a bunch of controversy about whether you need a vapor barrier or not, with some people saying that a vapor barrier just creates dampness behind the drywall.
Any other suggestions for things I should do before I seal it up? I have half a mind to put some kind of desiccant/moisture-remover behind the wall (like Oil-Dri stuff) on the chance that a little bit of moisture gets in again, but there is probably a good reason people don't do that.
Vapor barriers are indeed required by code.
However- think how it supposed to work. We humans respire, we sweat, we wash, we cook, bathe. We generate water vapor. We make it more humid inside than out (if you don't live in Florida*)
The water vapor wants to travel from somewhere where there is more to somewhere where there is less. Vapor pressure.
On an above grade wall, if the vapor could move freely into the wall, it would condense somewhere in your insulation during the cold moths. Not good.
The questions you have to ask yourself are:
What is the usual relative humidity in my basement?
Is the temperature of the concrete going to be below dew point for that amount of moisture in the air? This is the concrete at any point where the vapor can reach.
If yes, then a vapor barrier is advised.
Latex paint on gypsum board is a fine vapor barrier, if you seal around the outlets etc that penetrate it.
*The code actually recognizes the difference in S Florida. There, the vapor barrier goes on the outside face of the insulation.
posted by rudd135 at 4:49 PM on June 16, 2019 [2 favorites]
However- think how it supposed to work. We humans respire, we sweat, we wash, we cook, bathe. We generate water vapor. We make it more humid inside than out (if you don't live in Florida*)
The water vapor wants to travel from somewhere where there is more to somewhere where there is less. Vapor pressure.
On an above grade wall, if the vapor could move freely into the wall, it would condense somewhere in your insulation during the cold moths. Not good.
The questions you have to ask yourself are:
What is the usual relative humidity in my basement?
Is the temperature of the concrete going to be below dew point for that amount of moisture in the air? This is the concrete at any point where the vapor can reach.
If yes, then a vapor barrier is advised.
Latex paint on gypsum board is a fine vapor barrier, if you seal around the outlets etc that penetrate it.
*The code actually recognizes the difference in S Florida. There, the vapor barrier goes on the outside face of the insulation.
posted by rudd135 at 4:49 PM on June 16, 2019 [2 favorites]
As someone who does own a basement in a very humid region, I'm gradually getting rid of all the drywall down there - the fact that masonry breathes is a distinct advantage to my mind, and the vapor barrier is really just a way of delaying the inevitable.
You need to repair the vapor barrier if you plan to keep having drywall and insulation. But I'd very much consider whether there may be seepage/moisture beyond the single square foot you found.
posted by aspersioncast at 9:46 PM on June 16, 2019
You need to repair the vapor barrier if you plan to keep having drywall and insulation. But I'd very much consider whether there may be seepage/moisture beyond the single square foot you found.
posted by aspersioncast at 9:46 PM on June 16, 2019
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Short answer (from someone who doesn't own a basement) is yes, you need to fix those things, they are there for a reason (and probably required by the building code?). You also need to do whatever else is required to keep your timber wall dry, because wet timber rots (assuming yours is like the photo).
I presume you have done the earthworks to keep the surface water away from your wall?
posted by GeeEmm at 4:00 PM on June 16, 2019 [1 favorite]