Submitted by slickwrick21 t3_1152jdi in DIY
Live in GA, house built in 2010. Just insulated my basement (getting HVAC installed). There is “black tar” on the outside of the wall below ground. This batten is up against the concrete, do i need a vapor barrier or tape this? Can i just leave it and throw on sheetrock? walls with r-13 insulation
No vapor barrier for below grade concrete walls: water vapor from soil permeates through the concrete and will get trapped in the wall. From buildingscience.com: “Constructing frame walls, insulating the resulting cavity and covering with an interior plastic vapor barrier is common and often leads to odor, mold, decay and corrosion problems.”
and that includes paper backed insulation.
Polyurethane sheeting is a typical vapor barrier that contractors use to prevent moisture from penetrating the walls of a basement. The material is stapled to the frame of a basement wall before it is finished with plaster or drywall. A vapor barrier is also helpful to keeping a basement insulated and warm. * https://www.hgtv.com/design/remodel/interior-remodel/how-to-install-a-basement-vapor-barrier
They did this in my house, and it caused mold and rot. Moisture will get in regardless of the outside seal, and while the vapor barrier will keep moisture in the wall and out of your basement, it’ll also slowly rot away the framing stuck between the vapor barrier and the wall below grade. It took maybe 20 years, but all the framing where we found a vapor barrier was severely degraded, and framing where there was no barrier was in amazing shape.
If you’re happy to let it rot to have a little less moisture come in, it works, but the lifetime of the framing will be cut short.
I’d advise either sealing with foam directly against the concrete, or skip the moisture barrier. As long as it’s well air sealed, vapor will slowly escape, allowing everything to dry.
I don't know your build or what happened, but generally speaking, the vapor barrier is intended to keep moisture out of the wall, not out of the room. In fact it should keep it in the room.
That being said, concrete does sweat, so foam board instead of fiberglass directly on the wall is still likely better and potentially where your moisture came from.
If op wants to use a vapor barrier in the basement they should be using a smart barrier.
or shellac based primer on the drywall - in general.... it acts as a vapour barrier.
but I wouldn't use it in a basement without a LOT of ventilation.
That looks like paper face to me, which means the vapor barrier is built in. However, it should have extra flaps on the side that you staple to the studs to close up the vapor barrier (otherwise the studs become a point of ingress for moisture into the insulation)
Yeah should be flush with the beams and tacked for a complete seal
That paper backing is actually a vapor barrier (worked for an insulation company in the northwest) but I would suggest looking into coding for a basement for higher humidity areas
I was thinking this too. If its a basement, wouldn’t they not want a vapour barrier? Spray foam or rigid foam insulation directly onto the concrete is a better option? I guess depends where you live. Im in Canada where the ground freezes for 6 months out of the year.
Yeah I know foam board is normally recommended but in some cases I have seen Kraft batts used in basements depending on the ability to keep moisture and humidity under control
Do i need to staple it to the wood or can i leave it as is?
Staple it. It will take 60 minutes top.
Yes the paper should be stapled to the wood should have a an overlap on one side also might want to try to fix the compression in yours bats so get your actual r value
if you want to drywall the basement you want to remove those batts and replace them with unfaced batts, rockwool or XPS. Rockwool is moisture resistant.
DONT staple it, (if you can) … remove the paper prior to sheetrock. You do not want an additional vapor barrier holding in humidity.
If you remove that vapor barrier that's glued to the batts you damage the batt as well vapor barrier should be secured if op staples this vapor barrier then they do not need a poly vapor barrier as well again I still suggest that local coding is checked but manufacturer says to secure the vapor barrier that is on the batt not to be just removed or else the r13 value that is up is no longer r13
The entire wall (wood, insulation etc) is supposed to wrapped from the top down under the 2x4s then back up to the top of the interior of the wall, so 2 layers of vapor barrier in a "U" shape. Putting a vapor barrier only on the inside will keep moisture inside the wall if it ever gets in and will cause mold. This was not done correctly.
No no no no. Never fiberglass in a basement. Never. Closed cell foam. Spray or sealed sheets.
This is probably the best recommendation, honestly. I've also heard of people doing foam board against the concrete and then batting over that.
I also second the other recommendation to see if there's code specific to your area since it is likely high moisture/humidity
The problem is that concrete is a huge thermal mass. Any change in humidity in the conditioned space will cause a surface effect on the concrete and adversely affect the fiberglass insulation and wood framing.
I did that, but I used rockwool which is moisture resistant.
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If those batts are just friction fit I would pull them out and fit rigid foam against the foundation and spray foam any seams and then if you want to you could put the batts back up followed by drywall. No need for poly. I recommend looking at fine homebuilding a website for more information
https://www.finehomebuilding.com/project-guides/insulation/build-a-risk-free-finished-basements
I’ll second this. In my 70’s home, had the benefit of having bare walls to start. I put up 2” poly iso board against the block wall, sealed gaps with spray foam and insulation tape, then framed in front of that and put in r-15. There is also a French drain installed. My basement is the warmest dryest part of the house now.
You do not want a vapor barrier on the inside of your. basement walls. The paper backing on the insulation is a vapor barrier. You should replace that insulation OR don't drywall over it.
https://buildingadvisor.com/materials/foundations-sitework/basement-insulation/
It's probably not code to leave it exposed without drywall, but i agree that switching to a water resistant insulation is gonna be better in the long run.
Would you rather save a tiny but of time and effort now, or spend a lot of money fixing mold issues later?
You need barrier. Absolutely .
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Black sealing caulking as well.
Do you absolutely need drywall? I am also in GA and I just primed and painted the concrete walls in my basement. The dirt and poured concrete insulates far better than the rest of the house and I have no moisture problems. I see you have already framed out for drywall, but if taking it out and having concrete "industrial chic" walls is ok, then it's a possible solution
The faced insulation acts as a vapor barrier!! But if you had used unfaced they do have a smart barrier that allows to breath when moister is present and when not it acts as a solid. Pretty cool stuff.
If you don't put up vapor barrier, you'll always be thinking about it. One chance to do it and the time is now
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I'm sorry but you are incorrect.
https://buildingadvisor.com/materials/foundations-sitework/basement-insulation/
You don't want a double barrier. If the outside of the foundation is tarred you can finish the interior to your liking.
(Not an expert)
Cinderbolt77 t1_j8zfbpl wrote
Pretty sure you need barrier, regardless of tar on outside, you are going to have condensation on the inside.