Insulating basement
My name is Paul.
I have a newer home with poured basement walls. Put plastic in different areas of basement and no moisture appeared.
No moisture in concrete basement walls.
1)Will building a stud wall against the concrete wall and using Batts cause moisture to form even yhough I didn’t get any moisture on the test?
2) if you think it will create moisture, then can I just build the wall about an inch away and use a fabric to keep the Batts from falling in against the concrete wall?
I also thought about just gluing like 1/4 inch Styrofoam against the back of yhe studed wall to keep the Batts from falling against yhe concrete. Or just maybe standing up pieces of Styrofoam 1/4 inch thick between the stud wall and concrete to keeps the Batts off the concrete.
3) do I really need to use 1 to 2 inch Styrofoam and glue it to yhe concrete wall before I stud a wall. I do t have a moisture issue unless you think I will create one by building the studed wall.
Just seems like a lot when I don’t need it.
2 inch foam sealed and then a stud wall
Around the room takes like a foot of space away.
I would just like to stud a wall and put Batts up. But I’m afraid if there is moisture, I don’t want the Batts to fall in against yhe wall and create a mold issue.
4) If I need to use a rigid foam, what is the minimum thickness I can get away with.
It’s not for insulation at yhis point.
It’s for a moisture barrier. Will moisture permeate thru a quarter inch of Styrofoam.
Do I need a half, one inch or more to seal as a vapor barrier.
I just feel like if I don’t use foam sealed on the concrete wall, it won’t create moisture and it allows air to move and get to the concrete.
Your help would be greatly appreciated. Just want to get this step right.
Thank you
Paul
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Replies
https://www.insofast.com/
Skip the wood stud wall ...
👍
1 - What's going to condense is the thermal bridge. So in your case - the stud, not the batt. If you install the studs with an air space between them and the concrete wall - I wouldn't expect any condensation issues.
2 - I wouldn't worry about the batts touching the concrete - but placing a continuous rigid foam layer between the concrete and your wall assembly is a far better method.
3 - See #2
4 - I'd review the prescriptive energy code for your area on a conditioned basement wall for an R-value. EPS will be your best option for moisture while poly-iso will provide the most R-value per inch.
Another option to consider would be to spray foam your basement walls - either before or after you fur it out for your finished wall cladding. This gives you an excellent moisture and air barrier - and depending on your home construction - potentially a way to seal your rim board if it isn't already.
Thank you
jaywbee,
Neither the stud or the batt insulation are what you are worried about. The first condensing surface of interest (as Joe Lstiburek terms it) is the inside face of the concrete. Whether the batts touch it or not makes no difference to the concrete attracting moisture.
You can make your life simpler by knocking out a couple of strategic studs to let you get the foam behind.
1.5" is the target, if in areas it is only 1" that is fine. Important part is you want the foam layer air tight, so make sure to tape all the seams and run a bead of caulk between the foundation and the top and the bottom of the foam.
The one you don't want is no foam and batts, that is a risky assembly.
If you are using polyiso and there could be a chance of basement flooding, then it makes sense to keep it a couple of inches off the ground. XPS/EPS/GPS/NXG can all be run to the ground.
After insulating the walls, the most important detail for a comfortable basement is air sealing your rim joists. Stuffing batts into there won't do anything except filter the air leaks, you need to seal this area up with either spray foam or rigid insulation sealed in place with canned foam.
Thank you.
Paul68,
As Akos said: using only permeable insulation (batts) is asking for moisture problems. It isn't the moisture from the concrete you are worried about, it's the moist inside air making its way through the insulation and condensing on the inside face of the foundation walls. That's what you need the foam for. The air can't move through it.
Had the same dilemma didn’t want to lose a foot of space. I glued, taped, and sealed 1inch of rigid foam against the wall, turned a 1x4 on the flat and attached to wall. That’s a 2in wall, that’s 3in even if I had 2 inch of rigid foam. Basically it’s not thicker than a 2x4 wall and no worry about batts touching concrete. Much safer and if you are really want to pack more insulation you can place more rigid foam between the studs although I didn’t think it was necessary. Room is comfortable most of the year, a little cold in the winter but a heater works right away.