Need advice on insulating walls
Looking for advice on insulating/treating interior walls in a split level kitchen where half of the wall is in-ground and the other above. Original walls were brick with concrete block, kraft/tar paper on interior side, 3/4″ furring strips topped with 3/4″ plaster. 2 exterior walls are now stripped from the interior to the concrete surface (was more practical to replace vs. patch drywall after rewiring/replumbing). We found no mildew and the room is comfortable – so one thought is to re-create what we had. The only difference would be that our new drywall is 1/2″ instead of 3/4″ plaster, and wood will be 1″ vs. 3/4″. Is there is insulation for the interior that is healthy, won’t cause mildew, and is not blown in? Should it be used on both the in-ground and above ground portions of the wall?
Thanks so much.
Katherine X
P.S. The house is located in Northern Virginia (Climate Zone 4).
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Replies
Katherine,
The below-grade portion of the wall (which, if I understand you correctly, is made of concrete blocks, also called CMUs) needs to be insulated like a basement wall. Here is a link to an article that explains what you need to know about insulating below-grade walls: How to Insulate a Basement Wall.
Before I can give you advice on insulating the above-grade portion of the wall, you need to describe its construction better. Is it just like the below-grade portion of the wall? In other words, is the wall made of concrete blocks from the floor to the ceiling? If so, you need to extend the same insulation you used on the below-grade portion, all the way up the wall.
-- Martin Holladay
Thank you so much Martin. Yes, the wall is concrete to the roof. Super helpful! Thanks.
Follow up questions if I may: Am I correct in that best practice/code involves attaching gypsum board directly to the concrete, followed by a layer of insulation, studs on top of that, followed by interior drywall? Or is the order rather concrete, insulation, studs, gypsum (i.e. interior drywall).
Are there good(ish) alternatives to place board insulation directly on the concrete in between studs/furring strips? We are limited in how much we can thicken the wall as we start to impede the entryway. Further, if possible, we want to integrate the new wall with an existing one if at all possible (1.5 inch thickness from concrete face to drywall on inside of the room).
If you have time:
Is it OK for wallboard and foam to touch the floor directly? We are about to level with a new layer of concrete and tile.
For fire blocking at the ceiling - is there a more full bodied fire-block than the stuff at big-boxes? (e.g. Great Stuff). It's hard to fill some of the bigger gaps with this.
Katherine,
Q. "Am I correct in that best practice/code involves attaching gypsum board directly to the concrete, followed by a layer of insulation, studs on top of that, followed by interior drywall?"
A. First of all, "gypsum board" is the same as "drywall." Other names for this product include Sheetrock (a brand name), plaster board, wallboard, and gypsum wall board (GWB).
Second, gypsum wall board should never be installed directly to concrete -- especially concrete that is below grade.
Q. "Is the order rather concrete, insulation, studs, gypsum (i.e. interior drywall)?"
A. That sounds better -- especially if the insulation consists of rigid foam or closed-cell spray foam. These details are explained in my article, How to Insulate a Basement Wall.
Q. "Are there good(ish) alternatives to place board insulation directly on the concrete in between studs/furring strips?"
A. Again, I urge you to read my article. You don't want the studs to be in contact with the below-grade concrete blocks. Instead, you want a continuous layer of rigid foam insulation or closed-cell spray foam between the concrete blocks and the studs. Moreover, you don't want to cut the rigid foam into narrow strips to insert between the studs. You want a continuous layer of rigid foam (installed with attention to airtightness).
Q. "Is it OK for wallboard and foam to touch the floor directly?"
A. The rigid foam can touch the concrete slab, but it's best if the gypsum wallboard is kept at least 1/2 inch above the slab.
Q. "For fire blocking at the ceiling - is there a more full bodied fire-block than the stuff at big-boxes (e.g. Great Stuff)?"
A. Great Stuff should not be used for fireblocking. I will post an image below that shows fireblocking details.
-- Martin Holladay
.
Martin, On that last question, Barbara may be referring to Great Stuff Fireblock.
Martin - Based on your extremely helpful instruction we will insulate a wall as recommended, but the second wall is another story. It will be too costly (reroute hydronic heat and destroy 2/3 of a perfectly good wall to get thickness right). Bottom line is I need to attach furring/studs to concrete block. Is there a good paint for the block? Another (not very green) option we're pondering is to use Tyvek between only the concrete and studs and leave the remaining concrete bare. All would be covered with drywall (regular or waterproof). Thanks in advance ,..
Katherine,
If you are trying to match the thickness of an existing wall, how many inches do you have to work with? Is the existing wall you are trying to match a 2x4 wall (3.5 inches thick), with the studs directly against the concrete blocks?
If so, you have room for 2.75 inches of continuous rigid foam, plus 3/4-inch furring strips.
If you have less room -- say, only 1 inch to the back of the drywall -- then you might consider 1/2" continuous foam and furring strips ripped from 1/2" plywood. Be creative.
-- Martin Holladay
Martin,
We have a total of 1.5 inches to work with which makes for a challenge. It appears 1 inch furring and 1/2 inch gypsum are minimally required. So at this point I'm looking for anything to help first with creating a good interface between cement and wood - and adding any insulation in the hole in between if it makes sense. Lastly, would 1/2 inch cement board be an insulation improvement over regular gypsum drywall?
Thanks so much.
Katherine X
Katherine,
Consider installing a continuous layer of 1/2-inch rigid foam, with 1/2-inch furring strips (ripped from 1/2-inch plywood). You should be able to fasten your 1/2-inch drywall to the 1/2-inch furring strips.
Q. "Would 1/2-inch cement board be an insulation improvement over regular gypsum drywall?"
A. No. But cement board is definitely more resistant to moisture than drywall, so it may be worth installing.
-- Martin Holladay
Martin,
Another complication. We have existing and will install several new receptacle boxes on the 1.5 inch-limited wall. I could not find anything on addressing this vis a vis the insulation. Are there any specific materials I should use around the existing receptacle box? The new boxes? I have 1.5 inches total to work with so the concrete has to be cut out in some spots and has already been cut out at existing boxes.
Also, any guidelines for design of the juncture between intact existing wall that has no insulation, and the new wall materials (insulation etc.) next to it?
Katherine X
Katherine,
If you are unsure about code requirements for electrical wiring, it is essential that you hire an electrician. Don't try to perform this work yourself.
I can't think of anything special to do at the seam where the insulated wall meets the uninsulated wall, except to say:
1. As usual, pay attention to airtightness.
2. It's quite possible that there will sometimes be condensation on the uninsulated wall -- although if you've managed to avoid condensation so far, you may be in luck.
-- Martin Holladay
In the interest of saving space, would it be good practice to adhere 1", 1-1/2" or 2" ridgid insulation to the concrete and then 2X4's laid flat against the ridgid insulation. The 2X4's could be shimed and anchored to the concrete if the walls are uneven. Then the space between the 2X4's could be filled in with 1-1/2" rigid insulation. The side of the 2X4's could be notched for wireing, with nail plates attached to the outside. If space is not critical, could the 2X4's being installed in the normal stud wall fashon, then infilled with a layer of 2" riged and an additional layer of 1-1/2" rigid, to give the highest R value?
Lloyd,
As long as the electrical cable is installed in such a way that it is recessed enough from the drywall (a) to meet code requirements and (b) to avoid damage from drywall screws, your plan will work. Steel protection plates will work, as long as your local electrical inspector approves of the way the cable is secured.
-- Martin Holladay
Martin,
Super appreciate your help in coming up with ideas. We are using licensed professionals for the job - so no worries there. We are still looking at all options considering the constraints/requirements.
-- Katherine X