It seems I will be using my basement's 12 inch poured concrete wall as the outer leaf (of a mostly 2-leaf system).
This will be the case with 2 walls of my studio-room.
The other 2 walls will be 'interior' walls (that is, they abut the rest of the basement).
They will need to be stud walls.
Now, the outer leaf of this stud wall will need to make an air-seal somehow with the the concrete wall.
How is this best done?
Should a stud rest directly on the concrete, or be some distance away?
Does there need to be anything special between the concrete and the stud?
Should only the outer-leaf sheet-rock touch the concrete (and be sealed with acoustic sealant)?
Also, the above floor will likely be used as part of the outer leaf (beefed with sheet-rock b/t joists, etc.).
How should the top plate of the outer-leaf create an air-seal with the the joists above, and how should a seal be created lengthwise between the joists (at the borders of the outer-leaf stud wall), and at the areas between the sill and joists?
I'm thinking that any 'hard' connection between the outer-leaf walls and outer-leaf joist floor above might compromise isolation by allowing potential flanking pathways....
Perhaps the attached diagram will illustrate my dilemma....
Note in the pic that the outside leaf perpendicular to the concrete wall (which abuts the rest of the basement outside of the studio-room) doesn't yet have any sheet-rock on it.
I'm worried about the areas at the points of the arrows....
I will be searching previous posts to see where this situation has been addresses already -- if someone can provide a link to that for me, that would be great...
thanx,
K
How to 'seal' outer-leaf stud wall to concrete wall ?
Originally posted at johnlsayers.com, topic 6055.
At best I might have a clue about the answer to this, at worst, you'll get a bump out of it:)
I was under the impression that you (and I) are supposed to actually connect wall studs to joists, but then use RC's to decouple the wall and ceiling surfaces to avoid flanking. This may be a rather poor understanding of the subject mind you, but I'm trying...
Very curious to hear more on this subject as I have the same dilemma, but 6 inch poured concrete walls. 12 inches should be a big help!
Good luck
Hi. Any response is quite welcome. Thanx. (about connecting studs to joists) Really? I was thinking that this would not be a good idea as it would provide a solid flanking pathway for sound. My walls are to be double-leaf, with separated plates and studs (perhaps also, even joists) for each leaf. Making any solid connections between leaves, or from a more isolated part to a closer, less isolated part, seems to be counterproductive. The biggest problem I have is with the outer leaf (the inner leaf should be 'easy' to keep from solidly connecting with any portion of the outer leaf); the walls of the outer leaf I wanted to have resting on the concrete floor, which is the furthest distance from the area I want to block sound from going. (The floor, will be simply the concrete (I'm not floating a floor, since there will be no 'impact' instruments on it, or really anywhere in the room)). Attaching the abutting stud wall to the concrete wall is not the 'scary' idea (I may HAVE to do it that way). But getting an air seal between the above floor joists, subfloor, and sill, IS the scary thing, because I feel making a solid connection IS where a compromise to isolation will occur.... I was under the impression that you (and I) are supposed to actually connect wall studs to joists, but then use RC's to decouple the wall and ceiling surfaces to avoid flanking. This may be a rather poor understanding of the subject mind you, but I'm trying...
I don't know why the foundation walls are so thick in the houses of my neighborhood, but they are (I measured) -- in fact, they are a bit OVER 12 inches. I have no worries, I feel, with isolation through any concrete sides in the basement (3 sides (out of 6) in the room will have concrete sides), yet I am planning on double-leafing the concrete walls by adding a single stud wall leaf in front of them (is this not a good idea? should I just leave the concrete as is?) I have plenty of room for double stud walls in the remaining 2 walls (interior side of the basment), so that shouldn't be an issue either. It's the CEILING treatment where the real worries lie. thanx, KVery curious to hear more on this subject as I have the same dilemma, but 6 inch poured concrete walls. 12 inches should be a big help! Good luck
This is a good question and I have the same situation.
Your outer leaf is only as good as the weakest link so the sill will be the weak point in your isolation since the concrete doesn't extend up to the first floor.
Without having build my inner walls, I can already tell that this is my weak point. Not sure if there's an easy solution.
i'm not sure why you are worried about solidly connecting different parts of your outer leaf together. if you are doing a true room within a room, with a 2 leaf ceiling, then it is the 2 leaves that need to be separate, not the different parts of the outer leaf.
you already have a direct connection in the outer leaf to the house above through the house's exterior walls, so how is isolating the interior parts of the outer leaf going to do anything. i would just focus on getting the outer leaf nice and airtight, don't worry about decoupling anything.
maybe if your whole room didn't touch the foundation anywhere it would help but i think you're wasting energy here. the more productive course would be to make a better inner leaf, and a better (larger) airgap.
and definitely beef up the sill area as Tom pointed out ...
also if you are doing a true decoupled 2 leaf system you don't need RC anywhere, it won't help if you are already decoupled.
and of course the gypsum doesn't need to directly touch at the seams, you would caulk all the corners so at least the gypsum isn't directly coupled, even if the frames are.
Guys,
This really isn't all that difficult - you just use iso-clips to attach your walls to the concrete foundation.
the outer wall of rooms that aren't adjacent to the foundation can attach directly to the structure - and then the inner wall near that attaches with an iso-clip.
See how easy that is?
I can post a few details if you want - but if you've ordered the book it's all in there........
Let me know..........
Rod
Yeah, 2 sides of the outer leaf will be the concrete wall itself... I was just thinking that connecting directly to the wood of the above floor joist would somehow be worse than any connection to the concrete. I somehow 'felt' that there would be less potential 'vibration' if the only part of the outer leaf connected to the above floor was only the above floor and joists (since the poured concrete is so thick). So, there would be no gain in, say, leaving a slight gap between the above floor joists and the top plates of the outer wall leaves and filling that gap with, say, acoustic sealant?you already have a direct connection in the outer leaf to the house above through the house's exterior walls, so how is isolating the interior parts of the outer leaf going to do anything. i would just focus on getting the outer leaf nice and airtight, don't worry about decoupling anything.
Are you saying that there is an effect of the gypsum not making contact, but not really any effect if the wood frame parts touch? Or is it that at least I would get some additional effect by separting the gypsum at the corners with acoustic sealant in between? I was never planning on using any RC in my project; I'm not sure if you are confusing me with someone else.... thanx, Kalso if you are doing a true decoupled 2 leaf system you don't need RC anywhere, it won't help if you are already decoupled. and of course the gypsum doesn't need to directly touch at the seams, you would caulk all the corners so at least the gypsum isn't directly coupled, even if the frames are.
1 - the 2 sides of the concrete wall do not create leafs - the concrete is one mass and therfore one leaf. 2. Your thinking is correct - you only want the deck assembly connected directly to the concrete - in that manner the outer leafs remain decoupled from the inner leafs. 3. As I noted in my post above - you can decouple this easily through the use of isolation clips attached to the concrete and wall - but at the top you have to install a fire stop - and this needs to be done carefully to maintain the decoupled leafs. This cannot be caulked with acoustic caulk - it has to be completed with rockwool and fire caulk.Yeah, 2 sides of the outer leaf will be the concrete wall itself... I was just thinking that connecting directly to the wood of the above floor joist would somehow be worse than any connection to the concrete. I somehow 'felt' that there would be less potential 'vibration' if the only part of the outer leaf connected to the above floor was only the above floor and joists (since the poured concrete is so thick). So, there would be no gain in, say, leaving a slight gap between the above floor joists and the top plates of the outer wall leaves and filling that gap with, say, acoustic sealant?
The gypsum touching would not compromise the decoupling of the structures - but the caulk is required to assure a sealing of the structure from the passage of air. Remember - where air can go - there goes sound. Sincerely, Rodsaying that there is an effect of the gypsum not making contact, but not really any effect if the wood frame parts touch? Or is it that at least I would get some additional effect by separting the gypsum at the corners with acoustic sealant in between?
I definitely see your logic ... but i'm just not sure it is worth the trouble. It is true that any sound that goes through your inner leaf to the outer leaf could travel up the outer leaf into your outer ceiling leaf which is your house floor. But I think that more sound will go through your inner ceiling leaf to your outer ceiling leaf and into your house. it's a more direct path. i mean, the outer leaf of the wall may be TOUCHING the upstairs floor, but the outer leaf of the ceiling IS the upstairs floor. that's a much better way to transmit the sound isn't it?? so yes, some sound will travel up to the house through the outer wall but since it will be less than the ceiling problem, it doesn't make sense to bother about it, since it will make no audible difference. Does this make sense? if you have 30 db of sound going into your house through the ceiling/floor, making the wall/ceiling construction a few db better won't give you ANY noticeable difference. it will sound exactly the same. i mean, even if you reduced the wall/ceiling problem to zero, you'd still have a 30db ceiling/floor problem wouldn't you? I mean, every little bit helps up to a point. But there is no difference in the performance between an equivalently constructed ceiling and a wall. so there is no point in making the wall perform better than the ceiling. unless you think that your ceiling/upstairs floor construction is somehow amazingly great, save for the littel problem of the outer leaf wall touching the ceiling. make sense? I think the RC comment was a response to someone else. as far as the caulking comment, that was just a general comment about how to do wall construction. sorry -- that was confusing. hope this helps. and if anyone wants to point out the flaws in my logic, please feel free. i'm here to learn too. :)I somehow 'felt' that there would be less potential 'vibration' if the only part of the outer leaf connected to the above floor was only the above floor and joists (since the poured concrete is so thick). So, there would be no gain in, say, leaving a slight gap between the above floor joists and the top plates of the outer wall leaves and filling that gap with, say, acoustic sealant?
Yes, I agree.... Actually my diagram doesn't show the stud wall (inner leaf) that will run parallel to the concrete wall. This stud wall will peak out at about an inch below the above floor joists. On top of the stud wall will rest the 'isolated' ceiling joists that run between the above floor joists. The area between the sill, above the concrete wall, and below the floor joists will likely be part of the dead air space between inner and outer leaves...... Not sure if I should block this off at some point for a very good reason: ** the floor joists actually seem to extend about 3 feet PAST the sill, and the above room occupies that area..... I may have great trouble getting sheet-rock there.... (I realize none of my earlier diagrams showed this aspect) thanx, KThis is a good question and I have the same situation. Your outer leaf is only as good as the weakest link so the sill will be the weak point in your isolation since the concrete doesn't extend up to the first floor. Without having build my inner walls, I can already tell that this is my weak point. Not sure if there's an easy solution.
That would mean that I can bolt the end stud of a perpendicular outer-leaf directly to the concrete wall? In other words, the walls interior to the foundation can have their outer-leaf stud frames firmly attached to the concrete foundation wall? Now, attaching the top plates directly to the joists above would put the stud lengths in compression every time the joists deflected with any varying live loads (or dead loads)... In the midspan of a joist, that could be up to half an inch or so... You can't mean that it's okay for the stud wall to be compressed along with the deflection of the joist...? After all, the outer-leaf stud walls in this situation are only partitions... Please explain why this would or would not be okay.... I'm gonna look again, but I didn't see any diagrams directly showing these things in Rod's book... thanx, KGuys, This really isn't all that difficult - you just use iso-clips to attach your walls to the concrete foundation. the outer wall of rooms that aren't adjacent to the foundation can attach directly to the structure - and then the inner wall near that attaches with an iso-clip. ...... Rod
Ooops. Well I do see on pages 48-49 where the outer stud wall is directly attached to the center beam of a basement.... So, then there would be no reason NOT to attached the outer-leaf frame to the concrete wall.... Looks like I may have been making this more complicated than it should have been (?).... NOW, what about the base plates on the concrete floor? Since I'm not floating a floor, both leaves' baseplates would be right on the concrete floor. I'm thinking I should/could isolate the inner-leaf bottom plate from the concrete floor? Or should both base plates be isolated from the floor? Neither? KGuys, ...I'm gonna look again, but I didn't see any diagrams directly showing these things in Rod's book...