Wall Intersections – Thermal Break?
2001 gut reno – CZ 3A/4A
Can someone please help me figure out what to tell my contractor to do for interior wall intersections like the ones in the attached photos? We are doing Rockwool in the stud bays, but I’m at a loss for what to do in these areas.
Would not insulating create a thermal break here and lead to potential issues? Or is it ok to just re-caulk / foam the seams and call it a day (like it was previously done when the home was built)?
Or do we need bother insulating/sealing those corner seams at all?
For extra context, here’s our assembly:
Hardie, Benjamin Obdyke Slicker Max rain screen, Tyvek commercial wrap, OSB w/ taped seams using Siga Wigluv (Fentrim at slab)… Rockwool and drywall to come soon
Our goal was to make the home more air tight, not perfectly air tight.
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Replies
Fill the voids with canned spray foam and call it a day. You can even use high expansion foam if you'd like in this case, but regular window and door works as well (you'll just use more of it).
It's otherwise not the end of the world if you don't get this detail perfect, as you're in a pretty mild climate and have taped the seams on the sheathing outside.
Jamie
I'm going to assume here that you want to insulate the interior void between the studs at that T junction? There is no problem insulating in there, and you SHOULD insulate in there to avoid a cold spot. If there is no way to get in there with the batts you're planning to use, then injection foam is probably your best option. Note that you might be able to just pop one of the studs out and then toe nail it back in after insulating.
Bill
Correct, that's what I'm referring to. Thank you! A few follow-up questions:
1. Does injection foam come in closed cell & open cell options? If so, which would you recommend for my climate zone (GA - 3A/4A line)?
2. What about corner junctions like this pic (attached)? Do you recommend the same method for insulating, or are these treated differently?
3. If we taped the exterior OSB seams with Siga Wigluv, do we also need to caulk the junction seams like it was done previously (the white caulk in the pictures)?
Appreciate the help!
1- The two part injection stuff is usually closed cell as far as I know. Your install contractor can tell you for sure. I will sometimes used canned foam in small spaces like this, and that stuff, while it claims to be "closed cell", is really a bit of a mix of both.
2- Sometimes those corners have an extra stud or two in them, so insulation doesn't always fit. You'd probably need to insulate these from the exterior. Sometimes 1.5" thick rigid foam is handy here, because it can fit into a stud-size space. I would try to insulate ALL areas of the exterior wall as much as possible.
3- I like to caulk too, although I prefer to put the bead of sealant between the faces of things and not on the edge, but that's not usually an option with renovation work. With air barriers, it's best to have more than one for reedundancy. Tape AND sealant helps to make sure you have a good air barrier in case either isn't 100%.
Bill
Thank you! On the caulk & foam topic... We were unable to air seal the top plate from the exterior due to a full hip roof, so we plan to seal the tops of the stud bays (horizontal seam and about 6" down on each side of vertical seams). We were initially thinking canned spray foam, but now I'm rethinking. Do you think caulk would work better in this instance? Spray foam is definitely quicker/easier, but we want the best outcome possible, not just the easiest route. We have plenty of Prosoco AirDam left over from the windows if that would work for this. Or does it really matter what we use here?
Our contractor is ok with removing studs on the T junctions so we can get batt insulation behind those wall intersections. He's not a big fan of doing that in the corners (and there were also a couple T junctions that are load bearing that he's unsure about). The exterior is done, so adding insulation there isn't an option. A few follow-up questions:
1. He might be able to get some canned foam in there - is the high expansion or low expansion better in these areas?
2. What is the risk we run if we aren't able to fully fill those areas or if there are some we aren't able to get to at all?
3. If it's better to have redundancy with the air sealing, what should we do if we weren't able to tape the top plates from the exterior? We ran some caulk in the tops of the stud bays and down about 6". Should we add tape on top of that (might be difficult with some nails in those areas)?
Note that there are different ways to frame a corner. I suggest you look up "advanced framing techniques" to get some ideas. A strip of 1.5" foam can be inserted into a gap left in some of the advanced framing style corners to get a bit better insulation in those areas. Some details allow batts to fit in more of the corner. See which way your GC is more comfortable with.
Bill
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Sounds like these options would require opening up that corner or removing studs in order to redo the corner. He's not comfortable with removing studs that are attached to our OSB sheathing already since it's a reno. He wants to fill those cavities with spray foam, specifically Loctite fire-rated gaps & cracks foam. Would that be a suitable solution?
I don't see any problem using canned foam to fill any gaps. I've done that myself many times.
Bill
He's using it to fill the entire void in the corners, not just small gaps. Is that ok?
Will the fire-rated canned foam provide enough R value for those corners?
You'd probably want to use the canned foam that is made for "large gaps" here. You'll need to inject it in multiple locations spaced along the gap to get good fill. Don't try to inject it all in one end -- that won't work.
You don't need the fire rating in this location. You need the fire rating for penetrations through vertical blocking and certain penetrations between spaces horizontally. Your application shouldn't be subject to the fire block requirements.
Bill
Any specific products you'd recommend for the best outcome?
It looks like he already did one corner with the loctite fire foam before asking if that's what we wanted to go with. Would you recommend we try to remove and redo it?
I wouldn't worry about it if he already used the "fire foam". I like Loctite's TiteFoam, which I think is GE branded now (but still made by Henkel). They make a "big gap" version and it works well. I like this stuff because it makes a denser and stronger foam than others I've tried, so I like to use it in places I want something tougher than the regular stuff. The tradoff is the TiteFoam product costs more.
Dow also makes a big gap version of their Great Stuff product that will work, and is a bit cheaper.
Bill
I know that redundancy with the air barriers (tape on exterior, caulk on interior) is helpful in case one or the other isn't 100%, but I'm confused about why this couldn't also be a bad thing from a dryability standpoint.
For example, if the corner seams are taped on the exterior with Siga Fentrim, and the interior corner seams are caulked, what happens if moisture makes its way into the cavity? Wouldn't having one side "open" allow for proper drying?
tjones,
As Martin and others have so aptly put it: Buildings don't need to breath.
Apart from dedicated vent spaces like rain-screens and roof vent channels, moisture gets removed through diffusion, not by air movement. That's why we use high-perm materials on the side of any assembly we want it to dry though.
As well as reducing the effectiveness of the cavity insulation, air-leakage is likely to introduce more moisture that it removes.
If the exterior corner is taped, and the interior will be drywalled (interior air barrier), do we really need yet another air seal (caulking the vertical seams of the corner studs)?
tjones,
No, I don't think you do.
Ok, great! I'm trying to evaluate options for getting insulation into those corners. Once we figure that out, we will instruct our our insulation guys to not seal those vertical corner seams. Thanks!
@tjones1014 - the way high performance builders deal with this detail is to use advanced framing techniques. In your case, at this point you need a solution that minimizes trips for the specialized trades (ie you do NOT want a stud removed so you can insulate and then require the framer to come back and reinstall it; you want only one framer return trip) and maximizes the probability you will get a good job. You are correct to be concerned about this as even in GA lack of insulation in these locations will give you very cold spots. Absolutely get this addressed.
Here is a link that shows a standard framed corner and then an advanced framing corner from the Building America website: https://basc.pnnl.gov/resource-guides/advanced-framing-insulated-corners#edit-group-description
If your contractor is willing to remove what is the upper right stud in the traditional diagram, it can immediately be reinstalled in the location shown below it. This will then allow the insulation sub to install insulation into the corner.
Similarly, here is a link to the advanced framing detail to use when an interior wall intersects an exterior wall, so that you can insulate. This shows the traditional detail, such as you have, first then the advance which allows insulation.. https://basc.pnnl.gov/resource-guides/advanced-framing-insulated-interiorexterior-wall-intersections#edit-group-description
In this case, implementing the advanced framing detail may be impractical, because it would require moving two studs to which sheathing is already attached, and which may be at the far edge holding the sheathing. If your contractor is willing, perhaps ask him to have the framers turn one exterior wall stud 90 degrees. It could then still support the sheathing, and it would create access for the insulator to properly insulate.
All the above said, the insulators will need to cut the rockwool insulation to the resulting non conventional cavity size. You will need to watch closely to ensure they do this properly, but I think it is easier to do it properly with rockwool than with fiberglass batts, so you have that going for you.
For the corners - If my contractor were to remove the stud in the upper right of the traditional diagram like you were talking about, that would involve cutting through the nails that attach the OSB and other exterior items (WRB, ran screen, siding) to the stud. Would that affect the stability of that corner? Both from a structural standpoint and when considering what all might be nailed into it.
And I'm assuming when it's reattached, we would just nail it into the other corner studs and not bother with attaching it back to the OSB. Is that correct?
So that we are all looking at the same diagram, I've downloaded and attached the Building America Advanced Framing corner details.
The stud in the upper right of the conventional image is inboard of the corner, so technically it should not be the primary location at which the sheathing is attached. You could figure out if there are fasteners through it by attempting to slide a piece of paper or extremely thin plastic or metal between the outside face of the stud and the sheathing. If you don't hit anything, there should be no issue relocating it. You would relocate it to the location shown on the Advanced Framing image; it is needed at that location so that there is something onto which the interior gypsum can be fastened. Some also believe it is needed to strengthen the corner.
All of the corner studs I tested with paper and/or a metal spatula either had fasteners through them, or they were so tight to the OSB that I couldn't slide anything back there to test. Suggestions?
tjones,
I’d go back to the advice from Jberks and Bill in the first two posts. Drill a few holes, fill with canned foam, and call it a day. It’s simply not worth the effort involved considering how small the voids are.
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Yes. Follow @Malcom Taylor's advice in post #24...
Is putting rigid foam around the interior of the corners an option? Or does the insulation have to be in that void to be effective? I'm chemically sensitive and trying to avoid spray foam if at all possible.
Is removing one of those corners studs a bad idea if there are fasteners in it?
Is blowing some rockwool granulate into those cavities possible?
Sorry to be complicated! My contractor still doesn't understand why we need to insulate those corners and just wants to leave them as-is. He's been no help in finding creative solutions here.
Or I found this note from Martin from 2018 regarding someone's garage. Is this acceptable? And if so, would we just fur it back out once it's insulated?
"You can use a Sawzall to remove half of one stud -- ripping it from 3.5 inches to 1.75 inches wide -- so you can access the void and stuff it with fiberglass or mineral wool."
https://www.greenbuildingadvisor.com/question/insulating-conventional-corner
You have competing issues here
- If you remove 1/2 the stud, I suspect your contractor (whom you have indicated does not even think the corner needs insulation) will object. You run the risk of the contractor refusing to warrant the framing and of alienating the contractor.
- You are concerned about environmental issues
The environmental issues of canned spray foam are likely FAR less than the possible issues with issues with site mixed two part open or closed cell spray foam; the issues with that are often related to how it is mixed and applied, and those are not issues with canned spray foam. Also, it is unlikely you can stop spray foam from being sprayed - your builder and the builders subs will undoubetly use canned spray foam all over - it may already have been used. You may consider that there will be considerable time between the time the spraying of the canned spray foam and your occupancy, so plenty of time for whatever there is to dissapate.
The second, larger issue you may need to address is that it seems you want a reasonably performing home rather than what is "standard." If your contractor does not even understand why the corners should be insulated (and is obviously not using advanced framing techniques, which come at no additional cost, to acheive better performance), your contractor and you are not on the same page.
Others on this site could help, but I wonder if a literal reading of the code requires these corners to be insulated. Overall, your concern should be how tight your house is. I hope that your contract calles for a specific level of air tightness, and gives you the right to hire YOUR OWN independent consultant to test for air tightness, and has proper terms to require your contractor to fund continuing to seal (with aeroseal or other) until the contractor meets the contractually specified air tightness.
Your other option for the corners is to ask the insulator if they can figure out a way to dense pack some cellulose into the corners via small holes. I don't even know if this is possible - ie if the insulator has a smaller end of the dense pack machine - if you drill the size hole they usually drill for dense pack it is the size of the entire stud and the stud will no longer be doing much...
Our contractor said he's willing to do whatever we decide, so I'm looking for guidance on if cutting the studs in half is even a good idea (or if there is another better solution). With this being a 2001 reno, we didn't have the option to select framing details like this beforehand. We are doing the best with the cards we've been dealt. That's all we can do.
We understand that some foam will be used. We aren't trying to eliminate all spray foam entirely, but with most of the corners being in bedrooms, we would like to avoid it if possible. Managing chemical sensitivities is all about limiting exposure, and we especially want to limit it in rooms our family will be sleeping in (where almost all the corners are). Additionally, I have seen firsthand how canned spray foam can separate and crack over time, and I'm not a fan of risking water/condensation getting trapped in the corner cavities if we ever have water issues in those areas. We have had similar issues in a past home, so we know it's possible.
Our contractor is aware of our expectations. He's just used to the standard way of doing things. Again, he's willing to approach things in whatever way we wish, and we have a great relationship with him, so that isn't a worry. We just need guidance and someone to help us come up with a creative solution.
Yes, we are taking/have taken measures to ensure our home is more air tight and have people on our team to ensure that.