Insulation detail
I have been progressing on my remodel. I need to button up the wall in the coming days. I had reached out to my local inspector who did not give me a ton of clarity. Wall profile is the following:
zone 6A with 2×4 framing, aluminium siding and 1×6 ship lap for sheathing. The WRB appears to be a shinny like paper. Following questions
I am versed on the detail to insulate the 2nd floor rim joist area, visible in the attached picture. However, I wanted to use 2 layers of 2″ XPS for an R-20 foamed in place. Any concern going this thick with the XPS
I have one exterior wall of a walk in shower that I was planning on using cut & cobble XPS the full depth of the stud cavity foamed in place. However, I am now considering placing a 2×2 on the face of the studs to increase the depth as I need to run my exhaust vent for the range in one of these stud cavities. By having more depth, I could place a 2′ piece of XPS against the sheathing, then run my ductwok in the cavity. This way I get some insulation in the cavity vs having the ductwork take up the depth. (it would have insulation sleeve around either way) In my zone is there a certain thickness of XPS I should not exceed?
Remaining portion of bathroom was going to install Kraft Faced FG and tape the seams. The existing insulation is old Kraft faced FG. Using unfaced with MemBrain would be my first choice, but this doesnt seem realstic, considering I only have some of the walls opened.
Last question not visible in this picture, is I have half wall opened in my kitchen. Here I have one wall the appears that the studs were doubled up with close to 7″ of depth. Their is a single layer of Kraft faced FG here. Would I simply remove the paper backing and then install an additional layer of kraft faced over the now unfaced FG? Does it matter that only half the wall would have close to full depth insulation, and the top half of the wall in which we did not remove the plaster have a single layer?
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Replies
MS,
The fiberglass batts that can be seen in the photo aren't installed very well. It would probably be worth it to remove the existing batts and to install new insulation materials.
Q. "For the rim joist, I wanted to use 2 layers of 2-inch XPS for an R-20 foamed in place. Any concern going this thick with the XPS?"
A. No. I would call R-20 the bare minimum.
Q. "I am now considering placing a 2x2 on the face of the studs to increase the depth as I need to run my exhaust vent for the range in one of these stud cavities. By having more depth, I could place a 2' piece of XPS against the sheathing, then run my ductwork in the cavity. This way I get some insulation in the cavity vs having the ductwork take up the depth. (it would have insulation sleeve around either way.) In my zone is there a certain thickness of XPS I should not exceed?"
A. No. Again (as with the rim joist question), it's hard to understand why you are worried about thick insulation. Thicker insulation is better than thin insulation. (I assume that your reference to "2' piece of XPS" was a typo. You probably mean 2-inch XPS, not 2-foot XPS.) So the plan to have R-10 insulation between your ductwork and the wall sheathing might be something that you are forced to do in a retrofit situation, but it's not "too much" insulation. It is too little insulation.
Q. "Remaining portion of bathroom was going to install Kraft Faced FG and tape the seams."
A. It's a waste of time to try to tape the seams of kraft facing. Kraft facing is not an air barrier. If you want an air barrier, install MemBrain or detail the drywall to be airtight.
Q. "I have a half wall opened in my kitchen. Here I have one wall the appears that the studs were doubled up with close to 7 inches of depth. Their is a single layer of Kraft faced FG here. Would I simply remove the paper backing and then install an additional layer of kraft faced over the now unfaced FG?"
A. You could do that. Or you could leave the existing kraft facing in place, and add more insulation on the interior side of the kraft facing. The existing kraft facing will do no harm.
Q. "Does it matter that only half the wall would have close to full depth insulation, and the top half of the wall in which we did not remove the plaster have a single layer?"
A. Well, in some sense it "matters" -- because walls with thin insulation don't perform as well from a thermal perspective as walls with thick insulation. But the thin insulation won't cause any moisture problems.
Martin. " No. Again (as with the rim joist question), it's hard to understand why you are worried about thick insulation. Thicker insulation is better than thin insulation"
A. I was more curious about the perm rating of having that much foam insulation in my Zone 6A vs any concern regarding having too thick insulation. Obviously this concern was not warranted based on your response.
Sounds like detailing with ADA for the air barrier is my best bet. I did want to ask after watching one of the instructional videos hosted by Myron Ferguson whether it makes sense to try to seal these seams in my 1x6 ship lap sheathing, The gaps are between .125 and .25" wide. I suppose caulk or even more efficient may to use the new Great Stuff Foam gun I purchased and hit these seams with the canned foam? Worth the effort?
The bathroom is on the second floor, which is in the conditioned envelope. Is it worth insulating the floor in the bathroom for sound dampening purposes? While I am sure, the answer will be its up to me, I am wondering how common it is? Perhaps the interior walls that surround the shower, would be a better area to concentrate on? Limiting noise of what happens in the bathroom would be beneficial for everyone, at least in my house!
MS,
Q. "I did want to ask whether it makes sense to try to seal these seams in my 1x6 ship lap sheathing."
A. If you want an exterior air barrier for this type of wall, you would have to use the cut-and-cobble approach or the flash-and-batt approach. Either of those approaches would result in a better performing wall than just using fiberglass batts.
For more information on cut-and-cobble, see Cut-and-Cobble Insulation.
For more information on flash-and-batt, see Flash-and-Batt Insulation.
Q. "Is it worth insulating the floor in the bathroom for sound dampening purposes? While I am sure the answer will be, 'It's up to me,' I am wondering how common it is."
A. It's up to you. And insulating bathrooms for sound reduction purposes is common.
I wanted to follow up on an observation regarding my question pertaining to the "seams" in the 1x6 shiplap sheathing. To be clear the above picture is looking at the wall from the interior. When I removed the old Kraft faced FG. I noticed on several of the batts, the FG appeared dirty with horizontal line seemingly matching up to the seams on the wall. This I would presume to be a tell tale sign the wall was prone to leaking air and the seams were the likely spot.
While I understand the approach you advocated above if I want an exterior air barrier, is their any reason not to run a quick bead of foam in these seems while I have the walls the opened up on the interior? The foam gun makes quick work of that and perhaps although minimal, would seem to address some of the most susceptible areas.
MS,
Q. "Is their any reason not to run a quick bead of foam in these seems while I have the walls the opened up on the interior?"
A. No.
If using rigid foam for the exterior air barrier it's better to use a cut'n'cobble thick enough to meet TABLE R702.7.1 for the depth of fiber insulation (scroll about 1/4 of the way down to find the table : http://premiumaccess.iccsafe.org/document/code/343/5658090 ) which for zone 6A would be a bit over R2 of foam for every inch of fiber depth.
Do not use the labeled R value of XPS, but rather it's fully depleted R (after it's blowing agent has dissipated), which is R4.2/inch @ 75F mean temp, or R4.5/inch @ 40F mean temp, but not R5/inch.
eg: Assuming those are full-dimension 2x4s you have 4.0" of total space. Installing half inch XPS would leave 3.5" of space, a perfect depth for standard 2x4 batts but R2 x 3.5" is R7, and a half inch of fully depleted XPS is only good for R2.25@ 40F, not even close. With 1" XPS you'd have 3" of fiber depth, needing R6, but would only have R4.5. You'd be good with 1.5" XPS (R6.75 @ 40F) and 2.5" of fiber that only needs about R5. So if 2" is what you have, it's "good enough".
If the seams of the ship lap are dirty the caulk may not stick everywhere, but it doesn't hurt. It won't make the sheathing into a true air barrier, but it'll be a heluva good air-retarder, which is all to the good.