Best insulation method for outside walls? - AVS Forum
View Poll Results: Insulation method you prefer?
Foamboard, air gap, pink fiberglass 13 68.42%
Air gap, pink fiberglass 1 5.26%
Some other solution 5 26.32%
Multiple Choice Poll. Voters: 19. You may not vote on this poll

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post #1 of 46 Old 07-16-2013, 07:07 AM - Thread Starter
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I'm going to be moving to a new house (new construction) shortly, and hopefully starting a new build thread, once I get some time.

The one nagging question I have is, what do people recommend for insulating walls -- that face a poured concrete wall? The house has a poured foundation, and the exterior has the Tuff n' Dry system - which I think leaves the walls "drier", but no concrete wall is ever totally dry.

My plan was to glue 3/4" XPS foam to the outside walls, then leave a 1" air gap or so, then 2x4 walls with R13 pink fiberglass.

I know that some people just do an air gap between the foundation and then do a 2x4 wall with R13 (no foam). That might be an option, but I somehow just can't wrap my head around having no protection between the concrete and the fiberglass.

I realize that there are a lot of options. What have others done that they've been happy with?

I added a poll too. I figured why not?

Thanks in advance!
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post #2 of 46 Old 07-16-2013, 07:40 AM
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3/4" XPS will give you a vapor barrier (make sure to tape the seams, calk bottom etc..)
I went with 2" xps in my last house, for more of a thermal barrier also.
I highly recommend using spray foam at your rim joists, its an area highly prone to moisture/cold infiltration/mold etc..

Good luck with the new house..

Brad
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post #3 of 46 Old 07-16-2013, 08:04 AM - Thread Starter
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Quote:
Originally Posted by KNKKNK View Post

3/4" XPS will give you a vapor barrier (make sure to tape the seams, calk bottom etc..)
I went with 2" xps in my last house, for more of a thermal barrier also.
I highly recommend using spray foam at your rim joists, its an area highly prone to moisture/cold infiltration/mold etc..

Good luck with the new house..

Brad

I'll have to look at the rim joists. I believe that they're pretty well sealed (sill-sealer, foam gap sealant, and then fluffy fiberglass with an aluminum layer). Thanks for mentioning that though, because I know that rim joists can be a big issue. The house as-is is already so tightly sealed that there is a bathroom fan (a nice quiet Panasonic one) that runs at low RPMs all the time just to get some air flow in the house.

The outside foam board is supposed to be R-2 or something (ie, not much), I figured with the XPS and the R-13 that would be enough insulation. My reluctance with going more than 3/4" or 1" is giving up more space and the increased cost.

Thanks for your thoughts!
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post #4 of 46 Old 07-16-2013, 11:26 AM
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Quote:
Originally Posted by homeav View Post

My plan was to glue 3/4" XPS foam to the outside walls, then leave a 1" air gap or so, then 2x4 walls with R13 pink fiberglass.

This should be fine, and I've seen an episode of HOH where they did this on a completely below grade interior concrete wall. The XPS will give you a little bit of a vapor barrier, but I believe it's less than what 6 mil poly would give you, which is what you want. Below grade, any vapor will push into your space from the outside, so the vapor permeability of the XPS will allow the wall to sufficiently 'breathe' in and thus not build up water (and then mold) in the wall. Some code out there demands poly, but that can actually trap water in the wall below grade. I've heard of people passing inspection, then cutting up the poly so the wall could breathe later to avoid water build up and mold growth. Above grade though, you would 6 mil poly vapor barrier as normal of course, as the wall will 'breathe' out to the exterior.
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post #5 of 46 Old 07-16-2013, 11:57 AM - Thread Starter
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Originally Posted by Swervepf View Post

This should be fine, and I've seen an episode of HOH where they did this on a completely below grade interior concrete wall. The XPS will give you a little bit of a vapor barrier, but I believe it's less than what 6 mil poly would give you, which is what you want. Below grade, any vapor will push into your space from the outside, so the vapor permeability of the XPS will allow the wall to sufficiently 'breathe' in and thus not build up water (and then mold) in the wall. Some code out there demands poly, but that can actually trap water in the wall below grade. I've heard of people passing inspection, then cutting up the poly so the wall could breathe later to avoid water build up and mold growth. Above grade though, you would 6 mil poly vapor barrier as normal of course, as the wall will 'breathe' out to the exterior.

I started reading up on the RCO (Residential Building code of Ohio) and I believe that it stated somewhere that a vapor barrier isn't required (for below grade). So I'm trying to walk that fine line of making sure that things are sealed up nicely, but not causing water build up. The poured walls aren't flat - they are that faux brick appearance (from the forms). That should make adhering the XPS a little more interesting.

The episodes that I've seen of Holmes on Homes, it seems like he pays careful attention to construction with regards to preventing mold and the like. I'd trust his (overkill) approach on most projects than some contractors.

I know I've read more than a couple places that have found that more recent research has shown that if there isn't SOME breath-ability, you're likely to have issues, I think thus why so many states have relaxed their requirements for vapor barriers.

Thanks for another comment reassuring me that my approach is okay!
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post #6 of 46 Old 07-16-2013, 12:16 PM
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I am in Canada so we have much colder temps to deal with. To save some money I used plastic for an air barrier, then the pink stuff (layered horizontally), then a framed wall with pink between the studs. Having the rigid foam boards was acceptable too though according to our local codes etc., but they are quite a bit more expensive here and I didn't think the costs was worth the space saving. Our gas company does suggest that we don't cover up all of the concrete though and we only go 4" above ground level. Then it lets the concrete breath a little.
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post #7 of 46 Old 07-16-2013, 12:30 PM - Thread Starter
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Quote:
Originally Posted by mleclair View Post

I am in Canada so we have much colder temps to deal with. To save some money I used plastic for an air barrier, then the pink stuff (layered horizontally), then a framed wall with pink between the studs. Having the rigid foam boards was acceptable too though according to our local codes etc., but they are quite a bit more expensive here and I didn't think the costs was worth the space saving. Our gas company does suggest that we don't cover up all of the concrete though and we only go 4" above ground level. Then it lets the concrete breath a little.

Interesting, OK.

I know that Canada in general can get colder than lots of the US, out of curiosity - how cold do you get in winter?

I'm in Ohio, and even in deep winter, the walls get cooler, but never enough that I've been too worried about the R-value of the insulation.

I should get an IR-thermometer and check.
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post #8 of 46 Old 07-17-2013, 10:02 AM
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post #9 of 46 Old 07-17-2013, 10:20 AM - Thread Starter
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Thank you! Some kind of best practices document was exactly what I was hoping to find.

That's a good read.

I should probably price out spray foam, but I suspect that I'll get sticker shock when I do.

This image makes me think twice about the current rim joists... Should probably add some XPS there too.

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post #10 of 46 Old 07-17-2013, 10:31 AM - Thread Starter
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This pretty well covers what I think my objective is. Except with an air gap, just so the wall framing doesn't touch the rigid insulation.

Our house doesn't have XPS on the outside either, it's just framing w/3.5-5.5" of NuWool insulation, OSB sheathing, housewrap and siding.

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post #11 of 46 Old 07-17-2013, 10:45 AM
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Spray foam is the only method I would use or endorse. Every other method has problems with moisture and/or air movement.

2" foam, R13 batts, and you're good to go.
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post #12 of 46 Old 07-17-2013, 11:22 AM
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Quote:
Originally Posted by kromkamp View Post

Spray foam is the only method I would use or endorse. Every other method has problems with moisture and/or air movement.

2" foam, R13 batts, and you're good to go.

Spray is better than pink stuff ?

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post #13 of 46 Old 07-17-2013, 11:30 AM
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Whats pink stuff - fiberglass? If so, then yes. Monumentally better. Not for acoustical reasons - for the integrity of your home.
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post #14 of 46 Old 07-17-2013, 11:36 AM - Thread Starter
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Quote:
Originally Posted by kromkamp View Post

Spray foam is the only method I would use or endorse. Every other method has problems with moisture and/or air movement.

2" foam, R13 batts, and you're good to go.

Anybody have any ballpark #s for what they paid PSF for spray foam?
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post #15 of 46 Old 07-17-2013, 11:40 AM
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In Toronto its something like $1/sq ft per inch thickness.
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post #16 of 46 Old 07-17-2013, 02:24 PM
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Another option for your rim joist might be one of the DIY spray foam kits.

There are several, heres one example..

http://www.tigerfoam.com/index.php?gclid=CIzQu9C6t7gCFS9eQgod3loAHA

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post #17 of 46 Old 07-17-2013, 05:30 PM
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post #18 of 46 Old 07-17-2013, 06:36 PM
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I bought a DIY spray kit for my rim joists that was about $350 IIRC. When I get home I'll look up the vendor for you. It was pretty easy to do.

Okay, found the email invoice. It was www.sprayfoamdirect.com
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post #19 of 46 Old 07-18-2013, 05:57 AM
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Quote:
Originally Posted by homeav View Post

Interesting, OK.

I know that Canada in general can get colder than lots of the US, out of curiosity - how cold do you get in winter?

I'm in Ohio, and even in deep winter, the walls get cooler, but never enough that I've been too worried about the R-value of the insulation.

I should get an IR-thermometer and check.

The coldest days here would get to about -40 Fahrenheit or so especially when you add in the wind factor. I am only about an hour north of the border so we are not as bad as the farther north places get. But the more insulation we can get in the better.
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post #20 of 46 Old 07-18-2013, 06:02 AM - Thread Starter
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Quote:
Originally Posted by mleclair View Post

The coldest days here would get to about -40 Fahrenheit or so especially when you add in the wind factor. I am only about an hour north of the border so we are not as bad as the farther north places get. But the more insulation we can get in the better.

Wow, that IS cold. Gives me some insight into why the big deal for Canadians and insulation.

In Ohio, it's rare that we see anything below 0f in a winter.
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post #21 of 46 Old 07-18-2013, 06:04 AM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post

good article on the flash and batt approach for insulating.

http://www.specialty-products.com/pdf/articles/FineHomebuilding0311.pdf

Thanks Big. That is a great article.

I've actually contacted a couple local insulation companies to see if I can get some quotes. I'm inclined to go for spray foam if the price isn't crazy and I can get the wife on board -- so I can do the flash and batt approach.

I got one ball-park quote of $500 for 40 feet of 9' wall. I'm guessing it's $1 something a square foot.

I'm thinking of maybe just having the ENTIRE basement covered with 1". Previously I was really only concerned with insulating around the finished space (insulation and then pink fluffy)

Anybody else just insulate the entire basement? I'm sure there would be some marginal efficiency improvement.
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post #22 of 46 Old 07-18-2013, 06:44 AM
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I researched this quite a bit before I made a decision on how to deal with my (basement) theater. In short, you need to call your local building inspector. The requirements for a vapor barrier will differ depending on your location, and it sounds like you know enough to have a good conversation with them about the options you are considering.

With regard to flash and batt, I didn't read the linked article, but that is a method of achieving better insulating performance in your above grade walls. Definitely worth considering there as it is more cost effective than just spray foam and is advertised to achieve better R values than either spray foam OR conventional batts alone. Below grade, I don't think that method provides a thick enough layer of foam to provide a vapor barrier. IIRC, you need about 2" of closed cell foam to act as a vapor barrier, but you need to double check that to make sure. Open cell foam is not a vapor barrier, so that's a non-starter for the basement walls.

You mentioned your exterior water proofing, is it a sprayed on membrane system? Are there multiple layers? One question I could never get a definitive answer to was whether that changes your vapor barrier requirements. Our house has a sprayed on membrane plus a dimpled membrane plus a drainage mat (all on the exterior), so the question was does that provide a vapor barrier on the outside of the house? Our concrete walls are dry! There's much more moisture in the basement air than coming through those walls.

At any rate, if I had it to do over, I would have had 2" of closed cell foam sprayed on our walls, and had them trim it. Even with a vapor barrier on the exterior, and the sprayed foam vapor barrier on the interior, there is no organic material to develop mold. So trapping moisture between is not a problem. Then I would have framed my wall with about 1" air gap between the foam and the 2x's for decoupling. Then used regular fiberglass batts in the wall cavities for sound absorption.

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post #23 of 46 Old 07-18-2013, 07:17 AM - Thread Starter
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Quote:
Originally Posted by J_P_A View Post

I researched this quite a bit before I made a decision on how to deal with my (basement) theater. In short, you need to call your local building inspector. The requirements for a vapor barrier will differ depending on your location, and it sounds like you know enough to have a good conversation with them about the options you are considering.

With regard to flash and batt, I didn't read the linked article, but that is a method of achieving better insulating performance in your above grade walls. Definitely worth considering there as it is more cost effective than just spray foam and is advertised to achieve better R values than either spray foam OR conventional batts alone. Below grade, I don't think that method provides a thick enough layer of foam to provide a vapor barrier. IIRC, you need about 2" of closed cell foam to act as a vapor barrier, but you need to double check that to make sure. Open cell foam is not a vapor barrier, so that's a non-starter for the basement walls.

You mentioned your exterior water proofing, is it a sprayed on membrane system? Are there multiple layers? One question I could never get a definitive answer to was whether that changes your vapor barrier requirements. Our house has a sprayed on membrane plus a dimpled membrane plus a drainage mat (all on the exterior), so the question was does that provide a vapor barrier on the outside of the house? Our concrete walls are dry! There's much more moisture in the basement air than coming through those walls.

At any rate, if I had it to do over, I would have had 2" of closed cell foam sprayed on our walls, and had them trim it. Even with a vapor barrier on the exterior, and the sprayed foam vapor barrier on the interior, there is no organic material to develop mold. So trapping moisture between is not a problem. Then I would have framed my wall with about 1" air gap between the foam and the 2x's for decoupling. Then used regular fiberglass batts in the wall cavities for sound absorption.

From what I understand about the exterior system, it's 60mil of a rubber/asphalt type covering, and then a 1" (?) layer of a fibrous board that has some insulation, but also allows for drainage. It reminds me of rigid acoustic fiberglass. It's funny you mention your walls being dry. I bet the walls on my new house are quite dry too. Any moisture seems to be from the floor (and that's in part because the builder doesn't seem to understand that cheapo sump pumps don't run when you jam the float against the sump wall.......... 3 times now)

Some info here:
https://www.tremcobarriersolutions.com/products/default.asp?id=1

Around 1:30 here is an actual installation example:

Based on this, I'd have to say that it is a vapor barrier, right??
http://www.tremcobarriersolutions.com/fileshare/specs/TBS-0037TNDSpecSheet.pdf

"Water Vapor Permeance test results were <1 perm for a 40-mil dry coating" (I believe that thickness is if they apply it correctly)
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post #24 of 46 Old 07-18-2013, 07:28 AM
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Somewhere between a class II and class III. I believe closed cell spray foam is a class II vapor retarder, and open cell is a class III.
Quote:
  • Class I: Less than or equal to 0.1 perm [e.g., polyethylene];
  • Class II: Greater than 0.1 perm but less than or equal to 1.0 perm [e.g., kraft facing];
  • Class III: Greater than 1.0 perm but less than or equal to 10 perm [e.g., latex paint].

Still, you're basement should be very dry if installed correctly. I would still recommend calling your local inspector to find out what is appropriate in your area. If you decide to go with one, I would still recommend the closed cell spray foam at 2" (again, IIRC) because it will not support mold growth.

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post #25 of 46 Old 07-18-2013, 08:26 AM - Thread Starter
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Thanks JPA.

I'll see if I can talk to someone in the county inspection department to see what they recommend.

The city building office is nearly useless (Sure, there is code, but they don't care about enforcement, only revenue). The county office is supposed to be quite good (per the home inspector /structural engineer I hired a ways back).
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post #26 of 46 Old 07-18-2013, 10:55 AM
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Quote:
Originally Posted by J_P_A View Post

At any rate, if I had it to do over, I would have had 2" of closed cell foam sprayed on our walls, and had them trim it. Even with a vapor barrier on the exterior, and the sprayed foam vapor barrier on the interior, there is no organic material to develop mold. So trapping moisture between is not a problem. Then I would have framed my wall with about 1" air gap between the foam and the 2x's for decoupling. Then used regular fiberglass batts in the wall cavities for sound absorption.

Agreed 100%
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post #27 of 46 Old 07-18-2013, 11:20 AM - Thread Starter
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Well, after trying to seek some recommendations on closed cell thickness vs XPS from an inspector -- this threw me for a loop:
"You don't want to have insulation behind your framed wall because you are making two vapor barriers that could trap moisture between them."

I could see that, if you weren't trying to build an acoustically isolated wall. Thoughts? In my mind, it all depends on what you consider "a vapor barrier".

His additional comment was that if you're going to insulate the exterior wall, and then insulate the framed wall........... You want them touching, rather than leaving a gap (that could trap moisture).

Is this just a case of "Very rarely seen (wall, insulation, gap, insulated/frame wall) , so it sounds wrong?" He said that he rarely sees the exterior wall insulated in addition to the framed wall (I'm sure because of cost, but still)
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post #28 of 46 Old 07-18-2013, 11:53 AM
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Your batt insulation should not have a kraft paper facing, so it will not have a vapor barrier. I'm not sure I understand why you would want them touching in any case, though? I'm also not sure I follow how the gap would catch moisture.

However, as long as the foam is sufficient thickness, it should not hurt to have the batt insulation touching the foam. You won't have any moisture there anyway. You DO NOT want your framing touching the foam. This will couple the wall to the foam/foundation and reduce your acoustic isolation. This may be part of the issue your inspector didn't follow. The batt insulation has nothing to do with thermal insulation in this application. You are only adding the batt insulation to absorb sound that escapes your room and to prevent any sort of resonant cavity.

I think my return call to the inspector would be along the lines of what do I need to do to my exterior walls to ensure I'm met the vapor barrier requirements in my area. I probably wouldn't mention the room I'm building just inside of those walls because it doesn't matter. If you've provided a true vapor barrier, you shouldn't have a moisture problem. The foam should provide enough R value to prevent any moist air from condensing on the walls as well (maybe that's what the inspector is getting at).

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post #29 of 46 Old 07-18-2013, 12:05 PM - Thread Starter
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Quote:
Originally Posted by J_P_A View Post

Your batt insulation should not have a kraft paper facing, so it will not have a vapor barrier. I'm not sure I understand why you would want them touching in any case, though? I'm also not sure I follow how the gap would catch moisture.

However, as long as the foam is sufficient thickness, it should not hurt to have the batt insulation touching the foam. You won't have any moisture there anyway. You DO NOT want your framing touching the foam. This will couple the wall to the foam/foundation and reduce your acoustic isolation. This may be part of the issue your inspector didn't follow. The batt insulation has nothing to do with thermal insulation in this application. You are only adding the batt insulation to absorb sound that escapes your room and to prevent any sort of resonant cavity.

I think my return call to the inspector would be along the lines of what do I need to do to my exterior walls to ensure I'm met the vapor barrier requirements in my area. I probably wouldn't mention the room I'm building just inside of those walls because it doesn't matter. If you've provided a true vapor barrier, you shouldn't have a moisture problem. The foam should provide enough R value to prevent any moist air from condensing on the walls as well (maybe that's what the inspector is getting at).

It's probably about time that I dig up the actual code requirement. It's a statewide building code that the counties/cities follow, so nothing unusual in the local codes that I'm aware of.

Ohio takes the International Building Code and they "Ohio-ize" it, basically paraphrase it and delete certain components, but follow almost all of it. The stuff they delete is stuff that I like and home builders say "that stuff costs too much money..."
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post #30 of 46 Old 07-19-2013, 09:19 AM
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Originally Posted by J_P_A View Post

Your batt insulation should not have a kraft paper facing, so it will not have a vapor barrier. I'm not sure I understand why you would want them touching in any case, though? I'm also not sure I follow how the gap would catch moisture.

However, as long as the foam is sufficient thickness, it should not hurt to have the batt insulation touching the foam. You won't have any moisture there anyway. You DO NOT want your framing touching the foam. This will couple the wall to the foam/foundation and reduce your acoustic isolation. This may be part of the issue your inspector didn't follow. The batt insulation has nothing to do with thermal insulation in this application. You are only adding the batt insulation to absorb sound that escapes your room and to prevent any sort of resonant cavity.

Once again I 100% agree. With this insulation methodology you do not have a vapor barrier to the inside of the wall - the foam is your vapor barrier. If you had enough batt insulation in place (like 12" or something extreme) this could be problematic, but with standard 2x4 batts you are fine. BSC has done very robust simulations for this methodology to show the average moisture movement and dew point inside the wall over a typical 12 month cycle.

The stud wall must not touch the spray foam, but the batts can be pushed right up against the spray foam. This is desirable to minimize air movement behind the stud walls.
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