Wall Insulation - Looking for Opinions

[Nelson]

Hi All-

We are in the middle of renovating two bathrooms in our house, one of which is in our walk-out basement. My question revolves around the basement. The bathroom in the basement sits between two bedrooms. We ended up building some new walls in this bathroom which resulted in ripping out 1/4 of the drywall in one of the bedrooms. The exterior wall for this bedroom is all above grade. Since I already have some drywall ripped out in that room, I am considering ripping out the drywall on the exterior wall and fixing the insulation behind it. Since this house was built in the 1970s, this wall has paper-face FG insulation with a vapor barrier (plastic) over top. We know now that this is bad. I haven't seen any evidence of bad mold but I still want to fix it.

Sooo, on to my question. I'm looking for opinions on the best way to insulate this wall. It's a standard 2x4 with aluminum siding on the exterior (not sure what the sheathing is). My inital instinct was to go the spray foam (closed cell) route at about 2 inches to get me to R10 or R11, which I think is about as good as I'm going to do with a 2x4 wall without doing foam board on the outside and, thus, having to redo siding - not something that's in the cards at the moment. I also considered foam board, using spray foam to seal around the board and the wood framing, though I don't know if I can get as good a R-level with a 2x4 wall - this would also be more work than spray foam.

At any rate, would love to hear some opinions...

Thanks!

 

[semipro]

One option is to spray open cell foam in the stud bays and then install mold resistant drywall with a water permeable covering such as latex paint (not oil based paint or vinyl wallpaper). There's no reason you can't fill the whole 3.5" depth to get an R value of about 12.

I suggest open cell foam rather than closed cell since you don't know what's under the aluminum siding. The open cell foam will more readily allow any moisture trapped between the sheathing and insulation to dry inward.

Depending on how much needs to be done you'll probably find its cheaper to contract a foam sprayer rather than DIY. The DIY foam kits are very expensive per volume and R-value. Edit: by material volume DIY spray foam is 2-3 times the cost of foam panel. I recommend a hybrid application where panels are used to fill wide open spaces and spray foam is used in the more complex areas, usually side by side in the same wall assembly.

Two other options: fill the stud bays with a foam board and seal with canned spray foam as you mentioned. Roxul, mineral wool is also a good option but won't provide as much air sealing. It is easy to work with though and will yield R14 in a 2x4 wall. The latest issue of Fine Home Building has a great article on mineral-wool insulation and I, personally, love working with the stuff.

BTW, interior poly vapor retarders are still recommended in very cold regions.

 

[Nelson]

Thanks much SemiPro. I've been looking at the DIY kits, mostly because I'm working with a tight schedule and I don't know if I can get someone out here before the drywall goes up. The tricky part is that I'm trying to manage this work into the two bathroom remodel, which is a pain all on it's own! As far as Open or Closed - what kind of shealting/underlayment would make you choose one over the other? Does it have to do with the vapor permability of said sheathing/underlayment?

I've thought about using foam to air seal the stud bays and then doing FG or Roxul - preferably roxul/mineral wool if I can find it. Anyone here gone this route?

 

[semipro]

As far as Open or Closed - what kind of shealting/underlayment would make you choose one over the other? Does it have to do with the vapor permability of said sheathing/underlayment?

If the sheathing was relatively vapor tight (e.g. aluminum foil coated something) I'd be wary of using closed cell foam since it has a much lower permeability. If tar paper or housewrap like Tyvek, which is vapor permeable, I would not be as concerned about trapping moisture. Open cell foam tends to be more elastic and may adhere to sheathing/studs better for better air sealing. One of the criticisms of sprayed foam is that it pulls away from what it's sprayed on and air sealing is lost.
Good reference here: http://www.greenbuildingadvisor.com/green-basics/spray-foam-insulation-open-and-closed-cell

Edit: BTW, when I compared the price of board foam vs. contractor applied spray vs. DIY spray, the DIY was much more expensive. Look at the board-feet you get and the resultant R-value.

 

[semipro]

I've thought about using foam to air seal the stud bays and then doing FG or Roxul - preferably roxul/mineral wool if I can find it. Anyone here gone this route?

I've done this with a pro foam applicator gun for just the seams, then installed Roxul. It seemed to work well but its challenging to seal at all seams, including those between framing elements, I generally do those with caulk rather than foam. (e.g., the gap between stud and sill plate or top plate, that faces the room interior).

 

[Nelson]

Cool - unfortnately, looks like that link is for Prime members only.

I've done a fair amount of air sealing so I'm not afraid of taking that challange on. I've only used the Great Stuff in the cans with the plastic applicator - may have to invest in the pro gun if I go the seal and batt route. The challange I'm seeing with Roxul is that I can't find it around here expect for a pallet of 12 bags, which is more than I need at the moment. I see that Owens has their version called ThermaFiber which it looks like I might be able to get by the bag. My assumption is that the differences between Roxul and ThermaFiber would be minimal, if any but haven't used either product.

 

[semipro]

Cool - unfortnately, looks like that link is for Prime members only.

Sorry about that. It was working for me now I'm being told I can't view it either.

 

[Nelson]

So, another question. If I go the seal/batt route, what have others done for the seal portion? I was thinking spary can foam, but I'm wondering if it might be easier/more economical to caulk. If caulk, what type of caulk?

 

[Wisneaky]

Since you live in Wisconsin I'd recommend going to your closest Menards store and buying a big froth pak. Spray foam the cavities an inch or two thick and any outside walls put up a poly vapor barrier before installing the drywall. I used this is my crawl space and it's amazing. If I could do it all over again I would have done all my walls with it.

 

[Wildo]

If you're looking to do the bays as well a contractor is the way to go. Your state may offer a rebate as well. Closed cell will get you over R-20 if you fill the 2x4. You can find out what kind of sheathing in under 10 minutes total by unhooking the bottom row of siding to take a peek. I love my sprayfoam.

 

[semipro]

So, another question. If I go the seal/batt route, what have others done for the seal portion? I was thinking spary can foam, but I'm wondering if it might be easier/more economical to caulk. If caulk, what type of caulk?

There was an interesting evaluation done by the Journal of LIght Construction on air sealing materials including caulks, tapes, etc. One finding that surprised me was that Liquid Nails did a really good job of sealing between different boards and a wiring penetrations. I can attest to how well liquid nails works after tearing out our basement walls for remodeling. The stuff is tough!
That said, there are many good caulks for air sealing out there. I think that main thing to keep in mind is that they do not work well in larger gaps unless you use foam backer.
The JLC article is here (I hope): http://tinyurl.com/ova3mwf

 

[johneh]

I'm a fan of closed cell spray foam
not only can you get great R value
but closed cell gives you a thermal break
is water proof and no air infiltration .
It keeps you nice and warm and draft free
in one application

 

[semipro]

I've only used the Great Stuff in the cans with the plastic applicator - may have to invest in the pro gun if I go the seal and batt route.

This may interest you: https://www.hearth.com/talk/threads/multi-use-foam-applicator-gun-follow-up.107613/

 

[velvetfoot]

I have something similar. It's a lot less messy than the cans. You can use it a little, put it down, and use it again months later.
I wonder if you can buy 3.5" thick foam boards? I know there are 2" boards and I think 1.5".

 

[Wisneaky]

I have something similar. It's a lot less messy than the cans. You can use it a little, put it down, and use it again months later.
I wonder if you can buy 3.5" thick foam boards? I know there are 2" boards and I think 1.5".

Rigid foam is expensive and you still need to seal around the edges.

 

[velvetfoot]

Rigid foam is expensive and you still need to seal around the edges.

True. But sealing won't be as bad with the gun. And you can do it all yourself without relying on someone else. It'd be good to get estimates.

 

[Wisneaky]

I wouldn't use cans of foam at all. That stuff is messy and real crap to work with. Better off going spray foam.

 

[semipro]

Rigid foam is expensive and you still need to seal around the edges

Rigid panel foam is 1/3 to 1/2 the price of DIY spray foam like Dow Froth-Pak by end-product volume.
The advertised R-value of the Froth-Pak is 6.1 (per inch thickness) as compared to 5 for XPS foam board though.

As I noted above:

Edit: by material volume DIY spray foam is 2-3 times the cost of foam panel. I recommend a hybrid application where panels are used to fill wide open spaces and spray foam is used in the more complex areas, usually side by side in the same wall assembly.

 

[velvetfoot]

Perhaps a first time user might not do as well as advertised, lol.

 

[Wisneaky]

Rigid panel foam is 1/3 to 1/2 the price of DIY spray foam like Dow Froth-Pak by end-product volume.
The advertised R-value of the Froth-Pak is 6.1 (per inch thickness) as compared to 5 for XPS foam board though.

View attachment 162409

As I noted above:

Your rights. Wasn't thinking correctly when I posted that comment. You still need to seal around the edges with rigid foam or you'll have air intrusion.

 

[semipro]

My go-to method for insulating exterior stud bays lately for remodeling has been:

1. Using a commercial canned spray foam applicator or caulk to seal the seams/cracks
2. Installing a 1" layer of XPS board installed against the sheathing
3. Use canned foam to seal in the foam panel
   
4. Installing rock wool batt insulation (e.g. Roxul) against the foam board.

I may use thicker foam if the studs are larger than 3.5" deep.

That said, if I was doing new construction and everything was opened up I'd just have a contractor spray it all.

 

[Nelson]

My go-to method for insulating exterior stud bays lately for remodeling has been:

1. Using a commercial canned spray foam applicator or caulk to seal the seams/cracks
2. Installing a 1" layer of XPS board installed against the sheathing
3. Use canned foam to seal in the foam panel
   
4. Installing rock wool batt insulation (e.g. Roxul) against the foam board.

I may use thicker foam if the studs are larger than 3.5" deep.

That said, if I was doing new construction and everything was opened up I'd just have a contractor spray it all.

I believe the Roxul I'm looking at is 3.5" thick - does it compress easily enough to fit a 1" XPS board behind it? Also, what is the thought process behind the 1" XPS board? Extra R-value, vapor issues?

Thanks for all the replies so far!

 

[johneh]

If you compress bat insulation you are defeating its purpose
you loss insulating value if it is compressed

 

[semipro]

The Roxul I've purchased at Lowes was 3" thick so not an issue for me.
The foam was added to help with air sealing while adding some thermal insulation.
Most of our exterior walls are built with 2x6s and I've only round Roxul in 3 and 3.5 in. thickness so I tend to add the foam board to fill the space.
Fiberglass is relatively easy to compress and resulting R values are affected as johneh mentions: http://www2.owenscorning.com/literature/pdfs/10017857 Building Insul Compressed R-Value Chart Tech Bulletin.pdf
I would not try to compress Roxul much. It is much more "solid" than fiberglass. This makes it great to work with though. It fills cavities more tightly and is great to cut. I compare it to cutting bread. In fact, a serrated bread knife works on it very well.

 

[Nelson]

Ah, ok. I think the stuff I'm looking at around here is 3.5" so I I would have to skip the XPS, though I believe the XPS would act as thermal retarder which may be good or bad.