Wall Layers
Hi there, I am converting a barn into a guest house and wanted to get some input on whether or not my proposed wall layers will work (I.e., will I be creating a moisture issue, etc.). Layers:
1. Shingles
2. House Wrap
3. Plywood Sheathing
^(note I will be replacing the existing wrap and sheathing eventually with zip system – but not for at least a year or two)
4. 2×6 Mineral Wool Batts
^(note, 2×4 Wall furred out with 1” rigid foam and 1” wood strips)
5. Drywall & latex paint
Key questions I have:
-Do I need a vapor barrier between 4 & 5? If so what kind and thickness? I’m in Maine if climate matters.
-Will the eventual zip system install (replacing 2 &3) create any issues?
On a side note I also have a lot of 2” thick rigid foam insulation that I got for free – could that be useful here? It was cut to fit stud bays by person I got it from, but I’m unsure how to use it effectively now that it’s cut to bays…
thanks!
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Replies
Climate zone definitely matters when it comes to vapor control. If you are in the colder side of Maine, you would want a warm side vapor retarder. Usually the best is a smart vapor retarders (or craft faced batts) but interior poly also works.
This assumes a house that will be occupied full time, with a guest house there isn't a lot of continuous moisture source in the winter time, vapor control matters less, you can also skip it. I like to include it, since with a bit of care, it can be detailed as your secondary air barrier and backup for the eventual cracks in your drywall.
With enough exterior rigid insulation, you can skip this completely but you need between R12 to R15 depending on which climate zone you are in. This extra insulation is probably not worth it if you have a free source of 2" EPS.
Exterior rigid does make a big difference for energy use, but I don't know if it is worth it unless you are heating the place year round. You can definitely use the narrow strips you have by installing them horizontally. Increasing your wall to 2x6 with foam strips is probably your biggest energy savings.
There is no problems with interior poly and exterior rigid (standard install around me).
Thanks! For a smart membrane would I be alright with Membrain from Certainteed?
On the rigid use I had a question- Do you have a picture of what you’re suggesting? I had been planning to use some 1” rigid and 1” wood strips to furr out the 2x4 walls by 2”. Do you think it would be better to use 2” rigid strips? I guess I would need to put drywall furring strips over that with extra long screws? Just wondering how I’d affix drywall, electrical boxes etc.
Thanks again!
Membrain is one of the products, more available than some of the other ones.
I assumed your doing something like this for your wall on the interior:
https://www.finehomebuilding.com/2014/11/26/breaking-the-thermal-bridge
The foam strips I was talking about are the 14.5" wide 2" pieces you have for the exterior.
P.S. 1.25" of foam plus 3/4" plywood strips are better as they are less likely to split.
Yes that’s what I was thinking! Thanks!
I'm doing a Bonfig wall right now and this is what I've learned...
1. The 1x wood splits, bends, and is a pain to work with. Maybe you're getting better 1x than I am, but go with 3/4 plywood and rip it into strips.
2. Get a denser foam. Anything less than 25psf will compress and make your walls wavy.
3. Make sure you use long ring shank nails or long screws to put these on.
4. Even with a denser foam and plywood you should be prepared for some shimming before drywall.
Hi Akos - quick question on the plywood. I have a bunch of old growth fence boards (with very tight rings) that I’ve saved. Do you think those would be more resistant to splitting if I ripped those down (vs. plywood)? Trying to use what I have around the farm as much as possible. Thanks!
I would give it a try, would definitely be better than the box store 1x2 lumber.
I generally find that plywood is much more forgiving if you are looking to install them with a framing nailer.
"1. Shingles
2. House Wrap
3. Plywood Sheathing
^(note I will be replacing the existing wrap and sheathing eventually with zip system – but not for at least a year or two)"
Really? You want to do all this work now, and then rip off all the shingles and plywood just to put on a different sheathing and shingles? Seems like a lot of work and money unless there's something more going on.
Make sure that the wall complies with the recommendations in Table 2 A or B here.