Advice on Wall Assembly
Hi just joined I kept reading articles that I couldn’t finish lol. So I had to learn more. I just bought what for me is a dream property in my small town right across from one of my favorite fishing holes. I am in zone 6 and having lots of trouble planning my envelope.
Now the struggle has begun. I’m lost on a wall system that won’t cause moisture and can still give me a high r value. So many people in our area I’m in Wisconsin all do the bare minimum. I have watched so many videos and seen so many different forms of high efficient wall systems but I’m not sure what style will work for me in my area. I could only find one consultant amd she worked for a builder and said she did t have time to assist me.
I see this build guy on you tube he uses zip and makes everything in the envelope super tight with many layers of insulation inside and out but in my mind is this causing moisture issues or because it’s so tight is it ok.
We aren’t rich and my house isn’t huge but I still want to do everything I can to insulate as well as possible and make it as air tight as possible but very cost effective. I’m really looking for some options on wall systems in may area that will do well and not have moisture issues. I’d rather ask now learn spend the money up front then have problems later. I already have a line on some quality windows and now good wi Dow taping techniques etc some of these things I know well and practice but I fell like my knowledge on the building envelope is alluding me and I want to do better not only for myself but for my clients moving forward.
I appreciate any thoughts things to read and any real world wall systems that could work for me. Also glad to be part of the community.
also apologize if not in the right question area
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Welcome to GBA! Now that you are a member, you have access to this article, which might help inform how to approach your wall assembly: Walls that Work. It details five assemblies, noting the climate zones where they will perform well.
Tightness (usually this means AIR tightness) isn't what causes moisture issues. Mositure issues come from interior leaks (indoor air leaking into the wall), and insulation materials not being quite right for the application. The old "houses need to breathe" argument was really a band aid for poor construction practices. Air leaks are energy loss.
For someone using Zip, and note that there are two kinds of "Zip", one is Zip-R that includes rigid foam insulation, the other is "regular" Zip which is just OSB with the green coating on the exterior side that acts as a WRB similar to housewrap. You'll find articles on GBA about "exterior rigid foam", and those articles will give you minimum amounts of rigid foam needed in your climate zone to avoid mositure issues in your walls. You could use Zip-R to do this, or you could use regular sheathing (or even regular Zip sheathing), with rigid foam installed over that.
A typical build that is simple and safe would be a typical wall with batts, then exterior rigid foam over the exterior sheathing. You could, for example, build a 2x4 wall with R15 batts and another R13 worth of polyiso (2" thick) on the exterior. This would give you an R28 wall, but would perform better than R28 batts would (that's not really a common size, but this is just a simple example), since the exterior rigid foam helps a lot with thermal bridging of the studs. You'd then want to install your drywal using the airtight method on the interior to help to keep any interior air from leaking into the wall.
Most of the time moisture problems are due to warm, moist air leaking from inside the home into wall that isn't well sealed. That's where the bulk of the moisture comes from. The insulation, if you're using rigid foam, keeps the structure of the wall warm enough that anything that does make it into the wall won't condense out into liquid water and cause problems.
There are other ways to build a wall, but the type in my example is probably the simplest and most easily understood.
You can save money using reclaimed or B stock rigid foam. You'll still want to seal up the exterior to keep out the weather.
Bill
I’m not familiar with the air tight method but I would be using a 2x6 exterior walls and then hopefully batts and exterior foam.
The part that loses me is the drying to the inside and the different vapor barriers. For instance in my area they require 6 mil plastic over the I write of insulation because of the building code it based on my knowledge this would cause moisture in a heavily insulated wall.
Thanks for the comment I’m committed to building a greener house and will do whatever research is necessary.
"6 mil plastic" probably means polyethylene sheet, which is a true vapor BARRIER. It's better to use a smart vapor RETARDER instead, if your local building people are OK with that. Typical products like that are Membrain and Intello, although there have been some recent reports of Membrain being difficult to get at the moment, and my quick check of that a day or two ago confirmed that. I don't know what the issue is there.
If you have to use poly on the inside, it would be good to allow some drying to the outside, but that can be difficult to do if you want to use exterior rigid foam. EPS is the most vapor open of the common rigid foam types, but you'll need more of it in terms of thickness to reach the required R value for your climate zone. Polyiso gives you the best R per inch, but the more common versions have a foil facing which is a vapor barrier. You could use fiberglass or kraft faced polyiso instead, which is more vapor open, but it's not as readily available unless you order through a commerical insulation supply house.
What you want to try to avoid is a vapor BARRIER on BOTH sides of the wall. That can trap moisture.
BTW, the "air tight drywall method" is explained in some GBA articles. It's simple, really, mostly you just put a bead of sealant around the perimeter of the wall before you put the drywall up so that the edges are all sealed to the framing. You have to air seal any penetrations in the wall (wires, pipes, etc.), and you have to seal any electrical boxes. The goal is to have the drywall acting as an air barrier, so you don't want any air leaks anywhere.
Bill
Thanks for the comments. I have also been thinking about a smart vapor barrier. I’m guessing that controlling the humidity level and keeping it around 30% year round would be ideal as well. Like an whole home dehumidifier.
I wonder if using tyvek and then multiple layers of comfort board or rockwool panels with a rain screen would work because then it is vapor open I think. I will keep researching the main point being make sure the wall can breather each way. This may be a dumb question but if the drywall is really sealed up wouldn’t that than cause a moisture problem?
Thanks again for the comments
If the drywall is sealed up airtight, then air will not leak through the drywall layer (and then through your wall layers toward the cold exterior). If air does get through a wall during winter, as the air cools off moving toward the exterior, it will condense moisture somewhere (during your cold winters). Likely that would be your sheathing, which can rot over time. So the airtight drywall method is a good practice.
Note that drywall will allow some moisture to migrate through the drywall itself, even if no air leaks. You can reduce this movement during winter months (when interior humidity is much higher than exterior humidity) by using a smart vapor retarder as Bill suggested. That would block vapor getting into the wall in winter, yet allow drying to the interior during the summer (to dry out the wall). That's why its referred to as "smart." Or a vapor retarding latex paint would help minimize water vapor flow into the wall during winter.
Comfortboard instead of polyiso or foam outboard of the sheathing would be good too, as its vapor open as you noted. However its not cheap, and a bit difficult to install. It can compress and if you are not careful, your exterior wall plane could end up a little wavy rather than a nice flat plane for your rainscreen and siding.