How to afford high performance walls in zone 6 with no spray foam
We are trying to afford a 1200sf home and would like to shoot for the Pretty Good House goals for walls in zone 6 (R40), along with as low-toxicity of materials as possible.
We wanted (outside to inside): board on board siding, rain screen, 4” rockwool Comfortboard, mento, plywood, 2×6” filled with cellulose, Intello, service cavity, drywall with clay based paint.
Our builder says this will double an already high number for the cost of the house.
I don’t want to use spray foam, and would prefer no foam at all, but it seems like ZipR (instead of plywood/rockwool/mento) would be much easier to install and therefore get us pretty close to Pretty Good in terms of insulation (I think the highest ZipR panels are R13 or so), although I am not happy with OSB and additionally wonder if it’s okay to have it hanging out on the exterior like that, even with a rain screen.
I would appreciate any suggestions or words of wisdom!
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My Pretty Good House co-author and frequent collaborator Dan Kolbert wrote a very good article about double stud walls: https://www.finehomebuilding.com/project-guides/insulation/a-case-for-double-stud-walls. We both use them regularly.
If you have a decent cellulose installer--one familiar with the techniques required for filling deep bays, including higher-than-normal density--there is no need for other types of insulation in the assembly. Zip-R is only slightly more vapor-retarding than plain Zip, but even plain Zip is at the limit of what I consider a safe vapor retarder for sheathing a double-stud wall. Mineral wool is expensive compared to cellulose, with no added benefit except slightly higher R/in.
Builders fall into four categories:
• Ones who think double-stud walls are far easier and less expensive than using continuous exterior insulation;
• Ones who think exterior insulation is far easier and less expensive than double-stud walls:
• Ones who find them equivalent; and
• Ones who find both to be dumb and wish it were 1950 again.
If you simplify your assembly and your builder still balks, ask how they would get you to true R-40 walls.
Exterior insulation is crushingly expensive. Double stud walls are far less labor intensive and more approachable. Bonfiglioli walls are my baseline, price point standard.
There are exceptions where exterior insulation could make sense- mostly involving retrofits. If your new home is a simple box with minimal detailing, exterior insulation could be an option- but more than likely, another approach will be more cost effective.
Is your budget appropriate for the project? Your question casts a very broad net. Your builder should have systems that he's comfortable in implementing. What has he proposed? Does he have experience with these more robust systems?
ZipR is not a good product. If your building is steering you in this direction, find another builder.
Are you working with an architect or designer?
Climbing carpenter,
I agree with much of what you said. I too like double stud walls. Can you elaborate on the "ZipR is not a good product" statement?
Consider doing your 2x6 wall with 2x6 top and bottom plates (and king studs) but then 2x4 framing at 12" oc and offset, so you have a nailing surface every 24". This increases the effective R value because it reduces thermal transfer between the studs.
At the time I had mine priced, the following were the costs:
a. 2x6 walls standard construction (16" oc) with standard zip = baseline
b. 2x6 walls with offset studs at 12" oc as described above = baseline ($100 difference which is negligable) because the 2x4 vertical stud board foot price was so much less than the 2x6 board foot price
c. 2x4 walls standard construction + ZipR = about 10% more than baseline
I went with option b. With all options, insulation is damp applied cellulose (vs dense pack). However, not sure why @climbing_carpenter believes ZipR is not a good product...have not heard that before. There are pros and cons to many products...
Also recognize that part of your contractors pricing is the "don't want to mess with it" factor. If they are not familiar with something, they tend to overprice it. With the exterior insulation, the contractor has to price in how to deal with the window bucks, etc. ZipR solves this by allowing them to nail the window flanges to the ZipR.
It is worth sitting down with your contractor and reviewing which details are adding the most cost, and using that knowledge to select a system that won't scare your contractor, and will also then get you an affordable price. This is another way of saying the price you are getting may not be related to the actual cost of labor and materials, but there is not much you can do to change that other than get your contractor comfortable with the system you settle upon.
Conway NH? We're neighbors!
ZipR presents a myriad of structural complications- that conversation could be long.
From a performance perspective- the stuff fails. Each fastener is a point bridge, and because so many nails (spikes, at that- metal) are required, ZipR does not mitigate thermal bridging as marketed.
Also, it's cheap OSB which does not pass the test of time. On many occasions I have encountered OSB that has been compromised for one reason or another where plywood has been fine in similar situations. Advantech is a good product, but it is less vapor open. Zip is newer- we'll have a better understanding of its long term suitability in the coming decades.
That said, as Zip (not ZipR) has become ubiquitous, the performance standard of new houses has inadvertently improved- immensely. I'm a fan of Zip in production level building.
Climbing carpenter,
I don't want to hijack the thread, but I have been monitoring a wall with sensors on the outside, just inside the foam, and on the inside face of the wall and can see that ZipR appears to be reducing heat flow well. Although I agree plywood is preferable to osb. Happy building.
That won't do the trick- you'll need an IR camera, particularly at the panel edges. We're not talking about center cavity. The gazillion nails will light up like a xmas tree. Double stud walls and exterior insulation do a lot more to mitigate bridging.
A 2x8 wall with studs at 24"OC will outperform ZipR (of similar resilience) and meet our code requirements.
Don't forget that the emissivity of galv steel is roughly a factor of 3 lower than the emissivity of OSB (not sure the emissivity of the ZIP coating), so some of what you're likely seeing is from the emissivity mismatch and reflected IR (your IR camera is probably exaggerating). If the nails are taped over, the emissivity will be much closer between the two.
The first question is in your mind what is high performance and how do you define it?
It sounds to me like you have tasted the passive house Kool Aid but have not swallowed.
From an economic point of view R40 walls do not work they simply cost so much to build that they can never recover their costs.
I do not see the appeal of the Zip+R I think it weakens the walls by putting the squishy foam between the frame and the sheeting no matter how many more nails you install.
You may find this article interesting.
https://www.greenbuildingadvisor.com/article/how-to-design-a-wall
If you decide your idea of high performance is the home that costs the least to build and operate. Consider building a computer model of your home. Enter the costs for each option and let the numbers make the choices. The BEopt program is free to use but you will have 20-40 hours to learn it and build your model.
https://www2.nrel.gov/buildings/beopt
16 Training videos
https://www.youtube.com/playlist?list=PLHC0xDtkdjgec8QhVt7exJY3tpSLEFk-d
Walta
Thank you all for so many ideas. I’m going to re read them when the kids go to sleep, and present to my spouse. I did chat briefly with the builder we’ve been hoping to use, but he will need several more weeks to come up with estimates. I now understand that his limiting factor is that he prefers to build off-site and bring in wall and roof sections on a giant flatbed. Which excludes double stud walls and other things. And he is the only “high performance” builder I can find anywhere remotely near our rural location, and my courage flags when I try to figure out how to make other builders excited about the prospect of high performance membranes and careful air sealing etc.
Our biggest priorities (after budget) are to prevent mold and reduce toxicity/offgassing. It’s been a very long road of unstable and often unhealthy housing for our family of 8, and we are so ready to live in our 1200sf haven and regain our collective health…just as soon as we figure out how to design and build it!
"I now understand that his limiting factor is that he prefers to build off-site and bring in wall and roof sections on a giant flatbed."
This is NO WAY should exclude double stud walls- the exterior bearing walls can be panelized off site, while the interior of the assembly stick built on site- heck, with careful work, these can be built off site too, but it isn't really worth the effort. They're quick, like interior partitions (which can -and in some case are- built off site too!)
Where are you located? Use the PHIUS and PHI websites to locate certified builders- this does not commit you to a standard of construction or certification, but may lead to a builder in your region who is better informed. Further, 1200 square feet is small. You do not need a production builder. An experienced carpenter who values their craft could do just as well.
If building off-site and you want high R value, the simplest is climbing_carpenter's earlier suggestion of 2x8 studs 24OC. With high density R30 batts that gets you a pretty good wall for not much money.
If you want more R value, you can add Zip R6 to the outside or step up to 2x10s.
These are simple to build and insulate especially if you have local dense pack installers. Pretty standard construction and there is not much material cost between 2x6 16" vs 2x8 24".
Any of these walls will require a vapor retarder (faced batts or membrane) under the drywall in cold climate.
@sarabeth_Matilsky
Since you have have located a "high performance" builder, you are on the right track. You are correct that getting another builder to do this is like fitting a square peg in a round hole.
Ideally, your builder has some expertise, and has developed systems that work for that builders business.
Your best bet is to tell you builder your priorities, which sound like budget and health. Then define the budget, and health as you have defined it for us is preventing mold and limiting toxicity/offgassing. With those parameters, ask the builder what the builder suggests as the most economical wall systems and construction methods. This will be heavily influenced by local factors such as labor & materials and the relationships the builder has with trusted subcontractors and suppliers.
Ask the builder for the suggested wall system, ask for references on other builds they have done that system. Then listen to the suggestions. Find out what the builder proposes for wall & ceiling R value, foundation system, the goal for airsealing (what ACH/50 number), and which material to minimize offgassing.
This has all been super helpful. I really appreciate it! Once our pretty good house is built, I will comment back on this thread to tell you what we did. My bestselling book will be entitled, “How to Build a House and Not Die.” 🥴