New Build – Off Grid Home in Climate Zone 7 Northern Ontario – ICF or Bonfiglioli Wall?
Hello!
My husband and I have just acquired land in Northern Ontario, and we are working with a passive house certified builder and home designer. We have drawings for a 1500 square foot home for our family of 6 and we have to be off grid where we are building.
Our builder has suggested building with an ICF basement and then the bonfiglioli wall assembly above ground for the main floor. There will not be any second storey. The house has taken some of the design ideas of the “pretty good house” and some passive house design with south facing windows. We are heating with a woodstove on the main floor and will have some sort of erv system.
We know of two other couples who have their houses totally constructed with ICF and we really liked how cool the house stayed in the middle of the heat here in the summer. We can get 40 degrees Celsius in the summer and -40 degrees Celsius in the winter.
My question to this community is would it just be more efficient to build using ICF from the basement all the way to the roof line, or ICF for the basement and bonfig for the main floor? Thank you in advance for the helpful advice.
** Edited to add:
-The builder we are working with has only used the bonfig wall assembly in some remodels, never with new construction.
-When I say efficient, I’m referring to cost, ease of construction, and also heating and cooling demands in a house (since we will be off grid)
-We are planning to build in 2025, and being in Canada with the possibility of the tariffs coming from the US, I’m concerned about how that would affect the cost of building materials
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Replies
What would be the R-Value of the ICF?
I don't know the answer to that question. I always assumed that the thermal mass of the concrete was in its own way on par to a high R something wall?
Well, the concrete has an R-value depending on how thick it is but it will only be a small portion of the entire wall's R-value. The majority of the R-value comes from the foam formwork. Personally, I'd compare the R-value, cost, aesthetics, and environmental impact and then make a decision based on all those combined however you weight each factor. It sounds like the general consensus is that that other stick frame type walls are better than the bonfiglioli wall. You might discuss with your builder other options to get a high R-value that may be more cost effective or environmentally friendly.
Usually, ICF manufacturers inflate their advertised R-value by claiming that the "thermal mass" gives them a boost above and beyond the simple R-value of the foam. That is simply bogus. It's sort of like how the radiant barrier manufacturers claim they can increase R-value with a thin layer of foil or a thin bubble-wrap product around ductwork. Concrete is a very poor insulator, and allows a lot of heat to move through it. Usually, it is cheaper to build a stud-framed wall. It depends on the market though. For a below-grade basement the cost may not be too much extra to go with ICF over a poured concrete wall. I would be surprised if it was cheaper above grade though. The benefits of a stud-framed wall is that you can always apply exterior insulation and you can get higher R-value per inch than the EPS or GPS foam used by the ICF manufacturers. Wood is usually cheaper than concrete, is a better insulator than concrete, and is way more environmentally friendly if you're inclined to that sort of thing.
Why does the IECC allow for a lower R-value wall when the wall is a mass wall like concrete?
https://codes.iccsafe.org/content/IECC2021P2/chapter-4-re-residential-energy-efficiency#IECC2021P2_RE_Ch04_SecR402
Because lobbyist...
High heat capacity walls can be made to work decently, but they are rarely done correctly. It usually ends up overheating the home in the late afternoon and underheating the home in the early morning. It's pretty much always better to take the increased cost of ICF and apply it to better R-value assemblies.
Who would lobby for this, and why?
Plenty of trade groups exist with the primary purpose of maintaining their members' interest in governmental standards. For example, the National Concrete Masonry Association (NCMA), and the Concrete Masonry & Hardscapes Association (CMHA) when it comes to concrete. But also the Insulating Concrete Forms Manufacturers Association (ICF-MA) for ICF's and the Log and Timber Homes Council (part of NAHB) for timber frame homes. I don't have any way of knowing which group(s) were responsible for getting section R402.2.5 added to the IECC.
The comments on this article may be helpful:
https://www.greenbuildingadvisor.com/article/mass-walls-increase-insulation-value
The benefits are very region-dependent. A lot of climates would be better off with highly insulated stud-framed walls.
I'll offer a slightly different take.
The IECC does try to be as sensible as possible, in particular they try to be sensitive to cost-benefit analysis.
When they talk about "mass walls" (a term I hate) they really mean foundation walls. These tend to be more difficult to insulate than wood frame walls, so the cost-effective insulation level tends to be lower. It really has nothing to do with science.
"efficient" is an interesting word ...
Do you mean to construct or thermally?
Both. This home is where we hope to spend the rest of our lives, and we are only getting older. Being off grid and heating with our woodstove, we want the home to be efficient and also built to last as we don't want to work hard to keep our house warm and cool at different times of the year. Is ICF more efficient because of its thermal mass? Is ICF more efficient in regard to cost (assuming the 25% tariff coming our way to Canada and affecting the cost of building supplies)?
bl_al,
If you decide to go with a Bonfiglioli wall I'd suggest a possible modification.
The technique is usually limited to people building their own houses because it is so labour-intensive. If you move the foam strips to the exterior under the sheathing, you don't need to cover them with plywood strips the way you do on the interior. It also allows you to insulate the exterior of your rim-joists with foam board.
Bonfiglioli walls can be a good solution for improving the efficiency of existing walls. I have modeled them and considered them for projects several times, but I just don't think they make sense for new construction, when there are so many other options that have a bigger payoff for the effort.
I never see a reason to build with ICFs above grade, when there are so many other ways to build that don't use the two most climate-damaging materials typically used in construction. My personal favorite in most cases is a double-stud wall with cellulose insulation, which can easily outperform an ICF wall, using low-carbon materials.
I design homes in Maine, with a similar swing in temperature, though usually closer to -30°C to 35°C.
Thank you for your response, can you elaborate on how the double stud wall can outperform an ICF wall? Our builder has only ever used the bonfig wall assembly in remodels that he has done, and not new construction, which has led me to have slightly cold feet with his idea. I just want to make sure we are doing the right thing for longevity, efficiency, cost, and time.
Here are a couple of articles by builder friends I have worked with:
https://www.greenbuildingadvisor.com/article/a-case-for-double-stud-walls
https://www.greenbuildingadvisor.com/article/how-to-get-a-double-stud-wall-right
In short, you can make the walls any depth; I usually use roughly 12" walls for a whole-wall value of around R-40, or sometimes I use thinner double stud walls and get closer to R-30.
ICFs use thermal mass as a selling point, but that's far less effective than people think, and adding more insulation is almost always a better value than adding more mass.
ICFs use airtightness as a selling point. My double-stud projects routinely reach 1.0 ACH50, often closer to 0.5 ACH50 and a couple are around 0.1 ACH50. In other words, incredibly airtight. And that's without overly complicated or expensive detailing. I have not heard of ICF buildings routinely reaching those super-low airtightness values, though I'm sure it's happened.
ICFs use storm resistance as a selling point. Concrete and foam are certainly durable, but wood-framed homes built to at least current codes should fair very well, and if you want more protection, this is a good program: https://fortifiedhome.org/.
Almost all homes will be renovated or added onto at some point, and both are easier with wood-framed construction.
Wood framing and cellulose (or wood fiber) are renewable resources and have small carbon footprints. Concrete is the single largest CO2 emitter in the world, responsible for as much as 10% of global emissions. Every pound of Portland cement used represents over a pound of CO2 emissions.
Thank you Mike for your response and the articles. I am not a paid member to the site so I cannot access the full article but I was able to glean quite a bit of information from what I could read and also the comments. I do get a bit overwhelmed with all of the jargon that I am not accustomed to, so I am trying to process what all of this means. However I greatly appreciate how you laid out your response comparing ICF to wood framing. It has helped ease some of the concerns I had with the idea of the bonfig wall on our main floor.
So in your opinion, what would be the best way to talk to the contractor about the type of wall assembly when he is the one with the experience and knowledge and I am just the homeowner?
If you're not opposed to EPS, there is an interesting "SIP type" of panel company in Western Canada called Greenstone that might be of interest ...
https://gsbp.ca/what-are-ice-panels/
Like others have suggested, the Bonfiglioli approach isn't necessarily the easiest way to get a high-performance wood-framed wall, but every builder has their own opinion. If your builder has experience with it and likes it, there's no reason not to use it. As with continuous exterior insulation, the thermal break provides a significant improvement over a plain stud wall. For really high R-values though, nothing beats the cost-effectiveness of a thick double-stud wall filled with cellulose.
For a home heated primarily by a wood stove, thermal mass can offer some benefit in moderating the heat output of the stove. But it will provide the most benefit when it is completely inside, not buried behind a couple inches of foam. Better options might be a masonry hearth and wall protection, or a concrete floor topping.
If having to be off-grid means that you are far from a ready-mix plant, that will add to the cost of an ICF wall.
My question is have you fully drunken the passive house Kool Aid and gotten to the point that logic and reason have become optional?
The passive house equations do not have any dollar signs in them. In short cost is irrelevant in the passive house system. The only thing that matters is BTUs per square meter.
Do you really need the approval of others so much that you will pay thousands of dollars to win it with a certificate.
Consider building a “pretty good house”
https://www.greenbuildingadvisor.com/collection/the-pretty-good-house
ICF has been around for 40 years now it has not dominated the market because it is not the low-cost way to build a wall of the same R value.
Big south facing windows are an energy negative generally. If you have a great view by all means, put in some windows up 20% of the walls area.
Putting a wood stove in a tight energy efficient home is like mixing oil and water. I am not saying it can’t be done just that it will not be easy and you need to plan ahead.
Consider using a BEopt model of your home to make your choices.
https://www.nrel.gov/buildings/beopt.html
16 BEopt training videos
https://www.youtube.com/watch?v=GdMYCuwp0AY&list=PLHC0xDtkdjgec8QhVt7exJY3tpSLEFk-d
Walta