Whole-House ICF vs. Zip Sheathing Integrated Insulation
Curious what people who have built high performance houses using both ZIP+external insulation and ICF construction feel about the two different construction methods? I know a lot of people are usually solid in one camp or another, but objectively after having built with both building methods what their thoughts are pros & cons of both?
We’re planning a new self-build and I am leaning towards ICF for the simplicity it offers as an all-in-one solution and seemingly needing less sub-trades. I know people say to expect ICF to be more expensive and take longer to build than if you’re doing a traditional minimum-code 2×6 framing with tyvek and cavity insulation but I wonder how much of that is true if you’re building a net-zero high performance home?
Appreciate if anyone could share their experience.
Thanks
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I have used ICFs for foundations and on several occasions my clients have been interested in using them for the whole house. I have not considered it because there are so many other ways to build that have less up-front carbon emissions. Proponents always exaggerate the thermal benefits.
The thermal benefit exaggeration is huge. Borst has an ICF thermal mass modified R-value calculator you can try, it's a bit finicky. At the end of the day, your true R value is what the foam is, R22 in most cases. The numbers that ICF manufacturers like to brag are from when the outdoor temperature crosses the indoor temperature within the 24 hour window. Your thermal mass modified R value in the summer could be very high if you get 60* nights and 90* days. Continuous R22 with a pretty solid (literally) air barrier is a decent bit better than a typical tract house, or most older homes with R13 haphazardly stuffed in the walls. Probably why the ICF community will exaggerate it so much, it's just a decent bit better than the norm.
The other thing to remember with ICF is that the foam is not your air/water/vapor barrier. The concrete is. The best assemblies will install/air seal the windows directly to the concrete, same with trusses or any other penetration. 10 years ago, the ICF manufacturers pooled money and did lots of testing on this, in order to come up with a uniform solution. When the easiest solution was the answer... They all came out with their EPS thermal bucks instead. The only thermal buck in the test had pretty bad results.
We are planning an owner with ICF for the similar reasons. Typically, ICF contractors can do flatwork, windows, framing, and roofing, so we can get a shell built with one sub, and you don't have much to worry about with finding contractors that are familiar with ICF from there. Our plan is Amvic's R30, so we are a bit beyond traditional ICF R values. Be careful, some of the brands have thicker concrete cores, and thinner EPS than the typical 2.5" per side. Because they are relying on the fictitiously high claims of ICF R values.
That's a really good point about benefit exaggeration. Adding heat capacity to a building only has an effect in the "shoulder" seasons -- days when you need both heating and cooling in the same day. Additional heat capacity tends to buffer temperature swings from day to night. The problems with putting too much stock into that effect are:
1. Conventionally constructed houses aren't lacking in heat capacity
2. That's the time of year when energy needs for heating and cooling are their lowest
3. You can get the same effect by insulating the house, and the insulation provides benefit year-round.
If the material you choose to add heat capacity is concrete, there is an additional drawback that its production has significant negative environmental and climate impacts.
In this post, starting at comment #17 I do a detailed model of the effect of adding heat capacity to a house: https://www.greenbuildingadvisor.com/question/cooling-a-home-with-no-ac
It's worth a read.
I did read through that, I think it is a great demonstration of how it impacts your house. For cooling, shifting the peak cooling to the evening could be pretty beneficial as now you could simply open windows or have your ERV bringing in cooler exterior air. But your point remains, insulation would be better year round.
The dampened curve is also probably why ICF manufactures love to point out how their HVAC systems can be smaller. A flatter curve means you don't need to design for as large of a peak, but overall energy usage would be the same throughout a 24 hour period. Concrete isn't immune to the pesky laws of thermodynamics.
In your thermal mass estimate, I bet an ICF house is closer to 3x the weight of a conventional house, with most of the difference in the walls. For an exterior wall, a 6" core concrete is about 75lbs sqft (150lbs/ft^3), while a 2x6 wall assembly is around 12lbs sqft. On my simple shaped ~2,000sqft house plan, that adds around 150,000 lbs to the exterior walls.
I justify it to myself by trying to eliminate the basement, so I'm moving my concrete up essentially... Reality is I do know I am doing a bit of a disservice to the environment putting this much concrete in my walls, and it would take planting a lot of Oak Trees to offset it. Living in the Midwest and having too many nearby tornadoes, I am a believer in the strength portion of ICF. You do get an insurance discount for this as well. I'm not sure I'd be comfortable in a conventional house without a basement here in the midwest. There was a tornado that knocked a freight train off the tracks in my hometown!
I have seen people very happy with both types of houses, high performance standard frame and ICF. I think which route is better will depend on the individual.
I will say for multi family type housing the ICF party walls make great fire and sound separations, both because of the material properties and also because the sub trades cannot easily penetrate the walls and must come up with other solutions.
In an area prone to tornadoes I would lean towards ICF.
It has been my experience that concrete guy do not suffer fools well.
DIY general contractor doing his very first concrete pour of his life has a very high fool potential add a pumper truck and Styrofoam forms to the mix and you have the making for three stooges’ production.
I am just saying with a stick framed house you can work at your own pace and any problem can be corrected easily not so much when you have 3 concrete truck backed up and wanting to unload in the next 10 minutes.
Walta
Thanks Walta. Just to clarify I'm not planning on doing any of the work myself. By self-build I mean I'm the GC and hiring sub contractors directly vs a builder to manage the project. It's fairly common in my area.
Thanks everyone. All good info to considered. For the 2 storey home we're planning we've drawn up our plans with the assumption that we're going with Anvic R30 ICF to the rafters. But we're still at the stage where I can change to do ICF for the basement only and a ZIP/External insulation for above grade.
Some of the draw backs is the extra thick walls with R30. Also requires extra support where our design has some 2nd storey walls not lining up with the 1st floor. I'm still leaning towards ICF for the simplicity of getting the shell built with one sub-trade including footing & foundation. We've self-built 2 homes in the past where we hire all the sub-trades which is why I may be more partial to simplifying things.
The aim of this new house is that it will be our "forever home" so I'd like to build a really high performance net-zero home. I was looking into doing ZIP with external insulation but by the time I factor in all the extra details in air sealing and boxing out for external insulation (our facade will be traditional brick) it seemed very difficult to trust everything to sub contractors to get all the details right without completely micro managing it. I'm also not sure how much cheaper it would actually be even considering the cost of ICF. For what it's worth I'm in Ontario climate zone 6 with very humid summers and cold winters.
There are some ICF buildings in my area that I have been involved with recently that have achieved BC Energy Step Code 5, which is the highest rating of our provincial standard for energy efficient buildings. The detailing for air tightness is less involved with the ICF system than with standard framing and a crew without much experience in high performance building came out with some very air tight buildings.
There is an updated envelope guide from BC Housing (you will find it with a google search) that has many pages of details for ICF construction, it is a very good reference.
sraisic,
Two big disadvantages of ICF I see are that during construction you need to be bang on and any errors - out of plumb, wrong RO for windows and doors - are very hard to correct. ICF buildings are also very hard to modify or renovate over time.
You may find this worth a look: https://nextstartech.com/shop/custom.aspx/icf-foundation-problems/36/
Thanks. Those are good points I'm considering. I think getting the details right and planning ahead any openings and/or sleeves will be critical. One positive point I heard is that an advantage of ICF is that it does force you to really plan ahead. Provided you get it right of course.
Lot of this comes down to what trades are available and what they are familiar with. Before getting too far down the road, I would get pricing. Some details are different on ICF, for example hanging joists, so account for these as well. Don't forget to include shoring/bracing as well.
House shell should be one of the lower cost items on your build, if this is not the case, I would re-evaluate.
P.S. Even if your electrician/plumber has done it before, wiring/plumbing ICF is not straight forward, so I would have an extra line item for that as well.
Thanks
Do the math in most climates R30 walls a silly expensive and never save enough energy to recover their costs in fuel saving especially if you are unlikely to stay in the house over 20 years. Since this is your third dream house that seems unlikely.
Walta
If talking ICF, at least by me, Amvic R30 is around $0.50/sqft more than the R22. Pretty good deal considering the labor is identical. If anything, lower risk of blow out with the thicker foam too.
At some point, I would hope that in the US it catches on that a well built house has value to a potential buyer, so even if you end up moving again before you pay off from an energy cost, you can recoup some costs.
"in most climates R30 walls a silly expensive"
He isn't in most climates, he is building in Ontario. Climate zone 6.
"...you are unlikely to stay in the house over 20 years. Since this is your third dream house that seems unlikely. "
Where did you get from his posts that this is his third "dream house"?
Also it's not are 3rd dream house. We never planned on staying in the first two for longer than a few years while I was able to use the experience to learn what I wanted and didn't want in our final home. This last one will definitely be our last...by order of my wife who won't move anymore lol. Our kids are in grade 1 and pre-school so we intend on planting our roots in this house.
It's an intangible, but a well-insulated and well-sealed house is just more comfortable. Also quieter and cleaner.
Those things may not be appreciated by potential buyers and so may not factor into resale value. But there's more to it than just lower utility bills.
I think we can safely assume that as energy prices continue to rise, energy efficiency will hold more value in the real estate market. Just like filling the tank on a v8 truck is no longer fun, heating a large leaky house is starting to hurt.
I agree with Michael (comment 1). Let's be honest about ICF construction. It's not a green building technique because of the exorbitant injection of CO2 into the atmosphere with that type of construction. I get tired of the what-aboutism people use to make excuses for it. Sure, you can make an ICF home comfortable and have low energy consumption over its lifetime. Sure, a basement is also bad. Here's an idea: Don't build basements either. Why use construction techniques that use excessive concrete if conventional construction can be made to have much lower up front CO2 cost and equally low energy operating costs of ICF homes through their lifetime. Also, up front CO2 injection into the atmosphere from concrete is far more important than is low energy use during a home's lifespan.
The only legitimate reason I can see to use ICF is in tornado alley in the Midwest. That's because having to rebuild is the most energy intensive predicament you can be in. I say don't use ICF except for that reason. Implying ICF is green just because it can be made to have low energy consumption over its lifetime is incorrect. It's not.
I've built both with ICF and wood frame. I believe ICF is the way to go in the desert southwest (Zone 4B) and will build with ICF for my future house. Main reasons: 1 - Fire resistance. Living in a wildfire area, the 6-8 inch thick concrete walls provide better fire/heat resistance than wood frame walls. 15-30 minutes (wood) vs 4 hours (ICF concrete). Of course, installing a steel roof completes the enclosure.
2 - Pest/termite resistance. Every wood home in my area eventually has termite infestations in the structural walls. With ICF, the EPS foam provides no nutrition for termites and even if they do get into the EPS foam, the concrete core provides the structural so the foam being damaged will not affect anything. Unlike wood frame, which if not addressed, will cause the walls to sag and eventually fail. In addition, every wood frame home in my area gets scorpions, mice and even rats infesting the wood wall cavities. Scorpions will easily get through the weep screed, crawl into the wood walls, and come out through the baseboards, light fixtures, electrical outlets or any gap in the drywall. This is not possible with ICF walls. Not having scorpions in my house is alone worth the price of ICF :) Mice and rats will chew threw wood OSB & studs and make their way into walls and attics.
3 - Sound/wind protection. The ICF walls are rated for 200 mph winds. Hopefully I never see that type of wind but in high wind events there is dead silence and no wall movement or wall noise. My wood frame home walls would creak, pop, flex, when we would experience 60+ mph winds. ICF walls have a STC rating of 50+
4 - Energy efficiency. Yes, most ICF walls will have a true R-23 rating. There is almost zero thermal bridging in an ICF wall, unlike wood frame which has a thermal bridge each time there is a wood wall stud present, especially around doors and windows which is stud intensive with 2x's stacked on each other or large wood headers. Living in the desert southwest, I experience vast diurnal temp swings. It can be 95F in the daytime and then 55-60F at night. ICF does very well in these conditions. In these conditions, ICF will perform like a R-50 wall. Now, it is also true, if you live in an area that does NOT have vast diurnal swings, then the ICF wall will not perform like this and you will see a steady state R-23 wall.
I am NOT knocking wood frame. In climate zones that don't experience what one experiences in the desert southwest, wood frame is a great choice and one can attain high R-Values with a wood frame wall. I believe building methods are zone/climate specific and there is no one size fits all approach.
To points 1 and 2: I would think the foam would melt pretty quickly in a fire, and I know that while termites don't eat foam they tunnel through it readily. Does removing the foam compromise the strength of the concrete?
Once the concrete is poured and cured, the EPS provides no strength to the wall assembly. The foam is basically a form for the concrete. Once the concrete is poured and cured, the foam can be removed if you wanted to but you would lose R-Value. The ICF EPS is basically a stay-in-place form.
jackofalltrades777,
I don't know much about building in hot climates, but Martin suggests CMUs with exterior insulation. Does that make as much sense as ICFs?
https://www.greenbuildingadvisor.com/article/designing-a-house-for-a-hot-climate
CMU's with exterior foam would basically double the cost compared to an ICF wall. The labor, manpower & time involved in CMU's vs ICF is not even on the same playing field. 1 or 2 people can easily stack ICF walls and do so very quickly. Strength wise, ICF wins hands down to CMU. A 6 or 8" thick monolithic ICF wall is drastically stronger than a grouted CMU wall. They've tested projectiles as found in tornado, shooting a 2x into a CMU vs ICF wall and ICF wall would not let the 2x penetrate the wall while the CMU wall broke and allowed penetration.