Issues with Insulated Concrete Forms (ICF)
Dr. Nabil Taha has over 27 years of structural engineering experience. Prior to opening his own engineering firm in Oregon in 1997, he was a Professor of Engineering at Northern Montana State University and at Oregon Institute of Technology. He has structural expertise in a wide range of building systems and can answer questions related to virtually any common building method. His focus is on green design and he is always willing to trying something new. Dr. Taha is dedicated to future sustainability through innovation; he creates solutions for beautiful sustainable and safe structures by melding old and new technologies. He loves a good challenge. He is Licensed in twenty three states and can design buildings and/or consult to assist with structural permitting in these states as well as internationally. As a prior College Professor, Dr. Taha is a teacher at heart. He loves to share his knowledge and offers educational seminars and trainings for the do-it-yourselfers and professionals alike. Dr. Taha's goal is to continue to grow and provide knowledge and services for those trying to make their dream project a reality. No project is too big or too small. For information about Dr. Nabil Taha and his engineering firm see www.structure1.com
Q: We are looking into a poured concrete house either insulated concrete forms or poured concrete into wall molds that is a new thing being promoted as better than concrete block and either we will build it or a contractor will. How does it compare to papercrete against high winds?
A: (Kelly) The Insulated concrete forms (ICF's) are very common, with several dozen manufacturers, but they are not very energy efficient. A better choice is to use some sort of "shotcrete sandwich panel", which puts the thermal mass inside the house where it can do some good. Either of these systems would probably stand up to hurricane force winds better than something made of papercrete, or standard wood-framed houses.
Comment: I noticed you compare Insulated Concrete Form R-value of 20 to 2x6 wall construction of R-20. Actually the studies show that 2x6 construction is rated at approx R-12 not the R-19 that is stamped on the fiberglass. Construction Technology Labs data shows that a wood frame structure of R-32 in Northern climates and R-55+ in Southern climates is required to compare to Insulated Concrete Form constriction. Your explanation of thermal mass working or not depending on where it is located in reference to the insulation was correct as far as we used to know. Recently the boys at ASHRAE have found that the mass does work - they just aren't sure why. Seems the argument now is whether there is 4, 5, 6, or even seven kinds of heat rather than the three we all grew up with. Just thought you would be interested in these updates. Feel free to contact me.
A: (Kelly) I agree that the whole evaluation of performance based on given R-values for materials can be misleading, and is really much more complex than it might seem. The performance is obviously affected both by climate and house design. I have talked to home-owners who live in ICF homes who swear by the inherent comfort, and others who say that the industry claims for insulation are way over-stated. In some climates, the balance of mass/insulation that is offered with ICF's might be just perfect, while in others it might leave something to be desired. I suspect that in climates that typically have either prolonged periods of extreme heat or extreme cold, that ICF houses perform less satisfactorily than houses that have substantial outer layers of insulation.
Q: I am considering building my own home and am looking at ICF's. I notice that you mentioned that the R factor is not as good as the industry say's. However, I wonder if it is still better than stick built insulated homes and can you put additional insulation which I guess eliminated one of the advantages time wise because they come insulated already. In any case with your experience does the R factor deter you from liking that form of building. Also the reason I liked it was because it looks fairly easy. I have some construction experience in framing. What's your opinion of the ease of use ICF's.
A: (Kelly) I have heard widely varying claims for R-values of ICF's, and it is hard to know who to believe. I think that it ultimately boils down to how well the particular design performs over the seasons. ICF homes are very tight with potential air infiltration, so this is an advantage, and they are quite easy to set up for a pour...this may be a good choice for you. From an environmental standpoint they use a lot of cement and other manufactured materials, and they don't perform as well as they would if all of that mass were inside the home.
Q: Do you feel that the Rastra is indeed an energy efficient building material? In a cold climate will not the cement transfer the cold from the footings causing for a less than efficient energy mass? Suggestions on building with Rastra?
A: (Kelly) The greenest part of Rastra is that it is made from recycled styrofoam, but it is basically an insulated concrete form, which is only moderately energy efficient. This type of construction does have a considerable amount of thermal mass, but it is unfortunately trapped within the styrofoam insulation, where it can't do its job as effectively as it should. Some home designs in some climates perform pretty well with this...but others don't.
Q: Wondering about your thoughts on Tech Block? Thinking of building a home using it. It appears to be environmentally sound, energy efficient, easy to work with and reasonably priced. I've compared it to others and because of the low amount of concrete, weight of blocks, price, it seems like it's far superior. What am I missing?
A: (Kelly) I looked over their website, and it does appear that this system would generally use less concrete and steel as compared to most other ICF's, so this would be good from an environmental point of view. Also they create a better insulated wall, which is also beneficial.
C: The newer and advanced ICF block systems on the market have brought construction time and cost to close parity with conventional frame construction. This is a huge factor that is resulting in phenomenal growth of ICF construction. This means a lot more energy efficient houses being built. Not by experimental "greenies" but by mainstream Joe Everyman. This is not small change -- we have an economically viable green building system that is entering the mainstream. Multiple production housing projects are underway currently across the country and these are enabled by delivering a system that is perceived as cost effective by the broad public.
Q: I would like to get Kelly to compare concrete masonry construction to icf construction. I would like an assessment of both single width and cavity wall systems using both construction methods.
A: The appropriateness of masonry wall systems vs. ICF wall systems (both hollow and solid) depends to some extent on the climate and the design of the building. In rather temperate climates, all of these systems would perform about the same. It is in the extremes of cold and hot climates that significant differences would be noticed. Without insulation, masonry walls transfer the outdoor temperature to the inside at a rate that depends on the thickness of the wall. With insulation that transfer can be slowed down considerable, depending on the R-value of the insulation. ICFs (insulated concrete forms) do provide an insulated break, on both sides of the concrete, so they are generally going to perform better than solid masonry in temperature extremes. Hollow core masonry will slow the transfer of heat some, but since there are usually thermal bridges of solid masonry in these wall systems, the pockets of voids don't provide much insulation. In a system where there are double walls, with a complete thermal break, then the performance is going to improve considerably, no matter what the walls are made of. The best situation would be with a solid masonry inner wall, and a more insulating outer wall, with a air gap (or insulating material) between them; that way the interior thermal mass can effectively moderate the interior temperatures.
Q: I am building a home in Kalamazoo, MI very shortly and am building as green as my budget will allow. The house will be a 2 story walkout with the MBR above the 3-car garage. So the house is pretty compact on other words. Do you recommend I use SIP's or ICF's? I'm pretty confused as to the very best for my area. I got to see a Polysteel addition going up this morning and it seemed very cool - but will it be too cold in the middle of January???
A: (Kelly) I think that you would ultimately have better control over the thermal characteristics of your home if you choose a highly insulating SIP system for the shell, use a good passive solar design for the home (see www.dreamgreenhomes.com for some ideas about this), and incorporate sufficient thermal mass material within the shell. The ICF manufacturers try to convince you that their system will incorporate both insulation and thermal mass, and to some extent this is true, but the technology compromises both aspects in the end.
Q: I'm looking for a product that: 1. as a skilled owner-builder I can stack myself, 2. will provide greatest insulation bang for the buck, and 3. I can apply stucco and plaster to directly, avoiding additional steps/cost. I'm building a 2200 sf home near the coast of Maine, two stories, about 500 sf of glazing to the south. Of AAC, Durisol, or Faswall, which of these technologies is best for this application?
A: I would say that all three of your choices provide moderately good insulation (although not nearly as good as strawbale or some earthbag structures) and would be quite durable and maintenance-free over time. All three can be plastered directly, as far as I know. The ICF's would certainly go up faster and be easier to assemble, however they often require concrete pumpers to fill the voids. I don't know about comparative costs; you'll have to pencil that out based on your local suppliers.
C: We are seriously thinking about the two ICFs you mentioned. They both have 12" blocks with mineral wool insulation inserts inside the block cores, meant to be set on the outside of the concrete, thus improving on the thermal mass issue you mentioned.
Q: Do you have any knowledge of the OmniCrete process being used in Florida. Basically it is 4" of AAC/vapor barrier/5.5" of concrete with rebar/vapor barrier/4" of ACC. It sounds better than ICF. Any opinions? www.omnicrete.com
For a passive solar house in a cold climate, which is better, SIP's or ICF's? If ICF's aren't good because they don't have thermal mass on the inside, are SIP's better, because they don't have thermal mass on the inside either, do they?
Q: I am preparing the design of my next build: a passive solar design, 2000 sf ranch in the Denver, CO area. The current plan is to use a conventional concrete foundation with 2 to 3" of EPS insulation on the ext. foundation to max. thermal mass and insulation, while keeping the costs for that component in line. After reading your comments, this seemed in line with your take on EPS ICF's.(?) I am leaning towards Faswall for the above grade exterior walls. Any thoughts? As you know Colorado has great solar aspects with a lot of sunny days, low humidity, and few temperature extremes...
A: (Kelly) Your foundation choice sounds good to me, for the reasons that you suggest, although ICF's used here would also be a good choice I think. Using Faswall ICFs for the above grade walls would not be my first choice, because they would compromise the availability of all that thermal mass on the inside because of the insulation they provide on both sides. A better choice might be shotcrete sandwich panels or Thermalwall or Endurablock or CFI.
Faswall's insulation is a mineral wool insert on the outside of the wall. I am hoping that their argument that they capture thermal mass with their arrangement holds true.
Well, that is what they say, but if you examine the layout of the ICF blocks and the insulation inserts, you can see that the concrete thermal mass is still isolated inside the Faswall block material. The question becomes "Is the basic block material insulating or not?" and my contention is that it is more insulation rather than true thermal mass, since it is composed of processed wood chips. But, even if it weren't insulating and were more of a thermal mass material, then there is still the problem of extensive thermal mass bridging from the outside to the inside of the wall, because their insulation only covers about two thirds of the wall space. They can't have it both ways! But, despite all of this, their system still likely performs quite well, even if it is not optimally.
Q: My husband and I are trying to plan our retirement home. This has been a 10 year research process and I'm getting really bogged down. We want something that is as energy efficient as possible, but we'd like to get the most "bang for our buck" in construction costs. Here are what we're looking for in our home: as energy efficient as possible - tornado/fire resistant - cost effective to build. I've narrowed it down to either underground, Rastra or SIPS construction. I think that the underground house would be the best bet, but I don't know if it's affordable. Which one would you guys do?
A: It sounds like you have done some good research in realizing that going underground will yield both energy efficiency and safety in a wide range of possible elemental dangers. Most insulated concrete forms such as Rastra can be used underground, at least for the walls. SIPs, on the other hand, are not generally used below grade. Completely earth-sheltered, underground homes often cost a bit more than their above ground counterparts, mainly because of the structural need to support all that weight on the roof. This additional cost can easily be justified over time in greater energy efficiency and in peace of mind. Go for it!
Q: My wife and I have just started the design process of our home in the Charleston, SC area. We are torn between conventional or ICF construction, what suggestions would you have for us to help us with our decision? I am also thinking of incorporating a solar system and possibly using a SIPS roofing system.
A: If you are comparing ICF and SIP construction with standard wood-frame building, I would advise the first for several reasons, especially in your climatic area, with the kind of storms you might need to endure. ICF walls are considerably more durable under practically any kind of adverse weather than wood-frame walls are.
Q: We are planning to build in sw ND. What is your advise on the use of Rastra blocks in this climate? We plan to have 3 of the outside walls partially earthbermed. One story home with cement radiant floor heat.
A: Rastra is an excellent Insulated Concrete Block. I do not see why it will not work in ND. Check with their agent in your area.
Comment: I am living in my second ICF home. We live in Arkansas where we have cold winters and hot summers. We moved into our new ICF home in December 2010. We experienced the coldest January and February on record. I am totally satisfied with the ICF construction for a number of reasons, and my satisfaction is based on fact not opinion. We moved into our home and found that the furnaces were not working. After some maintenance, they had forgotten to hook the furnace up. The outside temperature that first night was 14F. The inside temperature never got below 60F that night. Now, I call that green. ICF is ultra efficient. It is extremely strong which is comforting here in tornado country. As a matter of fact I was watching storm chasers on the weather channel where they had video of an ICF that took a direct hit from a tornado and the ICF walls were still standing afterwards. I would consider ICF extremely safe compared to any other construction under the same conditions. It's quiet and reduces the outside noises such as highway traffic. You have a window seat in every window and from my experience is reasonably priced. R value's are debateable for sure but all I can say is for the past ten years our utility bills for our ICF home has always been about half of what our neighbor's bills were, with them in timber homes. My only hope is that everyone could build an ICF home. It's second to none. Like grandpa used to say, no brag just fact.
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