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.
Best regards, Rick Hansen, Reddi-Form ICF LLC

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 HAVE DEVELOPED A SITE-PRODUCED SOY-BASED POLYURETHANE INSULATED CONCRETE FORM. I WANT TO DEVELOP A HYBRID BUILDING SYSTEM THAT UTILIZES THE SOY ICF (POST&BEAM) WITH PAPERCRETE AS INFILL BETWEEN THE POSTS. MORE INFO MAY BE OBTAINED AT WWW.EMEGABUILD.COM.

A: (Kelly)I looked over the information at your website, and it all looks pretty interesting. ICF's made with the soy-based foam would certainly be more green than the typical EPS products. Your idea of just using the ICF's for creating solid post&beam support, and then infilling with something that provides better insulation seems like a good idea to me.

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.

A: (Kelly) I really appreciate many aspects of ICF construction, including the economy that you mention. Also the durability is unquestionable, along with all of the trees that it saves. But in evaluating "greenness" in terms of embodied energy it does not measure up well in comparison to most of the other more natural technologies mentioned at greenhomebuilding.com.

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

Q: I hadn't heard of Omnicrete until now, and looking over their specs and all, I would agree with you that their system would be superior to most ICF systems in several ways: more durable and fireproof; can be finished directly both inside and outside without other sheathing materials. I distrust their R-value assignments, but I suspect that the system would perform well. Again, you still don't have any internal thermal mass inherent in the system.

Q: 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?

A: (Kelly) You are right that SIPs don't have any thermal mass associated with them, but they generally provide better insulation (depending on their thickness) and don't require all of that cement and steel...and thermal mass can always be added to the interior of any house in various ways.