http://www.forms.org/images/cmsIT/f...ect(1).pdf

I'm adding this topic because it keeps coming up and taking other threads off course. 

Now that the best performing schools in the US are predominately mass wall systems (see ASHRAE K12 50% solution) - with the best performing school currently utilizing an ICF wall system and operating at 17 kBTU/sqft per year --   I believe this has been put to bed.   Thermal mass is real and the newest charts even show that mass wall (Heat Capacity > 7 BTU/sqft F ---  with R-value X beats a low mass wall with R-value somewhat more than X in all climate zones.  

ORNL states that mass walls performs slightly better with their mass to the inside whereas ICF has it's mass in the middle.   I am not entirely convinced this more immeditate or direct interaction of the mass with the interior might not be better sometimes or in some climates than in others.  Nevertheless, it very well may be true.  However, to equal a typical 6" ICF wall this equivalent wall system is going to have to have an R-20 - R22 exterior insulation with 6" of solid interior unobstructed concrete -- thus matching the R-value and heat capacity of a 6" ICF wall.    Thanks in advance for your thoughts.  Regards.

Posted By Lee Dodge on 22 Jan 2012 05:37 PM
The link that you provided to the ICF manufacturers association restated conclusions from the report by VanderWerf (reference 2) that was performed for the Portland Cement Association. In that report comparisons are made for energy use by ICF homes and wood frame homes in similar climates with similar floor areas, all of relatively new construction -- new whenever the undated report was published. There apparently was no effort to match wall insulation R-values! So a house with 2x4 walls with fiberglass that has an R-value of R-11 uses more heating and coolng energy than an ICF house with R-22 walls. Is this conclusion surprising or even interesting?

A more interesting comparison would be to use a fixed budget to spend on a house of the same floor area, and see if the money is better spent on ICF construction or wood frame with a very high R-value, which would be possible since there is a considerable price premium for ICF construction, much of that due to the requirement to use rigid foam rather than cellulose of fiberglass, which are much cheaper per unit R-value. Perhaps you could perform some calculations with BEOpt which has prices for different construction and report back to the group on equal cost houses.

After a brief glance, about the only thing that I saw of interest in the VanderWerf report was Figures 1 and 2 and the comments made relative to those figures. Those figures appear to undermine the thermal mass effect advantage for ICF.

Perhaps this paragraph: "There are theoretical reasons to expect that the fractional savings in energy might be different in different climates.  For example, the thermal mass effect should be more pronounced in moderate or warm climates because the outdoor temperature there more often fluctuates about the thermostat set point. Thus fractional heating savings might be greater."

Regarding BEOpt that might be a better task for you since most of my data is emperical.   Regarding cot of ICF:  It usually it costs about 5%-7% more (for the entire cost of the dwelling) for ICF over conventional -- e.g. a 200K conventional house will run 210K-214K after reducing reducing AC tonnage and pulling out the cost of labor and materials for the external envelope and applying them toward the ICF.  Naturally, this percentage value goes up with smaller houses and down with very high end houses with finer finish out.   In Texas, ICF homes usually go from $10 to $12 per gross square foot of wall turnkey.  Complex structures with lots of radius walls etc. or 350 mph rated structures etc.  will be higher.  By comparison, here we usually find conventional construction is about $4-$5 per square foot of external wall.  New code -- eg. IECC 2009 and the forthcomming IECC 2012 are going to generally make conventional construction more expensive and will generally not impact ICF much at all.   

As you know, the reasons to go ICF typically vary from person to person.   When comparing ICF to conventional, you'll need to upgrade a bit on what considered conventional here to reach the thermal performance of ICF.  I would say there are just as many folks that prefer the safety of a concrete home or the STC (sound transmission characteristics) of an ICF home -- perhaps they are building near a railroad or a highway.   Occasionally, and more recently, I might add, they are looking for a three or four hour fire rating because their previous home burned down.  

Based on the many homes I've been involved with I believe in general it's as good as construction gets for the money.  As soon as you start trying to get similar strength or fire resistance or STC "and" energy efficiency out of conventional construction I belive you are going to pay more for it than for ICF.   Regards.

Posted By lzerarc on 23 Jan 2012 10:50 AM
TX-
I fail to see what that pdf proves. It claims what we already know. We know mass in buildings, if used correctly, can affect the performance positively. What we do not know, and have yet to see any proof (besides the "old" reports that actually disproves it...) that the sandwich mass in ICF has the mass effect ICFers (you) claim, especially in heating dominate areas which is a great deal of the US. Further more, the ICF case study in the school (which you have to agree the requirements and performance of a school vary greatly compared to homes) does have a high performance level. However how are you sure that the pure insulated levels of the ICF are not playing into it compared to externally insulated mass walls? Code in our area only requires an r13 for CI on mass walls. So that is what we put. Of course if we use an r24 ICF wall it will perform better then an r15 mass wall. Same with frame walls. I do not think anyone on here will disagree with an ICF beating a frame wall with batt or blown insulation. CI and air tightness are playing into it big time, however the thermal mass?
What I want to see is a compared wall assembly built to similar thermal breaks, insulation levels and air tightness of a typical higher cost ICF wall. Better yet I would want to see a double stud r40 wall compared to a typical r24 ICF wall (who many ICFers claim pushing r40s due to the "mass effect"). I already know the results cause we have ones around my area to compare.

Posted By lzerarc on 23 Jan 2012 10:50 AM
TX- 
However how are you sure that the pure insulated levels of the ICF are not playing into it compared to externally insulated mass walls?

Posted By lzerarc on 23 Jan 2012 12:44 PM
We could debate the wall make up of the double stud, compare framing factors, prove its not really r40, blah blah blah. On paper, we can look at numbers all we want to. It doesn't have to be double stud. It can be any super insulated shell vs ICF. SIPs, PERSIST, etc. What most of us are suggesting is numbers are not doing the talking any longer. There needs to be more apples to apples studies comparing performances. ICF companies compare their shell to 2x4 or 2x6 with batts. There is not a single person on this forum that would disagree with ICF being much higher performance compared to those. My point was how does it compare to super insulated homes that cost less? Why are they not comparing ICF to these? Or in some cases even above code min. structures. In my area a 2x6 with batts doesn't meet IECC anymore without CI.

IZ - but everyone is comparing the extra cost of ICF to conventional homes NOT to other SI home i.e. 10 to 15% more. Bob

Around me there is a new home that was recently finished using the double stud detail we did. So far the performance can not be touched by other ICF homes we are comparing it too, most of which do have spray foam ceilings. It is a larger home with close to half the heating cost in the last month of a smaller ICF home we are comparing it too. Sure, there are various variables, but the fact is SI wood structures can and do work, very well. If not why would PH be using these construction methods and rarely full shell ICF? (most do us ICF on the basement).

IZ - I was involved with a number of the early R2000 home in the 80's in the Calgary Alberta area. Not one of these comes anywhere near the efficiency today that they did when they were built. Why? Primarily because they were built from wood. No matter how you seal it, wood will respond to moisture and temperature. As it changes shape and moves it will eventually degrade the best airseal. Once the airseal is gone, infiltration takes over as the limiting state and all the R becomes less meaningful. Bob

Not knocking ICF, it is a very good, strong structure with many great attributes about it that has me thinking long and hard about it as a good option. However it gets roped into the high efficient category far to often. For the cost, and the goal of high efficiency, your dollar is spent better elsewhere IMO. Wind, storm, fire, sound? ICF all the way if those are your goals. To be honest if budget was 0 concern, I would do a full shell ICF and add another 2-4" of EPS on the exterior.

Posted By Chris Johnson on 23 Jan 2012 09:29 PM
The R-50 as you know is a false number.

The ICF industry needs to get together and build TWO identically sized homes next to each other. Both with identical HVAC equipment and identical temperature settings. The one home utilizing ICF and the other 2x6 wood frame with foam or cellulose insulation and then 2" of EPS on the exterior. Put sensors and monitors throughout the home and record the data for an entire year. Then publish the results. This would settle it once and for all. Well, at least for 90% of the people it would.

Didn't they already do this at Oakridge National Labs?