I have read a lot of information, but I suffer some confusion. Please help me understand why ICF's are so popular. I completely believe in the value of thermal mass. But ICF has a layer of insulation on the interior, so how does the concrete store heat? As I understand it, ICF's need to be filled with concrete. An ICF block costs over $12, a CMU about $1.25. Insulation (3" of foam board, R20, about $4.50/block) Both have to have exterior siding/UV protection? ICF's need interior drywall or fire protection? Dry-stack block with SBC (surface bonding concrete) does not. CMU does not handle electrical wiring very conveniently. How does ICF differ? I admit to a current bias towards dry-stack CMU or even better, shotcrete domes. But I'm open to understanding why everyone here thinks of ICF first.

Posted By McFish on 19 Mar 2011 01:47 PM
I have read a lot of information, but I suffer some confusion. Please help me understand why ICF's are so popular. I completely believe in the value of thermal mass. But ICF has a layer of insulation on the interior, so how does the concrete store heat? As I understand it, ICF's need to be filled with concrete. An ICF block costs over $12, a CMU about $1.25. Insulation (3" of foam board, R20, about $4.50/block) Both have to have exterior siding/UV protection? ICF's need interior drywall or fire protection? Dry-stack block with SBC (surface bonding concrete) does not. CMU does not handle electrical wiring very conveniently. How does ICF differ? I admit to a current bias towards dry-stack CMU or even better, shotcrete domes. But I'm open to understanding why everyone here thinks of ICF first.

McFish,

First I must admit (as well) that I have a definate bias toward ICF.

That said, ICFs aren't as popular today as they are going to be tomorrow.   In fact CMU is still a bit more popular among most architects.  Things are changing pretty fast thought with IECC (new code) being adopted in most states (e.g. foam inserts for CMU will no longer count toward R-value). 

CMU also has thermal mass just not as much as ICF.

Electrical requires cutting foam for the ICF.

ICF like CMU have thermal capacitance the only main difference is that ICFs (because they are insulated on both sides) are much slower to interact with the environment or warm up or cool down -- a good thing in most climates.   

ICF block is sold by square foot -- the block I prefer is a little over $3.00 per square foot.   Some ICFs talk about block pricing and charge different amounts for corners or Ts or etc. and I believe that doesn't help move the industry forward as fast as clear communication (but that's off track here).   A CMU block is generally about 88% of a square foot or about $1.40 (based on your $1.25).   Regarding the 3" of foam -- are you talking about per square foot?  

When I compare these systems I try to use installed prices for clarity.    In Texas, it costs about about the same to install (labor and materials) a square foot of ICF and a square foot of CMU.   Until the new code requiring CMU to be more energy efficient the advantage was slightly in favor of the CMU.  Now it is in favor of ICF.    Since ICF is significantly stronger sometimes you can reduce or eliminate some perimiter steel etc. 

You might check out this article from ICF Builder magazine.   Regards.


http://www.icfmag.com/articles/feat...r_cmu.html

Well put Texas

Here's a good article from ICF Builder Magazine that addresses ICF vs. CMU
http://www.icfmag.com/articles/features/icf_over_cmu.html

Oops. I didn't see the same link above

As far as I can tell, a typical ICF negates some of the benefit of thermal mass. But then thermal mass only helps when the outdoor temperature swings above and below a steady state indoor temp.

http://www.buildinggreen.com/auth/article.cfm/1998/4/1/Thermal-Mass-and-R-value-Making-Sense-of-a-Confusing-Issue/

Tell me we don't have to do this again, Texas ICF. To refresh your memory, thermal mass does its best work in 24-hour periods, by buffering daytime heat and nighttime cold. Common sense says it works better with the insulation on the outside and the mass exposed to the interior. So do the building scientists at Oak Ridge National Laboratory. http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/potential.html

Your claim that ICF's slower response is "a good thing in most climates" is misleading at best. The article's claim that cmu needs 5 inches of foam to be comparable to ICF is unsupported, and is almost surely crap.

Interesting article. Interior mass or concrete/insulation/concrete perform somewhat better than external mass or ICF.

toddm, Do you really believe that CMU provides some R value contribution? The CMU contribution is similar to the contribution of the concrete inside the ICF - very small. The reason you need the 5 inches of continuous foam to get similar thermal performance out of a CMU is because your typical ICF has 5 inches of continuous foam and your typical CMU has none.

Why do you suppose the new International Energy and Conservation Code (IECC) does not allow foam inserts in CMU to count toward R-value? Why must it have a full continuous layer of foam to meet code? Because a CMU block is a conductor.

Regarding ORNL:
As jonr said "Interesting, around 8% savings with mass on the inside, 7% in the middle and 6% on the outside. Small differences. " These are small differences and yes, mass to the inside is best. However, the small print that most don't notice (particularly those who misquote ORNL) is that each of these wall systems tested have the same R-value and the same thermal mass --how else would one isolate the value of the thermal mass for a thermal mass report? What does this mean? If your typical ICF has 2 1/2 inches of foam on each side and six inches of concrete in the middle then your comparable system with interior mass will have 5 inches of foam to the exterior and six inches of concrete to the interior. I'm not saying that this math model system can't be built or doens't exist but please don't try to tell me that CMU is remotely in the same ball park or comparable in any way. A CMU block has significantly less thermal capacitance (mass) and almost no R-value.

If you are looking at blocks use AAC, much better in every aspect except probably price.

If you are looking at blocks use AAC, much better in every aspect except probably price.

TexasICF:
Exterior foam/interior mass saves more energy than ICF, all things being equal.
Therefore, external foam/interior mass needs LESS foam than ICF to achieve comparable performance.

In a dry climate with wide swings in daily temperature, it could be a lot less foam. In the ORNL study above, interior mass in Bakersfield, CA cut whole building energy use by 18 percent while ICF cut it by not quite 10 percent. If you look at Fig 8, you'll see that ICF's performance in Bakersfield barely changed as ORNL reduced its insulation from R25 to R5 (i.e., that the dynamic benefit of thermal mass increased as R value decreased to the point that energy savings was almost a wash.) ICF in Phoenix actually worked better at R5 than R25.

The lesson: foam depth has little to do with the dynamic benefit of thermal mass. What counts is the mass' specific heat, or the relative ease with which it absorbs heat during the day and releases it at night. CMU may not be enough mass in Bakersfield, but you can always fill it, and not necessarily with concrete, except that CA code requires concrete IIRC.

As I wrote before, none of this is news to TexasICF, who has blocks to sell and obviously likes some facts better than others.

Say I'm willing to call it even - CMU + 5" exterior foam vs ICF (with 2x2.5" foam but more mass). Was there a conclusion on pricing (say just materials to start)?

ICF: ~$3/sq ft + 6" concrete (perhaps $2/sq ft)
CMU: ~$1.40 sqft + 5" EPS (perhaps $1/sq ft)

Posted By toddm on 27 Mar 2011 09:06 AM
TexasICF:
Exterior foam/interior mass saves more energy than ICF, all things being equal.
Therefore, external foam/interior mass needs LESS foam than ICF to achieve comparable performance.

In a dry climate with wide swings in daily temperature, it could be a lot less foam. In the ORNL study above, interior mass in Bakersfield, CA cut whole building energy use by 18 percent while ICF cut it by not quite 10 percent. If you look at Fig 8, you'll see that ICF's performance in Bakersfield barely changed as ORNL reduced its insulation from R25 to R5 (i.e., that the dynamic benefit of thermal mass increased as R value decreased to the point that energy savings was almost a wash.) ICF in Phoenix actually worked better at R5 than R25.

The lesson: foam depth has little to do with the dynamic benefit of thermal mass. What counts is the mass' specific heat, or the relative ease with which it absorbs heat during the day and releases it at night. CMU may not be enough mass in Bakersfield, but you can always fill it, and not necessarily with concrete, except that CA code requires concrete IIRC.

As I wrote before, none of this is news to TexasICF, who has blocks to sell and obviously likes some facts better than others.

Toddm,  First I must admit I am a big ICF fan for sure -- although I have my favorites -- I am first a fan of ICF in general.   That said, I would prefer someone reading this thread purchase any ICF over my favorites prior to getting confused by all this communication and think that CMU is in the same league -- that is after all, the subject of this thread.

I am an ORNL fan as well and have read this reports numerous times.   These math models graphs ICF performance with R-15 and below - I don't know of any ICFs that have an R-value this low -- I think almost all of them are about 20 or more.   The models also graph Interior and exterior mass scenarios where the R-value of these systems is very high -- something else I haven't seen much out there.     I agree with jonr's point --  if you add 5" of external foam to a CMU wall you will have similar performance of an ICF.   And to your point you will still have less mass and I will add you will also have less strength.

Interestly, the new IECC significantly affects what you can put inside a CMU and have it count toward meeting code.   E.g. foam inserts don't count any more.

I did get a chuckle out of your lesson above -- if "foam depth has little to do with the dynamic benefit of thermal mass" then you wouldn't see any performance difference in the math models for the various systems studied because mass is held constant for each of the various senarios.  Regards.

Obfuscate all you want TexasICF. You can link ORNL research that demonstrates you are full of crap but you can't make people read it. So you win. The dumb customers are yours.

Structurally speaking, the icf will give you a more continuously strong wall. It's one big monolithic slab, where CMU is vertical stems separated by the masonry. Also, the CMU material is not as strong as concrete. And when considering costs, it's very difficult to compare without taking quality and durability into account; and those by nature are hard to quantify.

A shotcrete dome is another animal altogether. If yo want to live inside an eggshell, you can't do it (easily) with CMU or ICF, but yo can't find a corner to put the vacuum cleanerin.

I guess I should have clarified earlier. I would fill my CMU to add mass. Each block as required would have reinforcement and concrete fill. I would drystack, then use a surface bonding agent. So thermal mass is the same as ICF, but no interior insulation. All insulation is added to exterior to meet code. I'm only planning one floor. It still appears to me that the above system is much cheaper, more mass directly exposed, more exterior insulation, and cheaper. Can anyone offer a cost analysis to show me otherwise? Both systems need exterior siding. CMU does not need interior drywall for finished areas. I've seen a lot of opinion in the above replies, but little data. Can anyone offer data, not sales talk?

One can build a CMU or ICF structure to any level of performance - quality, durability, R value or strength . So it comes down to which one does it for the best price.

One way to add strength to a CMU wall is to add horizontal rebar.  This is possible when knock out blocks are used.  Of course, vertical rebar should also be used to anchor the wall to the foundation.

Hey McFish, why would you want to do all that work? Build it with ICF, get it over with and move on. You can always build a more efficient structure, but why kill yourself to save 3 bucks a month? Unless building walls is your hobby...

In general, for a run of CMU wall, horizontal reinforcing won't get you much extra "strength" as it relates to material stresses, until the length of the section of wall in question is less than 2X the height. Then it can start transferring load to the end walls. What it does, however is give it needed continuity and resistance to vertical and stair-step cracks. I've never actually set bond beams, but I understand that it makes the installation of CMU more difficult.