Posted By FBBP on 13 Feb 2012 09:24 PM
My thoughts on mass in Phoenix.

If we say Phoenix temps are 90 during the day and 60 during the evening then the day heat will penetrate the exterior layer of foam, build up in the concrete till some of it penetrates the second layer of foam. With the insulation on both sides, the concrete can hold heat to its specific heat values. How long it takes for the heat to penetrate the two layers is a matter of R value.

If the mass and two layers of foam working as an assembly delay or slow the transfer of the 90º outside temps from reaching the inside for a period of say 6 hours than when the outside air begins to cool, the cost of mechanically cooling the interior will be reduced substantially because the ac unit is now shedding heat to the cooler night time temps rather than the daytime temps. The inside air can now also be cooled by natural ventilation. The heat still residing in the concrete mass will tend to move to the outside again because the outside air is now cooler than the inside air. This amount of heat does not need to be dealt with from the inside. In this case it is also possible that the heat trapped in the concrete mass between two layers of foam might migrate down to the cooler footing as this is the path of least resistance.

With all the insulation placed on the outside, the interior mass can only respond to the heat once it is already in the room. Also once the heat passes the outside insulation, it move readily into the interior space, no interior insulation means that the mass and the room temps will try to equalize. If this were not the case we would have to ascribe a much higher R value to concrete. It would therefore seem that heat gain from other than wall areas (windows etc.) will soak into the bare mass for a period of time in the morning but once the outside heat passes the outside insulation, this will stop and it will be the outside heat that is soaking the mass and than the mass will radiate it into the room. (heat transfer direction changes as the mass approached higher outside temps.) In the evening/nighttime, all the heat has to be dealt with as the heat will not go back through the foam to the cooler outside temps. ‘course you will still have the benefit of the cooler outside temps to work with.
So if most of the heat is coming from the walls ICF has the advantage. If most is coming through windows etc. external insulation has an advantage till the mass is effected by the outside temps, then because it becomes a radiator it becomes a disadvantage.
Feel free to disagree but please give logical explanations so that your reply builds up the knowledge base on this forum.

Posted By jmagill on 14 Feb 2012 06:35 AM

What you think and what the facts are are two different things. Having all the insulation on the outside doubles the time it will take for the heat to move to the interior wall.Having no insulation on the interior wall allows the concrete to react faster to the heat in the room, the whole point of having no insulation hindering the flow. Exactly what you want. Insulation on the outside to slow the heat coming in through the walls. Concrete on the inside so it can quickly react by absorbing the interior heat. The studies have already proven it. You have not. You have not given logical explanations or built up any knowledge base. It is all supposition.

jmagill - What you say is no different than what I said except that you seem to imply that NO heat will come through the wall. If you have sufficient insulation on the exterior you can slow it down. If you don't, than the mass becomes the enemy. Its just like a radiant floor at full temp.

Posted By jmagill on 14 Feb 2012 06:35 AM


What you think and what the facts are are two different things. Having all the insulation on the outside doubles the time it will take for the heat to move to the interior wall.Having no insulation on the interior wall allows the concrete to react faster to the heat in the room, the whole point of having no insulation hindering the flow. Exactly what you want. Insulation on the outside to slow the heat coming in through the walls. Concrete on the inside so it can quickly react by absorbing the interior heat. The studies have already proven it. You have not. You have not given logical explanations or built up any knowledge base. It is all supposition.

Posted By Lbear on 14 Feb 2012 12:45 PM

Posted By jmagill on 14 Feb 2012 06:35 AM


What you think and what the facts are are two different things. Having all the insulation on the outside doubles the time it will take for the heat to move to the interior wall.Having no insulation on the interior wall allows the concrete to react faster to the heat in the room, the whole point of having no insulation hindering the flow. Exactly what you want. Insulation on the outside to slow the heat coming in through the walls. Concrete on the inside so it can quickly react by absorbing the interior heat. The studies have already proven it. You have not. You have not given logical explanations or built up any knowledge base. It is all supposition.

While having the entire mass on the inside with no insulation is the ideal scenario, as shown by the studies, it still does not mean that ICF is completely useless in the thermal mass department. The concrete in ICF does contribute to thermal mass, just not as ideally as a SCIP would.

Where does that live one with? SCIPs, which are even harder to find a qualified SCIP contractor and the costs of SCIP are even more than an ICF home. Also, many people like a drywall finished interior, so having a concrete wall on the interior will turn off many people. Each system has its pros and cons but ICF claiming that the thermal mass in ICF is of no consequence is not accurate either.

Posted By jmagill on 14 Feb 2012 12:56 PM


I completely agree. Mass in an ICF wall has benefit. It however is less benefit than having the mass completely with in the insulation. We just happen to have a few ICF contractors who can not live with that benefit and have to try to claim more. It is kind of like the whole claim of 5 inches of foam and 6 inches of concrete equaling 50 rvalue.

Posted By BrucePolycrete on 15 Feb 2012 08:05 PM
We will stipulate that 5 inches of EPS is R22 - 23. Any ICF manufacturer claiming their 5" thick EPS product is anything else is being deceptive. I would be surprised to learn that any of them continue to do so. This is not debatable, it's fact.

ICF has many other benefits that make it a superior choice over a flimsy stick built wall. Avoid stick built walls, they attract tornadoes, hurricanes and fire.

Posted By toddm on 15 Feb 2012 07:50 PM
That's some study you found, Lbear: basically it is ICF-is-better-than-crap-production-houses I with a double deception baked in.

An R50 cavity stud wall would require -- what? -- 2x16s? One suspects that 5 minutes into a real world exercise, the designers would be adding foam board sheathing to the exterior or drawing up a double stud wall, either of which would dramatically improve whole wall figures. This is the fundamental deception in the ICF industry's ongoing better-than-crap campaign. Yes, whole wall numbers are the important ones. No, you don't have to pour concrete to improve them.

But real howler here is the mass effect adjustment. CTL used a code compliance program for commercial buildings to account for ICF's mass in the 38 cities. The engineering firm disclaimed it thusly: such use "may not be applicable to residential buildings; however, in our opinion, it is adequate for comparison purposes." Alas, it is not adequate as a base for insulation claims, so you will find ICF literature saying "performance up to R50" while it rates the blocks at R20ish.

One would hope that the average attentive consumer would ask why, if R50 is legit, the company says R21. The above average attentive consumer might also ask why the CTL study didn't use the Department of Energy's modeling software, developed at Oak Ridge National Laboratory for the specific purpose of quantifying mass-enhanced R values.

Could it be that the result would fall far short of R50, and embarassingly so?

Posted By toddm on 16 Feb 2012 12:26 PM
I am not inclined to guess about what's reasonable for ICF's mass effect in Phoenix, and I certainly won't accept anything the industry says about it short of proper testing.
If form companies could claim mass-enhanced values in the 30s, you'd expect them to do so, no? Here is hybrid ICF manufacturer Rastra doing just that: http://www.rastra.com/ThermalPerformance.html

Posted By toddm on 16 Feb 2012 05:00 PM
I guess I am missing your point about fiberglass. Testing doesn't catch its flaw so all testing is bad? That's silly. Or ORNL's mass effect testing specifically is bad? Possibly. Let's see some research indicating so. Otherwise, that the ICF industry ignores an accepted test while tossing around anecdotes and sketchy science is a completely different kettle of fish. If a seller won't provide me information by accepted standards, how is it my duty to guess?

But just to make you happy, yes, ICF will have a mass effect in Phoenix. I showed you an ORNL chart that suggests that R17 ICF would be a mass-enhanced R28ish. But R22 is still a jump ball. I also showed you an ORNL chart showing a decline in annual energy savings as ICF R value increased. It makes sense that more foam would push the wall's response time beyond the diurnal cycle that generates savings. But that's conjecture and we've had enough of it on this thread to last us a lifetime. If I were committed to ICF, as you appear to be, I would be quite upset that form makers are withholding information I need to make good decisions.

Posted By Lbear on 17 Feb 2012 04:09 AM

Posted By toddm on 16 Feb 2012 05:00 PM
I guess I am missing your point about fiberglass. Testing doesn't catch its flaw so all testing is bad? That's silly. Or ORNL's mass effect testing specifically is bad? Possibly. Let's see some research indicating so. Otherwise, that the ICF industry ignores an accepted test while tossing around anecdotes and sketchy science is a completely different kettle of fish. If a seller won't provide me information by accepted standards, how is it my duty to guess?

But just to make you happy, yes, ICF will have a mass effect in Phoenix. I showed you an ORNL chart that suggests that R17 ICF would be a mass-enhanced R28ish. But R22 is still a jump ball. I also showed you an ORNL chart showing a decline in annual energy savings as ICF R value increased. It makes sense that more foam would push the wall's response time beyond the diurnal cycle that generates savings. But that's conjecture and we've had enough of it on this thread to last us a lifetime. If I were committed to ICF, as you appear to be, I would be quite upset that form makers are withholding information I need to make good decisions.

The point about fiberglass is that it is still toted today that R-13 batts are actually R-13, when we know they are NOT. Yet nothing is done about this and many people still buy the R-13 misinformation and manufacturers can still sell R-13 at Lowes and Home Dept and nobody calls them on it.

EVERY building method has sketchy data at times. While the lumber industry is the predominant building technique in the USA, it is far from being truthful and honest in its claims. Without getting into all of their questionable claims, we can spend all day on how the lumber of today is of lesser and lesser quality due to the young growth trees they are using. Get a "straight" 2x4 at Lowes, leave it a garage for a month and you no longer have a "straight" 2x4.

Even SCIP has its problems and questionable data. Again, not to go off topic but SCIP builders claim the cost to do SCIP is equal or less than a wood framed home. When I got quoted for SCIP it was off the charts expensive. There is no way it equals or is less than a wood framed home cost to build.

The point is that ALL manufacturers make questionable claims and they ALL like to trash the opposing methods. It's like the Ford vs Chevy debates. Each claims their vehicle is better and each one has reports and studies claiming theirs is better. It never ends.


I ask again, what are my options? Wood or ICF? Which would you choose? You know you would pick ICF.