Posted By lzerarc on 16 Feb 2011 08:53 AM

Posted By dmaceld on 15 Feb 2011 11:41 PM

Posted By lzerarc on 15 Feb 2011 10:30 PM
..this does not make any sense...what I am doing wrong? .....

For the foam-concrete-foam configuration the heat flow path is in series, through one, then the next, and so on. In this case you add the R values together. In a stud wall when you're looking at the studs and in-between space it's a parallel path. In that case you take the u values and multiply them by the % area, like you are trying to do w/ the concrete and foam. Add them together for a total u, then convert that to R value and add the R values of the interior drywall and exterior finish.

If you want to take it to the extreme do that for the wall space, then the window area, and the door area, convert each to u value, multiply by the area %, add together, then convert back to R.

So, in short, for parallel use u, for series use R. HTH

ok, thats easy enough to understand. However if it is just a simple r value addition....isnt that what ICF builders are saying how NOT to compare it?  How does that take into account the mass?
That article (u value vindicated) is interesting, but (at least I can not find it) however it shows the u of ICF is so much better.  They simply just state it is a lot better.  Unless you are implying the r-21 of the block is a u of .048....in which case, once again, is just a simple r value comparison.  I know I have to be totally missing something here.......

Here is the direct link to the R-U Value Vindicated article:

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

To answer your question about thermal mass; it doesn't really even come into play when comparing steady state total wall R or U values verses the R or U values of the individual components.  It is all about whether the R values of the individual components are in parallel or series.

If you had any schooling in electrical circuits, this is analogous to electrical resistors connected in series vs. parallel.  Series resistors are additive.  Given Rt = total circuit resistance and R1 = Resistor #1 and R2 = Resistor #2, for a series circuit, Rt=R1+R2.  Simple enough.  The total circuit resistance is the sum of the two individual resistors.  Assume R1 = 10 ohms and R2 = 10 ohms.  Then Rt series = 20 ohms.  But for two resistors in parallel, this doesn't work.  As you might imagine, electrical current will flow easier when two resistors are in parallel rather than in series.  In fact, assuming two resistors of equal size, the total parallel resistance will be less than the resistance of any individual resistor.  To calculate the total circuit resistance in a parallel circuit, we have to take the inverse of R or 1/R.  In our parallel example here lets assume we have two 10 ohm resistors in parallel.  In this case we calculate parallel resistance by 1/Rt = 1/R1 + 1/R2 or 1/Rt = 1/10 + 1/10 or 2/10.  Since 1/Rt = 2/10, the inverse of each results in Rt parallel = 5 ohms.  See the analogy with wall insulation R and U values?

With a typical wood stud wall construction with insulation in the cavities between the studs, the studs are in parallel with the cavity insulation.  Ignoring the interior drywall and exterior sheathing for now, heat flowing from one side of the wall sees stud-insulation-stud-insulation-stud-insulation and so forth all in the same plane.  The low R value studs provide essentially a thermal short circuit for the heat flow compared to the insulation in the cavities between the studs (and the wood bottom plate and wood double top plate, and window and door wood headers, etc).  This is the parallel resistance issue where you have low R value products in parallel with high R value products.  The heat, like electrical current or water flow, follows the path of least resistance.  This is why a 2x4 stud wall with perfectly installed R13 fiberglass batts has a total wall R value of ~R10 if tightly constructed (even less if not tightly constructed) even though the studs comprise only a small portion of the wall.  Even if you fill the cavities with premium spray foam at ~R23, the total wall R value only increases to ~R13 because of the low parallel thermal resistance offered by the wood studs.

Now with an ICF wall (and SIPS to a lesser degree considering the wood splines between panels), there are essentially no parallel thermal short circuits.  Everything is effectively in series.  There are no studs or thermal short circuits in parallel with the insulating foam - just a solid plane of foam.  And when calculating steady state R value, you can essentially ignore the concrete since its R value is so low.  Given R10 foam on the inside, R0 concrete, then R10 foam on the outside, you get the total series R value of R20. 

Now interior drywall and exterior sheathing would likely add some R value here because both of these are in series with the wall.  But it would apply essentially the same to either a stud wall or ICF wall or SIP wall.

All of the above is ignoring the dynamic effects that occur when exterior temperatures fluctuate up and down in high mass walls like ICF, i.e. the mass effect.  That is explained in one of the previous links.

Posted By lzerarc on 16 Feb 2011 08:53 AM

ok, thats easy enough to understand. However if it is just a simple r value addition....isnt that what ICF builders are saying how NOT to compare it?  How does that take into account the mass?

Go back and look at my long post on page 7 of this thread. It's dated 06 Feb 2011 09:12 PM.

Making a direct comparison of a typical frame wall and ICF is dicey, unless you are talking in terms of long term steady state situation. The thermal mass of the concrete retards the net flow of heat back and forth through the wall. A fiberglass or cellulose insulated wall does not store heat like the ICF wall.

Two illustrations. Think of a house built with walls made of 100 foot thick stone. Intuitively you can see how it would take many weeks, or months for heat to travel from one side to the other. In fact the stone will store so much heat, and thus retard its flow, that the 100°F summer temp of a dessert might not be felt on the inside until fall, and the winter temp will finally reach the inside in the spring. Thus you could end up with the situation of heating the interior in the summer and cooling it during the winter! I know this is a ridiculous scenario, but I think you can see the point. How much cellulose insulation would it take to accomplish the same thing? Who knows if it's even possible, but you would have to have an R value of what, 1000 or more? The R value of 100' of stone would be what, 100?

Second illustration. Two different water tanks, one 10 gal and the other 100 gallons. Each has a 1" inlet near the bottom and a 1" outlet near the top. Now start pumping water into each tank at the rate of 2 gpm. In 5 minutes water will start leaving the 10 gal tank, but it will be 50 minutes before it leaves the 100 gal tank. Now consider what happens if we stop pumping in after only after 30 minutes and start draining back. You can easily see that 50 gal of water will have passed all the way through the 10 gal tank, but the 100 gal tank is still not full and no water passes through the outlet. In this case both tanks have an equal resistance to water flow, but the 100 gal has an effective resistance much greater than the 10 gal. Saying the 100 gal has an effective resistance of 2x, 5x, or 10x more than the 10 gal is perilous, but we know it does a better job of keeping water from flowing through from the inlet to the outlet, as long as the water flow into the tank cycles in and out. I'll let you imagine the comparison if the 100 gal tank has 1/2" inlet and outlets and the 10 gal 1".

Do these simplistic illustrations help?

ok, thanks all. I do understand how the mass works, that is not really the issue. I also understand the short circuiting of studs, that was never really a question. Most compare ICF to the code basic 2x4 framing (or 2x whatever, the point still applies) but my proposed framed system is a lot better then the basic as well. My real question is ICF/mass performance in "non ideal" locations....cold climates. Everything I read says it buffers, hot days and cold nights....concrete minimizes interior temp swings as long as the high and lows are above and below interior settings. However with prolong periods of cold weather well under the interior temp, the mass cools down, and stays cold for 4-6 months, never being allowed to warm above 70 or whatever its set at. The EPS is then acting like a foam cooler around an ice cube IMO. This is my question that I am not understanding...doesn't cold climates make the mass affect next to useless, or perhaps even worse vs a high r, thermally broken wall assembly (an assembly that next to eliminates any stud "short circuiting")?

Arkie, I know you love the stuff, but you're understating the clear-wall R of an R13 batt-insulated 2x4 wall by a significant amount (your thumb is a bit too obvious on the scale?).

R10-R11 may be close for "typical" installation practices, but for tight and well-installed a wood sided wood-sheathed 16" o.c. 2x4 wall with R13 fiberglass yields about R12.5. Bump the framing to 24" o.c. and an R13 wood clad studwall rises to ~ R13.5, which is a HELUVA performance difference from "...closer to R9 or 10..."

I'll trust the folks who actually MEASURE the stuff in a climate simulation chamber: http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/Calc.htm

To be sure, exterior foam over a studwall can be a cheap & effective performance enhancement by putting a significant thermal break over those framing shorts.

R value may not be R value when comparing center cavity studwall R with other wall assemblies with fewer thermal shorts , but "clear wall R" value pretty much is "clear wall R", and the folks at Oak Ridge really do know their stuff.

"Whole wall" R is an estimate based on typical glazed area as a fraction of the entire wall, but difference in fractional glazed area (and glazing U-value) has a much bigger effect on actual whole-wall-R than whether the wall assembly is stud & fiber vs. ICF vs. SIP. The dynamic advantages to ICF are primarily in climates with high diurnal temperature swings. At R25+ the effect of the thermal mass is measurable in a lab, but in real world designs other factors can easily swamp the mass-advantage.

Moving the bulk of the R to the exterior in an ICF allows the thermal mass to participate more, but the effect is still relatively modest in heating dominated climates. In modest- R15-R20 ICFs with typical "other" design factors it reaps only single-digit percentage heating-energy savings. Even with half or all of the concrete on the interior, such exterior foam only, or center-insulated concrete this is true. With the more typical insulation/concrete/insulation stackup of an ICF you get low-mid single-digit percentage savings over stick built: http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/figures/figure6.pdf From a whole-house design point of view there are numerous ways to get similar or better improvements in primary energy above standard stick-built performance for less cash up front (adding an inch exterior foam sheathing to the studwall being but one approach.) It's easy to overstate the value of that thermal mass to the point of absurdity- those dynamic effects SHOULD be ignored, unless you're modeling the entire house (at which point the low-relevance in most applications becomes even clearer).

Air-sealing ICF (and SIPS) is easier than with other wall assemblies, but air-tightness is by no means guaranteed, with myriad real-world counterexamples.

Yes, ICFs are a great (and durable) way to build, but selling it primarily on a comparative energy efficiency investment basis is a losing proposition. An inch of foam on a 2x6" 24" o.c. spray-cellulose filled studwall will outperform an R20 ICF by about 15-20% in most climates.

"Yes, ICFs are a great (and durable) way to build, but selling it primarily on a comparative energy efficiency investment basis is a losing proposition. An inch of foam on a 2x6" 24" o.c. spray-cellulose filled studwall will outperform an R20 ICF by about 15-20% in most climates."

I agree with you that selling ICF based only on energy investment may be a stretch.   Nevertheless, apart from the fact that it wins in virturally every other category --- Here are my calculations (ignoring thermal mass, air infiltration and the passage of time which are each in favor of the ICF).

ORNL says framing factors are really closer to 25% due to floors, headers, fire horizontals, etc. but I'll use %20.   I'm using R1 per inch for the wood and R4 per inch for the spray cellulose.  I'm using R-6 per inch for the continuous one inch foam that is mechantically attached.


Actual R    = R Continuous 1in foam + R 2x6 wall     

2x6 wall has different rvalues in parallel to heat flow (wood and cellulose).

Actual R    = 6 + 1/((.25/(1*5.5)+.75/(4*4.5)) 
   
                  = 6 + 1/((.25/5.5)+(.75/18))

                  =  6 + 1/(0.045455 + 0.041667)

                  = 6 + 1/0.087122 

                  = 6 + 11.48 =  17.48

Your typical ICF has an R-value of 22.   Applying the same equations utilizing a 2x8 or thicker external would probably do it. Regards.

Posted By Dana1 on 16 Feb 2011 11:54 AM
Yes, ICFs are a great (and durable) way to build, but selling it primarily on a comparative energy efficiency investment basis is a losing proposition. An inch of foam on a 2x6" 24" o.c. spray-cellulose filled studwall will outperform an R20 ICF by about 15-20% in most climates.

My brother was involved in the manufactured housing business for several years. Obviously, ICF walls are not an option for manufactured housing. They are mostly 2 x 6 frame tightly sealed and thoroughly insulated. My brother commented once that the one thing MH owners never complained about was their heating bills.

Polycrete makes panelized walls that include door/window bucks and rebar. They're delivered to your jobsite to be dropped in place with a sign crane.Very Cool. Here's a link with some pictures.
http://www.polycrete.com/en/prefab

Posted By TexasICF on 16 Feb 2011 03:10 PM

"Yes, ICFs are a great (and durable) way to build, but selling it primarily on a comparative energy efficiency investment basis is a losing proposition. An inch of foam on a 2x6" 24" o.c. spray-cellulose filled studwall will outperform an R20 ICF by about 15-20% in most climates."

I agree with you that selling ICF based only on energy investment may be a stretch.   Nevertheless, apart from the fact that it wins in virturally every other category --- Here are my calculations (ignoring thermal mass, air infiltration and the passage of time which are each in favor of the ICF).

ORNL says framing factors are really closer to 25% due to floors, headers, fire horizontals, etc. but I'll use %20.   I'm using R1 per inch for the wood and R4 per inch for the spray cellulose.  I'm using R-6 per inch for the continuous one inch foam that is mechantically attached.


Actual R    = R Continuous 1in foam + R 2x6 wall     

2x6 wall has different rvalues in parallel to heat flow (wood and cellulose).

Actual R    = 6 + 1/((.25/(1*5.5)+.75/(4*4.5)) 
   
                  = 6 + 1/((.25/5.5)+(.75/18))

                  =  6 + 1/(0.045455 + 0.041667)

                  = 6 + 1/0.087122 

                  = 6 + 11.48 =  17.48

Your typical ICF has an R-value of 22.   Applying the same equations utilizing a 2x8 or thicker external would probably do it. Regards.

Again, lowballing the actual whole-wall R value of the stick built assembly generates a mis-compare.  (The R4 K value for cellulose was unrealistically generous, but the rest is skewed in other directions.)

The ORNL calculator numbers are derived from real data taken on real test assemblies in a climate simulation chamber, and not based on a simple-arithmetic model.  According to the calculator the clear wall R of a cellulose insulated  2x6 24" o.c. wall  with R4 of foam and wood siding tests at a bit over R24.  Their whole-wall R calc (all thermal shorts included) comes out at a bit over R18.5.   I tend to believe people who actually measure stuff, measure it repeatedly for verification, and don't have a financial interest in the result.  It's not a stretch to estimate that turning that inch of EPS in the ORNL calculator into an inch of iso or closed cell SPF (as you did in the simple-arithmetic model) would test at ~R20.5-R21.

Using a software-only but more sophisticated simulation used by the folks a Building Science it would be over R19 using an inch of EPS, around R21 with iso.  (See assembly 2a, make adjustment for XPS vs. EPS vs. iso, and cellulose vs. fiberglass, but with iso you'd be ~R21 in that sim.  Then compare it with 7b.)

And of course, you've included ZERO thermal shorts for the ICF (not around doors & windows, not where floors intersect walls, nor any earth-coupled heat loss to the footing in heating dominated climates) which is not even close to reality. But then you didn't add any for siding either, so if you subtract R1  for the thermal-short reality and add R1 for some siding, you're still hitting around  R20 whole wall (best case) for an R20 ICF.
So mayhaps it's a stretch say it outperforms an R20 ICF by 15%, when they're actually pretty equivalent, eh?   (The 3-5% higher R for the stick built assembly is offset by 3-5% thermal mass factor of the concrete in heating dominated climates, again according to ORNL modeling based on better data and math than we're going to put into a forum post.)

Oh, you said most ICF are now R22?  

Add 1/4 inch to the iso- make it 1/2", just for good measure, to balance the positive & negative temperature coefficients between iso/EPS.  It's not that expensive to make it somewhat thicker stock. 

Heck, go hog wild add 3" of iso and get ~R35ish whole wall numbers out of it (while eliminating all condensation/mold issues related to stick build for 99% of the lower 48 of the US).  It's still an easy assembly to build, and build well, at a better price/performance (thermal) than concrete construction, and at a high enough R that real savings can be made on mechanical systems to offset the cost of the foam.  If it's about going for high thermal performance, price/performance has to count. (I haven't seen any PassiveHouse designs that went with ICF, but maybe there are some.  Not all PassiveHouse builders/buyers are super cost-sensitive.)

The point is, people can and DO stick-build to a far better standard than compressed & ill-cut batts in 2x4 construction that it would take to reduce R13 batt construction to an R9 whole wall R.  And it's not very expensive to get very decent thermal performance with a nominal pass at air sealing and a modest amount of exterior foam, and whole-wall numbers improve significantly when advanced framing techniques are used (typically at a cost savings up front.)  Comparing ICF to a 2x4 house with batts barely eking R9 average out of R13 batts is comparing to a standard that doesn't even meet code and wouldn't pass inspection in many areas (not that there aren't plenty of examples of such construction).  Claiming that ICF performs better than a piece of crap  doesn't make make the case, it only evokes a credibility issue when such comparisons are drawn.  (What, it's only better then a piece of crap?)

Don't oversell ICF on thermal performance, since it's a loser from an R/$ point of view. (R-value IS R-value when looking at clear wall/whole wall numbers).  But it's a clear winner on several other fronts. Contrary to what you might presume from the tone of this and my prior post I'm all for it.  I'm just against selling the thermal performance aspects by misrepresentation & straw man arguments regarding other construction methods.  ICF has enough going for it without going there.

Posted By Dana1 on 16 Feb 2011 11:54 AM
Arkie, I know you love the stuff, but you're understating the clear-wall R of an R13 batt-insulated 2x4 wall by a significant amount (your thumb is a bit too obvious on the scale?).

R10-R11 may be close for "typical" installation practices, but for tight and well-installed a wood sided wood-sheathed 16" o.c. 2x4 wall with R13 fiberglass yields about R12.5. Bump the framing to 24" o.c. and an R13 wood clad studwall rises to ~ R13.5, which is a HELUVA performance difference from "...closer to R9 or 10..."

I'll trust the folks who actually MEASURE the stuff in a climate simulation chamber: http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/Calc.htm

Dana, I wasn't attempting to calculate clear wall or whole wall R value (interior and exterior sheathing, air films, etc).  As I stated, I was ignoring the interior drywall and exterior sheathing for my calculation since those factors are in series and would be additive to either a stud wall or ICF wall.

I arrived at my value of ~R10 for the 8' tall 2x4 stud wall @ 16" oc with R13 batt insulation (just the studs, top and bottom plates, and cavity insulation) as follows:

Each typical 8' high x 16" 2x4 stud wall section contains (1) 92.5" stud plus (2) 16" top plates plus (1) 16" bottom plate for a total 2x4 length of 140.5".  Multiply this by the 2x4 width of 1.5" and you get 210.75 in sq.  The total wall section area is 97"x16" = 1552 in sq.  The 2x4 portion of that section of wall then comprises 210.75/1552 x 100% = 13.6%.  I rounded this to 14% then conservatively added 6% more for additional wood typically included in window and door headers, sides, and sills, and corners and partition intersections.  Thus, I'm using 20% of wall area is wood, and the remaining 80% is insulation.  The ORNL link above shows that window and door headers, sides, and sills alone comprise more than 6% of a typical wall section, so my estimation that 20% of wall area is wood is conservative.

I used a generous R1.4 per inch for the 2x4s giving ~R5 for a 3.5" thick member.

Wall U = (0.20 x 1/Rwood) + (0.80 x 1/Rinsulation)
Wall U = (0.20 x 1/5) + (0.80 x 1/13)
Wall U = (0.20 x 0.20) + (0.80 x 0.077)
Wall U = (0.04) + (0.062)
Wall U = 0.102

Wall R = 1/Wall U
Wall R = 1/0.102
Wall R = 9.8

Now if you take the R9.8 I calculated above just for the 2x4s and R13 insulation and add 1/2" interior drywall (R0.45), interior air film (R0.68), 1/2" exterior sheathing (R0.63), wood siding (R0.80), and exterior air film (R0.17) you get the following complete wall assembly R value:

9.8 + 0.45 + 0.68 + 0.63 + 0.80 + 0.17 = 12.53.

Here is where I got the R values for the wall components listed above:

http://www.coloradoenergy.org/proco...values.htm

TexasICF-

Concerning your calculations of heat loss through a wood stud wall, I have some comments.  You say that you will use a framing factor of 20% in your calculations, but your example uses 25% instead.  Your thickness for the cellulose inexplicably uses 4.5" instead of 5.5".  Correcting these two items would give R for the wall without foam of 13.75.  Studs use softwood, and typical R-values are:
R=1.41  http://www.energysavers.gov/your_ho...opic=10170
R=1.41  http://en.wikipedia.org/wiki/R-value_(insulation)
R=1.25  http://www.sizes.com/units/rvalue.htm
Averaging these together gives R_softwood = 1.36.  This gives a clear wall R-value of 14.05.  Around here they put OSB sheathing on before the foam, which has a R-value of 0.5, so total wall without exterior foam is 14.55.  Adding 1" of XPS adds about 5.3 (http://www.xpsa.com/enviro/longterm.html) for a total of about 19.9.  

These results depend strongly on the framing factor.  The California Energy Commission did a study and came up with a framing factor of 27% for California compared to 25% for the rest of the US.    http://www.energy.ca.gov/title24/20...ACTORS.PDF   
However their numbers include the rim joist area, which dramatically increases the framing factor since the floor joists are more closely spaced than the wall studs.  (See footnote on table in their Executive Summary.)  For my house the rim joist surrounds a conditioned crawl space, and I do heat loss calculations for it separately from the wall, since it is more highly insulated than the walls (6" fiberglass, 1.5" to 2" sprayed foam, and 2" XPS on outside for the rim joists).  

The California study and U.S. overall study were for studs on 16" o.c., because they found few homes with studs 24" o.c.  The California study includes the following comment concerning stud spacing effect on R-values, "Table 2.3 lists the values given in the Canadian Model National Energy Code for Houses. These sources represent a large variation in the amount of framing: from 15% to 25% for 16” stud spacing and from 9% to 22% for 24” stud spacing."  Therefore, your assumption of a framing factor of 25% for 24" o.c. walls is not well supported.  A value of about 20%, or 22% on the top end, seems more reasonable, maybe lower if the rim joists are excluded and handled separately. 

Lee Dodge
http://www.residentialenergylaboratory.com
in a net-zero energy house

arkie56-

I think anybody trying to build an energy efficient house would not consider 2x4 construction in this era.

Lee

Posted By lzerarc on 16 Feb 2011 11:34 AM
ok, thanks all. I do understand how the mass works, that is not really the issue. I also understand the short circuiting of studs, that was never really a question. Most compare ICF to the code basic 2x4 framing (or 2x whatever, the point still applies) but my proposed framed system is a lot better then the basic as well. My real question is ICF/mass performance in "non ideal" locations....cold climates. Everything I read says it buffers, hot days and cold nights....concrete minimizes interior temp swings as long as the high and lows are above and below interior settings. However with prolong periods of cold weather well under the interior temp, the mass cools down, and stays cold for 4-6 months, never being allowed to warm above 70 or whatever its set at. The EPS is then acting like a foam cooler around an ice cube IMO. This is my question that I am not understanding...doesn't cold climates make the mass affect next to useless, or perhaps even worse vs a high r, thermally broken wall assembly (an assembly that next to eliminates any stud "short circuiting")?

I would say that the thermal mass provided by an ICF provides very little if any energy benefit when outside temperatures remain very cold for long periods of time.  But I would assume that your local climate eventually reaches a point during the year where outside temperatures swing above and below your indoor setpoint?  During these time periods the mass of the ICF wall would buffer out the highs and lows and you may not require any supplemental heating or cooling during those times.  But this would be a relatively minor benefit in a northern climate in my opinion.

Cooling dominated climates definitely see the most benefit from the mass in an ICF wall.  But what is odd is that almost every major manufacturer of ICFs in North America is either in Canada or in the northern US.  This adds to the shipping costs for us down south using ICFs.

Note that I am building my own home using ICF, but I don't do this for a living (thankfully because I'm so slow I would never make any money at it) - being an electrical engineer at a electrical power plant is what pays the bills for me.  Also note that my primary reason for choosing ICF was not thermal performance, but strength.  I like the safety factor that an ICF home provides when the weather becomes violent and we have our share of tornadoes down here. 

This tornado passed within a mile of my property near Atkins, AR in 2008:

http://www.nytimes.com/2008/02/07/us/07tornado.html

We've had several smaller ones within a 5 mile radius since then.

You should see the amount of rebar I currently have in my walk-out basement walls (more to come when I get to the main floor walls). 

The thermal performance was a consideration for sure when deciding on what to build, with ICF being better than or equal to anything typically constructed down here.  Another consideration was the poor quality of building lumber today.  When just building the bracing for my ICF walls, I probably had to cull 1/3 of the 2x4s because they were too crooked or twisted.  And these were considered "premium" quality studs.

Posted By Lee Dodge on 16 Feb 2011 07:29 PM
arkie56-

I think anybody trying to build an energy efficient house would not consider 2x4 construction in this era.

Lee

Even if you go with wood frame 2x6 @ 24" on center with R19 fiberglass batts and 1/2" foam exterior sheathing with 7/16" OSB in the corners for shear with brick veneer (this is typical energy efficient home construction here), you are looking at less than R14 Whole Wall R-Value using the ORNL link that Dana provided here:

http://www.ornl.gov/sci/roofs+walls...S/Calc.htm

Okay Dana1 -- you are making my head hurt.  Nevertheless, I do appreciate it.   :)

Again, lowballing the actual whole-wall R value of the stick built assembly generates a mis-compare.  (The R4 K value for cellulose was unrealistically generous, but the rest is skewed in other directions.)

True, I was generous with the cellulose but the only other matter is perhaps wood is really R-1.1 to R-1.3 or so instead of 1.0.


The ORNL calculator numbers are derived from real data taken on real test assemblies in a climate simulation chamber, and not based on a simple-arithmetic model.  According to the calculator the clear wall R of a cellulose insulated  2x6 24" o.c. wall  with R4 of foam and wood siding tests at a bit over R24.  Their whole-wall R calc (all thermal shorts included) comes out at a bit over R18.5.   I tend to believe people who actually measure stuff, measure it repeatedly for verification, and don't have a financial interest in the result.  It's not a stretch to estimate that turning that inch of EPS in the ORNL calculator into an inch of iso or closed cell SPF (as you did in the simple-arithmetic model) would test at ~R20.5-R21.

Are we not talking about similar numbers if I was at 17 plus with my model and they are at 18 plus with siding?  BTW they ORNL calculator does not include ICF as an an option.

Using a software-only but more sophisticated simulation used by the folks a Building Science it would be over R19 using an inch of EPS, around R21 with iso.  (See assembly 2a, make adjustment for XPS vs. EPS vs. iso, and cellulose vs. fiberglass, but with iso you'd be ~R21 in that sim.  Then compare it with 7b.)

It's your typical builder and architect that have claimed whatever the cavity is as their r-value.   Even with these more sophisticated models you are still below the typical ICF value of approximately r22.

And of course, you've included ZERO thermal shorts for the ICF (not around doors & windows, not where floors intersect walls, nor any earth-coupled heat loss to the footing in heating dominated climates) which is not even close to reality. But then you didn't add any for siding either, so if you subtract R1  for the thermal-short reality and add R1 for some siding, you're still hitting around  R20 whole wall (best case) for an R20 ICF.

Do you have to say "of course"?   Actually, if you go with ripped 2x8 (for a 6" concrete all) and put the frame entirely on the inside of the foam.   This common approach replaces the concrete R-value with wood which is comparatively much higher.  Thus R-26 or so around the windows and doors.   The floor to wall intersection does provide (depending on how one does it) a very small bridge perhaps r-1 as you said.  I'm with you on the heating dominated climates -- in fact my next house i build will carry the walls down a foot or two underground to uncouple porch, driveway etc. etc.   Don't forget, however, that this earth coupling also helps quite a bit depending on the time of year.
So mayhaps it's a stretch say it outperforms an R20 ICF by 15%, when they're actually pretty equivalent, eh?   (The 3-5% higher R for the stick built assembly is offset by 3-5% thermal mass factor of the concrete in heating dominated climates, again according to ORNL modeling based on better data and math than we're going to put into a forum post.)

I must agree with you that it is a stretch.   Also, having read just about all that I can from ORNL on this subject, even in Minn. the thermal mass effect is about 8% better than conventional and this is only if the assembly is built to the same r-value.   Also, as you know, r-value does not address or include thermal effects at all.

Oh, you said most ICF are now R22?  

I can't speak for all of them but most of the major brands are about R22.   The one I prefer is R22.4.

Add 1/4 inch to the iso- make it 1/2", just for good measure, to balance the positive & negative temperature coefficients between iso/EPS.  It's not that expensive to make it somewhat thicker stock. 

I'm not sure what your saying here exactly but you can add thickness to the ICF too.  E.g. with panels of differenct thicknesses.   etc.

Heck, go hog wild add 3" of iso and get ~R35ish whole wall numbers out of it (while eliminating all condensation/mold issues related to stick build for 99% of the lower 48 of the US).  It's still an easy assembly to build, and build well, at a better price/performance (thermal) than concrete construction, and at a high enough R that real savings can be made on mechanical systems to offset the cost of the foam.  If it's about going for high thermal performance, price/performance has to count. (I haven't seen any PassiveHouse designs that went with ICF, but maybe there are some.  Not all PassiveHouse builders/buyers are super cost-sensitive.)

I can't really disagree with this except to add that my grandchildren will be watching these guys rebuild in 50 to 75 years and sooner if one uses 24 inch O.C. studs.  Even if i didn't like ICF I would still build to last and not build to fall down. 

The point is, people can and DO stick-build to a far better standard than compressed & ill-cut batts in 2x4 construction that it would take to reduce R13 batt construction to an R9 whole wall R.  And it's not very expensive to get very decent thermal performance with a nominal pass at air sealing and a modest amount of exterior foam, and whole-wall numbers improve significantly when advanced framing techniques are used (typically at a cost savings up front.)  Comparing ICF to a 2x4 house with batts barely eking R9 average out of R13 batts is comparing to a standard that doesn't even meet code and wouldn't pass inspection in many areas (not that there aren't plenty of examples of such construction).  Claiming that ICF performs better than a piece of crap  doesn't make make the case, it only evokes a credibility issue when such comparisons are drawn.  (What, it's only better then a piece of crap?)

Yes, a some percentage do build better but standards are pretty low.  If one ill-cuts batts in 2x4 construction they will actually get something more like an R5 or less for these areas.  These calcs are assuming not air infiltration.  

ICF schools are being built now that utilize kBTU that are 1/3 of the coveted Energy Star Rating.  I liken our standards to jumping over a one foot bar.   You and I know they are low!  I do have to agree regarding the piece of crap,  I looked at the advanced framing techiques link and 24" O.C. is worthy of that designation. You can't have an energy efficient house fall over in a tiny storm or simply keel over after 20 years.

Don't oversell ICF on thermal performance, since it's a loser from an R/$ point of view. (R-value IS R-value when looking at clear wall/whole wall numbers).  But it's a clear winner on several other fronts. Contrary to what you might presume from the tone of this and my prior post I'm all for it.  I'm just against selling the thermal performance aspects by misrepresentation & straw man arguments regarding other construction methods.  ICF has enough going for it without going there.

I don't think I am overselling ICF on thermal performance -- the actual r-value of your typical wall is what is in question here.  The "ingredients" of ICF are in series -- it's when things are in parallel that they get interesting.  I believe we agree on many points.  Contrary to how you might hear my tone,  I am 100% behind ICF and a 99% fan of your posts.   Regards.

In my opinion, if high thermal performance in a heating dominated climate combined with low cost are your top two priorities, then the double 2x4 wall assembly separated by at least 1 inch (including top and bottom plates) coupled with wet sprayed cellulose is the way to go. Then add as much exterior rigid foam insulation as your budget and exterior wall surface can tolerate.

I have a small section (~7'x12') of my ICF home envelop between the kitchen and 2x4 stick built garage that will be conventional wood frame construction. This is just a half bath and entry point for garage/kitchen/covered porch. I've went back and forth on how to build this small section. I considered double 2x4 stud, but I wanted to keep the wall closer in thickness to a 2x6 wall. What I have finally (right now, may change tomorrow) come up with is the following:

Starting with the exterior and working my way inward:

Brick veneer
1" air gap
1/2" rigid polyiso with fiberglass-cement facing for higher permeability (R3.0)
7/16" OSB for shear strength (~R0.5)
2x4 @ 16" oc with wet sprayed cellulose (~R10 - see previous discussion - HA!)
1" rigid polyiso with foil facer to inside (R6.0)
3/4" thick 1x4's ripped in half over every stud to provide 3/4" air gap for polyiso foil facing (R2.77 per ASHRAE)
1/2" drywall (~R0.5)
interior air film (~R0.7)

Total wall thickness (not counting brick or exterior air gap) = 0.5 + 0.5 + 3.5 + 1.0 + 0.75 + 0.5 = 6.75"

Whole Wall R-Value = 3.0 + 0.5 + 10.0 + 6.0 + 2.77 + 0.5 + 0.7 = ~R23.5 which is comparable to my ICF walls.

wow this turned interesting fast. THis was exactly the sort of responses I was trying to get at. My wall system I settled on (2' staggered 2x4 wall on 2x8 plates, 1-1.5" xps, ZIP sheathing, blown cellulose/fiberglass) should be quite a bit higher performing wall then the hobbs ICF in my heat dominate climate I think. It is also a smaller gamble for me to build, IMO has I have put up plenty of framed houses. I will still plan on ICF for the basement however. I just do not think the extra cost involved is worth it for the other advantages a lone. Energy is my biggest goal since I will be on all electric.

Wow - its hard to belief some people like math this much! Its a challenge to keep up with the numbers but I do find it very interesting. Thanks all!
Texas - you use R22 for the value of ICF. The gentleman who did my heat loss calc's for designing my Unico system (local rep for a national heating supplier) said he uses R50 for ICF (2.5 + 5 + 2.5). I thought that just a bit high. However as I posted earlier, I am presently heating around 5200 sq.ft. of space, Two floors have 9' ceilings and one has 8', with two 3000 watt heat elements in a water tank. (I think that is around 20000 btu's?) and hold within 3º of target (70ºF) with temps as low as -22F for the past four weeks. I believe our design temp. is -31C or -24F. This would lead me to believe for this climate, his assumption of R50 would be close. This does not agree with all the R's and U's in the preceding. Would you or the other gentlemen care to comment on this?
Bob

Posted By arkie6 on 16 Feb 2011 07:43 PM
Another consideration was the poor quality of building lumber today.  When just building the bracing for my ICF walls, I probably had to cull 1/3 of the 2x4s because they were too crooked or twisted.  And these were considered "premium" quality studs.

I swear 2 x 4s sensed when they were carried into the house while I was framing the interior walls. I'd pick out a nice straight stud from the package sitting outside the front door and by the time I got it on the miter saw inside the house it was a cork screw!!

Posted By lzerarc on 16 Feb 2011 10:32 PM
wow this turned interesting fast. THis was exactly the sort of responses I was trying to get at. My wall system I settled on (2' staggered 2x4 wall on 2x8 plates, 1-1.5" xps, ZIP sheathing, blown cellulose/fiberglass) should be quite a bit higher performing wall then the hobbs ICF in my heat dominate climate I think. It is also a smaller gamble for me to build, IMO has I have put up plenty of framed houses. I will still plan on ICF for the basement however. I just do not think the extra cost involved is worth it for the other advantages a lone. Energy is my biggest goal since I will be on all electric.

Why do you want 2x8 plates?

Posted By FBBP on 16 Feb 2011 11:32 PM
This would lead me to believe for this climate, his assumption of R50 would be close. This does not agree with all the R's and U's in the preceding. Would you or the other gentlemen care to comment on this?
Bob

You lucked out?????!!!!!!!!