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Hello, background, situation, and conflicting info on ICFs?
Last Post 27 Feb 2011 12:54 AM by dmaceld. 149 Replies. |
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pura vida
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| 08 Feb 2011 09:21 PM |
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Posted By ICFHybrid on 08 Feb 2011 07:23 PM
Are you considering hydronic slab heating for the garage?
please excuse my ignorance, i have seen this mentioned but i'm not sure what it is? radiant in floor heat? if so, that was the plan. probably with a free standing wood stove as supplemental. i was considering doing it myself, and still am but with the size of the project it makes we a little nervous. the contractor i have been talking to has really been pushing the diy thing to help me save on cost. i could tell he was a little hesitant to tell me the final cost over the phone :) think he was concerned about my reaction. i'll have to see what the breakdown is tomorrow when i meet with him. that will really give me a better understand of what i have to work with. if i could get it to the 60k mark i would probably seriously consider it. we will see. concrete is expenisve up here b/c it has to be shipped up from the lower 48. i saw quoted prices around 125-130 per yard. i think he said there was 208 yards in my walls as it is now. that's over 27k just in concrete... |
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TexasICF
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Posts:622
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| 08 Feb 2011 10:04 PM |
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mmmm. Somethings a bit off. If you have 6K square feet of wall. How thick is your wall? Six inch is 111 yards or about 15K big difference. Eight inch would be about 146 yards or about 19K. Looks like your building your house out of 12" concrete. BTW we've gone 8 stories with load bearing 6 inch concrete core. I may be missing something but you might want to consider building to just 10x stronger than conventional and bypass the 30x particularly if it seems expensive. Regards. |
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lzerarc
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Posts:423
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| 08 Feb 2011 11:09 PM |
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Looking at my more final numbers, depending on if I pay an insulator to blow in the fiberglass, which I really would like to do, prices out to be the same price as Hobbs DIY full house. There has been a lot of talk about the mass of ICF slowing down the temp swings, however how does the Hobbs system come in the play? They are about 9", and the concrete thickness varies greatly over the length of a wall. Around windows, at the base and top of the wall, its 6". However it can be as thin as 2" of concrete with 7" of EPS. They boast about saving a lot of concrete and replacing it with "higher r foam"...but is this almost defeating the purpose of ICF walls.
Would TF ICF be a better soluation? I really like the support Andrew Hobbs has been giving me and is just a couple hrs away. He said he would come up and personally help set the basement with me. |
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pura vida
New Member
Posts:41
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| 08 Feb 2011 11:31 PM |
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texas - tomorrow night i should have a better handle on it. let me get the numbers in front of me and then i will post the details. i was just repeating what i could remember he told me. i could easily have the numbers wrong or have mis-understood |
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TexasICF
Advanced Member
Posts:622
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| 09 Feb 2011 10:27 AM |
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Izerarc, Since you're asking here are some things to consider.
-- If you are close to the same price then I suppose that decision should be an easy one.
-- Hobbs has a bit less mass but I don't think it is significant enough that it should weigh heavily on your decision.
-- Your biggest challenge with this type of system will be proper consolidation (internal vibration). This needs to be done properly.
-- They do save quite a bit of concrete and do replace it with higher r-value foam. Their R-value is actually about the same as a typical ICF. For the same reason the r-value of spray foam and studs is compromised 'strongly' by the stud -- these systems actual R-value will lean a bit toward their weakest link -- e.g. where the concrete is thickest. In other words you can't average the r-value for the thick foam areas any more than you can ignore the studs in a wall. See R-U vindicated article in ICF builder magazine. If this doesn't make sense -- imagine the following hypothetical block -- solid foam 9" thick separated by 2" wide concrete pilasters that are 9" thick. Average r-value would be very high but actual r-value would be very low.
-- Regarding switching to TF. The vertical guys maintain that these systems are easier, faster and etc. Having completed over a million square feet myself of standard ICF I don't believe this to be the case. If Andrew Hobbs is going to personally help you set up your basement I would stick with him. Regards.
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lzerarc
Basic Member
Posts:423
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| 09 Feb 2011 12:22 PM |
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thanks for the article, it was interesting. I talked with Andrew for some time this morning about u values and things of that nature. Do you know of any resource that shows how these u values can be taken into account for hvac loading and stuff like that?
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TexasICF
Advanced Member
Posts:622
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| 09 Feb 2011 12:51 PM |
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Izerarc, The shortest answer to your question is no. Most of the tonnage calculation programs are written by and provided by the HVAC companies. Unfortunately, this means that you can have a house that requires less tonnage and the program will tell you to use basically the same tonnage. You can test this by putting in R-gazillion and etc. and seeing what the program does. The biggest problem i've had in the ICF industry is AC guys insisting on overtonning. Over tonning is much more serious than undertonning because your system will quickly hit the set point and turn off, short cycle and never reach dehumidification cycle. I've usually found that ICF coupled with good windows and a foamed attic translates into about 1/2 the tonnage. Of course this is just a guess and you would want to run your design by an expert. Typical tonnage for conventional construction is 450-500 square feet per ton (Texas). Most ICF houses with good attics here (Texas) are designed to about 1000 square feet per ton. I run mine at close to 2000 square feet per ton. I actually, have enough tonnage to cover 1000 square feet per ton but have electronically disabled my second stage so my system stays permanently in stage one.
Another point to remember about todays AC is that todays systems are much smarter e.g. multi-stage (even 3 stage geo). What this means is that you can be way overton (and thus buy more tonnage than you need) and not be hurt by the overtonnage. That if you have a system that never turns on your second stage you are overtonned (in my opinion). For my next house, let's say 2K square feet. I would want two multi-stage one ton units and one of them would rarely come on at all.
This is how we've made some progress with engineers that think that ICF won't get you there. If you have a library that normally gets 10 tons - you will be doing everyone a favor if you use 2 multi-stage five ton units. Your conservative bases are covered and the system will run on stage one of one unit most of the time.
Another quick point from the article - is that it is really everyone else that is claiming more R-value than they really have (meaning conventional stick). ICF has a true R-value because heat flow is perpendicular to uniform panels. e.g. foam, concrete, foam. Regards. |
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lzerarc
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Posts:423
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| 09 Feb 2011 02:55 PM |
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We are heating dominate here obviously, with around 7200 HDD if my memory serves me. Based on my r30 stick frame design, my heating load for the 2800 sqft house (including walkout basement and main floor) is right around 30k BTU. Geo designers I am talking with are giving me 2 options basically. Do do a full 3 ton system with 10kw backup strip, which will cost around 24,000 (including HRV and some other items) that has a BTU of around 32k at full load. They also have a 2 ton option with a 10kw heatstrip that runs at 19k BTU full load. This would cost around 21,000. I guess I would be curious if ICF would cut the infiltration and everything enough to actually drop that 30k BTU load even more. It is hard to really figure out the sizing for something like this. I am guessing that the safe bet would be the 3 ton system. However as you mentioned, cooling with the 3 ton, for our area, is WAY over sized. Both options are 2 stage w/ desuperheaters. |
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dmaceld
Veteran Member
Posts:1465
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| 09 Feb 2011 04:36 PM |
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Posted By lzerarc on 09 Feb 2011 02:55 PM
We are heating dominate here obviously, with around 7200 HDD if my memory serves me. Based on my r30 stick frame design, my heating load for the 2800 sqft house (including walkout basement and main floor) is right around 30k BTU. Geo designers I am talking with are giving me 2 options basically. Do do a full 3 ton system with 10kw backup strip, which will cost around 24,000 (including HRV and some other items) that has a BTU of around 32k at full load. They also have a 2 ton option with a 10kw heatstrip that runs at 19k BTU full load. This would cost around 21,000. I guess I would be curious if ICF would cut the infiltration and everything enough to actually drop that 30k BTU load even more. It is hard to really figure out the sizing for something like this. I am guessing that the safe bet would be the 3 ton system. However as you mentioned, cooling with the 3 ton, for our area, is WAY over sized. Both options are 2 stage w/ desuperheaters.
The challenge you are dealing with is the 30k Btuh is an instantaneous, so to speak, heat load. In other words that's the heat load at the minimum design outdoor temperature and is something like the temp that historically is exceeded only about 3% of the time. Most of the time your instantaneous heat load will be a lot less than than that. For an interesting exercise find and download a ten year history of hourly temps for your area and do a spread sheet analysis to find out what temp your area is like 80% and 90% of the time. If that temp is significantly above the Manual J design temp then consider sizing the heat pump for that temp recognizing that below that temp it will run 100% of the time and need auxiliary heat also. If you have a fairly wide daily temp swing an ICF wall will average out that swing and the instantaneous heat load will be less. One thing you can do is install a buffer tank in the system and feed your heating and cooling piping from there. That way you can have an oversized heat pump but feed heat into the living space on an as needed basis continuously without the highs and lows caused by the heat pump turning on and off. Whatever you come up with the goal is to feed heat into the living space equal to the instantaneous loss to the outside. A variable heat supply will do that. I have a Daikin air-to-air heat pump with a variable speed compressor. My house stays within about 1/2 degree of the set point, except when solar heat pumps it up in the living room. In practicality all of this data massaging may not make any difference simply because of what's available in heating equipment. And you need to have an HVAC contractor who can grasp these concepts and work with them. I'm doubtful average Joe Blow furnace installer will. There is a program called HEED from U of Cal, or somewhere out there, that will show you heat loads on an hourly basis. It's free. If you are into such things get it and make some calcs with it. |
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| Even a retired engineer can build a house successfully w/ GBT help! |
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lzerarc
Basic Member
Posts:423
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| 09 Feb 2011 05:49 PM |
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My locat utlitiy actually gave me a spread sheet that is pretty cool. They are really pushing energy efficient stuff, and have pretty good incentives as well. The spread sheet has me enter the BTU requirement for the house, COP for the geo and its capacity (to figure aux heat), cost of electric rate, then you can also compare ASHP w/ elec aux backup, furnace backup, or staight gas furnace for yearly heating costs. It takes a 10 year average of the temps in my specific area and says there was 771 hrs at 67 degrees, 112 hrs at 12 degrees, etc, for every 5 degrees between -23 and 67. With this it also breaks down the Kwh used by both the aux and geo hp during each of these hr blocks. So you can clearly see the aux kicking in after it passes the geo output capacity. You can qucikly enter 19k (for the 2 ton) or 32k for the 3 ton and see the cost difference it gives you in electric backup. As you stated, the peak loads where it is using a lot more aux is very small in the entire course of the year, and its giving me a $90 difference between the 3 ton and 2 ton for cost. This is at 30k btu heat requirements. If ICF reduces that to say 26-27k, then that number reduces even more. I am really leaning towards the 2 ton at this point.
According to the chart, heating hrs below 0 on the 10 year average is about 90 for our area, and below 32 degree is about 1732.
I will check out the HEED for sure, thanks. |
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dmaceld
Veteran Member
Posts:1465
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| 09 Feb 2011 07:14 PM |
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Posted By lzerarc on 09 Feb 2011 05:49 PM
My locat utlitiy actually gave me a spread sheet that is pretty cool. They are really pushing energy efficient stuff, and have pretty good incentives as well. It's hard to love a power company, but it sure sounds like yours comes close!  I can hardly believe they're giving you that much good information. You're fortunate, IMO. |
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| Even a retired engineer can build a house successfully w/ GBT help! |
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lzerarc
Basic Member
Posts:423
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| 15 Feb 2011 08:56 AM |
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question on electrical in ICF....how are the boxes attached? Do you have to use metal boxes and tapcon them to the concrete? or can you use plastic boxes with a side mount face and screw it to the plastic studs?
I am still not 100% convinced on full house ICF for our climate. It seems every study I have read, from ICF mag, to building science, etc, seem to not really recommend ICF for cold climates. It would appear that the only real benefit I would get is the added strength and an easier air barrier. It does not appear I will have an benefits of the internal mass, at least during the winter. Looks like I would be sitting on an r-24ish wall for 75% of the year. Some studies I have read recommend higher r and well sealed wall assemblies vs ICF (so thicker SIPs, double stud wall, etc) Is this a correct assumption? |
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FBBP
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| 15 Feb 2011 09:38 AM |
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Posted By lzerarc on 15 Feb 2011 08:56 AM
question on electrical in ICF....how are the boxes attached? Do you have to use metal boxes and tapcon them to the concrete? or can you use plastic boxes with a side mount face and screw it to the plastic studs?
I am still not 100% convinced on full house ICF for our climate. It seems every study I have read, from ICF mag, to building science, etc, seem to not really recommend ICF for cold climates. It would appear that the only real benefit I would get is the added strength and an easier air barrier. It does not appear I will have an benefits of the internal mass, at least during the winter. Looks like I would be sitting on an r-24ish wall for 75% of the year. Some studies I have read recommend higher r and well sealed wall assemblies vs ICF (so thicker SIPs, double stud wall, etc) Is this a correct assumption?
Izerarc - with regard to electrical, we just cut out the box opening with a router or electric chain saw, do our wiring and push the box in. If it is springy or won't stay straight, we might insert a nail or screw into the foam to hold it. We than give it a light application of foam between the box and the icf and we're done.
With regards to cold climate. I have not yet moved into my house which is 1400 on two floors, 1400 of walk out basement and 1000 ft over the garage plus the garage. Floor slabs are in with hydronic pex pipe installed. I am heat the house comfortably right now with on 40 gallon electric hot water heater with both 3000 watt elements activated. We are just outside Calgary Alberta and have been experiencing "mood" swings from minus 35ºC to plus 10º over the past five weeks. If it was not for all the windows and doors we have ( 40 averaging over 5' x 5') it would be even easier to heat. There may be other forms of construction that can match that but will they still be that well sealed in five years?
I can not think of a single reason that I would use anything but ICF for my next house.
Bob
p.s. no this is not my final heating system and neither do I recommend a water heater for long term hydronic heating. |
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lzerarc
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Posts:423
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| 15 Feb 2011 03:16 PM |
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FB: does that mounting type meet code? (assuming your is the same as ours...IRC)
Also what kind of block/thickness did you use? |
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TexasICF
Advanced Member
Posts:622
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| 15 Feb 2011 06:54 PM |
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I like tapcon to concrete whether plastic or metal boxes. Regarding cold climates and ICFs - please point me to some of these studies. The only one I am aware of is the often misquoted ORNL study on thermal mass. For example, this study says that thermal mass in Minnesota only adds about 8% improvement in performance over conventional systems built to the same r-value. The problem with this is that conventional systems are not built to this standard or r-value. See latest article in ICF Builder magazine called R-U Vindicated? Regards. |
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lzerarc
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| 15 Feb 2011 10:30 PM |
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Yes, I have read it several times. To my understanding, the lower the u, the better. It also states concrete has a u of 10! It goes through the calcs for the studs, but is not really clear how they are showing the ICF is far above it.
if you use their math and numbers, take a 6" concrete wall with 2 2.5" layers of EPS...r4/inch, so r20 there. 1/20= u of .05. x45% (of wall)= .0225 u value of foam.
Now take the concrete, which has an r of .1 it says. so 6x.1= .6 r value. 1/.6= 1.6 u value. times that by 55% of wall, equals .912 u value. .912+.0225= .939 total u. this does not make any sense...what I am doing wrong?
I have done a lot of searches, and do not have time to dig them up again. There was certainly more then 1 that mentions pour (at foam's r value) performance (excluding infiltration as that can be comparable with other systems without mass). But this is one I remembered reading:
http://www.buildinggreen.com/auth/article.cfm/1998/4/1/Thermal-Mass-and-R-value-Making-Sense-of-a-Confusing-Issue/ |
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dmaceld
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| 15 Feb 2011 11:41 PM |
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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 |
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| Even a retired engineer can build a house successfully w/ GBT help! |
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dmaceld
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| 16 Feb 2011 12:01 AM |
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Posted By TexasICF on 15 Feb 2011 06:54 PM
I like tapcon to concrete whether plastic or metal boxes.
Seems to me like I came across info in the code, or somewhere, that a metal fastener inside a plastic box is not kosher unless there is provision built into the box for a metal fastener. Basically that means a hole in the bottom of the box with a raised cylinder around it to keep wires from coming into direct contact with the screw head, like what you see on plastic ceiling boxes mounted on hanger bars. For my outdoor fixtures I used those boxes. I discarded the hanger bar and put a tapcon through the screw hole. Realistically, the restriction of a metal screw head inside a plastic box is somewhat excessive, and if the inspector doesn't complain then you're OK. |
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| Even a retired engineer can build a house successfully w/ GBT help! |
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lzerarc
Basic Member
Posts:423
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| 16 Feb 2011 08:53 AM |
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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....... |
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TexasICF
Advanced Member
Posts:622
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| 16 Feb 2011 09:53 AM |
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http://www.icfmag.com/articles/feat..._code.htmlHere's the article. The article doesn't say the the R-value of ICF is high nor is thermal mass considered in any way by the article or by R-value itself. What the article does say is that viturally the whole world (construction industry, home depot, architects) typically claim wall R-values much higher than they really are. The r-value of ICF cannot be disputed because to someones point above heat flow is perpendicular to the materials: R-foam + R-concrete + R-foam = R-ICF . When two or more different materials are parallel to heat flow -- e.g. studs of wood and foam or metal studs and foam etc. you can not just say that the R-value of the wall is whatever the foam cavity is as most builders do. Or the average of the stud R-value and the foam R-value as many architects do. If you really care about not kidding yourself you need to use the appropriate equation for different materials that are in parallel to heat flow. Another way to look at this is if we did a test with a (hypothetical) solid metal 2x4" with an r-value of practically zero virtually all the heat would ignore the foam or whatever and flow through the stud. If the foam was r-100 the wall would still have an r-value of something close to zero because all of the heat prefers to go though the path of least resistance -- the stud. Now if you make the foam r-1000 nothing changes you still have an r-value close to zero. I should say nothing changes for the R-value who knows what the builder or architect might claim. Regards. |
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