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Unregistered
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Posts:2321
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| 02/17/2002 11:15 PM |
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Maybe this is more of a website mgmt issue...but it also begs the question of what I'm missing....
I followed the link on icfweb.com to the learning center and then the link for the whole wall R-value calculator. I ran the "standard house #3" thru the calculator with 4 walls types - ICF, SIP, 2x4 wood, steel studs. Here are the results:
2x4 studs
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16" O.C., 1/2" gypsum interior, loose cellulose, 1/2" plywood siding
Clear-Wall R-value = 10.81 h-sqft-degF/Btu
Whole-Wall R-value = 9.42 h-sqft-degF/Btu
SIP
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1/2" gypsum interior, 5/8" OSB inside and out, 5 5/8" EPS insulation between, 1/2" beveled siding exterior
Clear-Wall R-value = 24.72 h-sqft-degF/Btu
Whole-Wall R-value = 21.42 h-sqft-degF/Btu
ICF
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PolySteel, 1/2" gypsum interior, 1/2" stucco exterior
Clear-Wall R-value = 11.96 h-sqft-degF/Btu
Whole-Wall R-value = 10.29 h-sqft-degF/Btu
Steel Studs + Icynene
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16" O.C., 1/2" gypsum interior, 1/2" OSB over 1" EPS exterior, 1/2" wood siding
Clear-Wall R-value = 13.17 h-sqft-degF/Btu
Whole-Wall R-value = 9.26 h-sqft-degF/Btu
From this, it would seem that SIPs are the way to go - with a whole wall R-value TWICE that of the ICF!! Heck, the ICF isn't even that much better than 2x4 studs!? I hear of ICFs with R-values of 30, 44, even 50 - and I recognize that these numbers are 'fuzzy' - since they are trying to incorporate reduced infiltration + thermal mass - which technically don't figure into R-values (I think?).
Something seems amiss here?? I recognize SIPs are a good product - considering them for a current project - but something seems weird. If nothing else, if this website is designed to promote ICFs, I'd jetison this link - I'm not the only info-seeker out there that will run these numbers.
Interested to hear what folks think of this. |
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markross
Registered Users
Posts:1035
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| 02/18/2002 12:12 AM |
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The true measure of heat loss in testing is called the "hot box" test. The test is a practical test of applied heat and a measurement of the transfer of the heat through a wall. Calculated values mean little in the real world. In Canada, a 2x6 wood framed wall assembly, r-22 batt insulation, interior fully sealed vapour barrier and exterior moisture barrier thermally tested at a whopping Real R value of 17.8. A 6" concrete core ICF with 2.5 inches of EPS foam on both sides came in at a measly 34.7. Inside delta T was 68 degrees F and the outside delta T was -15 degrees F.
However, due to the nature of ICF construction the thermal performance of the wall assembly changes depending on climatic location. The closer to an even cyclic temperature, the better the overall R value. Or if your indoor temperature is 68 degrees, and your daytime high is 98 degrees with a nightime low of 38 degrees, then you are in the ballpart of R-48 real performance. However, as you go north, the real R value starts to drop, however so does a wood framed wall assembly. The lowest I have extrapolated is R-25+ in igloolik, Canada. Major cold there.
Hope this helps.
Mark Ross
"Le Canuck" |
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Unregistered
Registered Users
Posts:2321
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| 02/18/2002 12:28 PM |
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Mark,
Thanks for another great reply -
Some additional comments:
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If my understanding of the units used is correct, these values are 'per degree F' - not sure how that figures in.
In terms of procedures - the info on the calculator page indicates that this is in fact using a 'hot box' procedure - they have photos of the wall sections being built and tested. The detailed publication referenced also indicates use of the hot box. They then 'model' this - simply to scale that to a whole house system But the calcs are for the wall assembly.
Also, the performance of EPS drops due to lower temps - but the decline is not nearly as steep as with fiberglas batts. So that scores 1 for the ICF - but in terms of comapring ICFs to SIPs - the SIPs are still in the hunt as the majority also use EPS, correct?
Thanks again,
Keith |
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markross
Registered Users
Posts:1035
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| 02/18/2002 7:12 PM |
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Kieth.
First and foremost, ICF structures vrs sips is a call you have to make. sips represent a series of panels, which at each joint has the capacity or potential to leak air if not properly constructed. As well, they are subject to damage from water buildup. Structurally, the assembly is good, but not as good as an icf structure. one very heavy wind could, and I repeat that there is little chance but it could, cause enough flex to seperate joints. As for the decreasing energy efficiencies as we go north, has a lot to do with thermal mass, which is a topic for another day. Reality is sips dont have that thermal mass effect which buffers and stores the heat, which makes the ICF's more energy efficient. Do not rely on calculated R values, they are not accurate. Much like soils engineering, a lot is based on assumptions, so it is by far, not an exact science.
Nothing personal, but I would rather have a one piece structure and building envelope, than one made up of parts and pieces. Your call.
Mark Ross
"Le Canuck" |
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Unregistered
Registered Users
Posts:2321
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| 02/18/2002 8:25 PM |
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Mark,
I agree - a one piece envelope seems logically better - no question about that!
I also agree that having the thermal mass makes sense - one can do the BTU/heating load calcs - and look at the 'storage' capacity of the concrete - this points to a more stable environment. BUT - in terms of 'R-values' which are used by the building industry 99.5% of the time - concrete doesn't fare well. We can discuss the need for other measures til we're blue in the face too!
As I said at the top of my post - maybe this is just a website mgmt issue - if nothing else, maybe this isn't the best link (the one to the calculator) to have on a site interested in promoting ICFs - someone unwilling to dig deeper would take the results at face value and conclude that ICFs are all hype. OR....someone wanting to poke holes in the quality of the ICF products could certainly have fun pointing to the 'funky' results of the calculator found on the 'ICF industry's' own promotional website - it simply isn't a great marketing tool for ICFs (IMHO).
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jdcoombs
Registered Users
Posts:57
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| 02/19/2002 10:20 AM |
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Some good points here. I *really* get flustered on this stuff. Mostly because there is so little in the topic that is defined. It's, to a great extent, very subjective. I didn't even know the calculator was there; and now that I do, I can say I'm duly unimpressed. I don't purport to completely understand what's going on in the "calculator" (It really appears to be a database) but I'll correct that as soon as possible. If anyone has any information that can help clear up this section please pass it on.
At this point I'm a little tentative at the results, but that's my nature. But if one is to use this tool, use caution and keep a few things in mind:
-According to the section, the results are partially based on a mathematical model (ill-defined) and partially on the hot-box (also ill-defined)
-There are truly too many variables in a system like this to define it with either a test or a model
-There is *NO WAY* in a closed system, that two, 2-1/2" thick (using a flat-wall for ease of discussion) pieces of EPS separated by ANY material will have a lower R value than 4" of solid EPS, once it reaches equilibrium.
-R-value is a simplified statement of a static property (heat transfer) of a material. It doesn't lend itself well to the complex issues of a dynamic system like this.
-ICFs have been around long enough to prove themselves in the utility bills, regardless of think-tank supposition.
American Polysteel has done additional third-party testing that has significantly different results that those shown.
And aside from the R-value issue, as Mark pointed out, there are several other good reasons to use ICFs over SIPs. I think that SIPs are a great second choice :)
Jerry D. Coombs, PE
Director of Engineering
American Polysteel, LLC
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ICF372
Registered Users
Posts:219
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| 02/19/2002 9:04 PM |
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All good points. When we did our last home show the sips booth next to us advertized the same energy savings as we did. But we both compared our systems to stud walls. Not icf to sips. Maybe its time? We are building a icf promo. home, I would be glad to give our plans to a sip builder and have them tested. Let the games begin. Will there be much differance probably not much. But when you look at maintaince over the 200+++ years icf's will win out, both structurly and enviormently.
Eldon Howe |
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Eldon Howe
Howe Construction
Total Concrete Homes provide positive cash flow , DAY ONE . |
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