Need help choosing ICF vs SIP
Last Post 02 Jul 2011 09:48 AM by lightfire. 29 Replies.
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tsriddleUser is Offline
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09 Feb 2011 08:33 PM
Hello all, I've been reading for weeks and I still can not decide.  Here is a little back ground on what is being planned:

2700 sq ft two story house in Lubbock, Texas
Average temps range from the mid 90's in the summer to the mid 20's in the winter (often temps get much higher and much lower).
17-18 inches of rain (humidity is low)

Leaning towards SIPS but the following factors may swing my decision.  1)  Lubbock is in tornado alley and I like the idea of concrete walls.  2) For whatever reason, Lubbock seems to have allot of ICF contractors.

I like the idea of the SIPS and I'm not sure the thermal mass aspect of ICF out weigh the R value of SIPS.

Any ideas would be helpful.
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09 Feb 2011 10:15 PM
Posted By tsriddle on 09 Feb 2011 08:33 PM 
  1)  Lubbock is in tornado alley and I like the idea of concrete walls. 
then use SIPs on roof
Chris Kavala
info@southernsips dot com
1-877-321-SIPS
FL. Lic # CBC036455, GA Lic. RLCO000624, LA Lic. # CL33845
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09 Feb 2011 11:49 PM
Here's a link to a story you may find interesting. This is a SIP home in TN that did rather well through a hurricane (however the foundation did not fare well).

http://www.noarkrcontrol.com/SIPs/projects/TN-Tornado.asp
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10 Feb 2011 10:50 AM
Just in case your budget is too limited for ICF's, some metal skinned SIPS are rated up to 150 MPH +.  However, that may be fine for hurricanses, but may be a little shy for tornadoes.
Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
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10 Feb 2011 11:34 AM
Tsriddle,

I certainly understand your quandary. Here’s a couple of things that may help you make a decision. First of all, I believe that ICF’s make great foundation walls. They are strong and are much better insulated than a poured or block concrete walls. Like you, I’m not convinced with the thermal mass argument. In my opinion, make the best insulating envelope you can, and then place the thermal mass within the envelope to help maintain the ambient temperature. Think about a cooler with a chunk of ice in it. While, as you stated and I agree, ICF’s make a stronger wall, but are not as energy efficient. A standard SIP home is just about twice as strong as a standard stick built home. One of the reasons for this is in a stud wall, they put sheathing on the outside of the studs to prevent “racking”. Without the sheathing, you could almost easily push the top corner of the stud wall, and the whole wall would collapse. With a SIP wall, there is OSB glued to both sides, and over the whole area of the wall, gives it great strength. In other words, the sheathing is connected to the studs by nails every 16 inches on a stud wall, but glued over the whole area on both sides on a SIP wall. For added strength, a SIP home can be engineered and built to withstand winds up to 200 mph.

This is a quote from the R-Control web site http://www.r-control.com/strength.asp "Q. HAVE R-CONTROL SIPs BEEN PROVEN STRUCTURALLY IN EARTHQUAKES AND STORMS? A. Yes. R-Control SIPs have exceptional strength to resist seismic activity and high winds. R-Control has documentation of homes which used R-Control SIP’s that withstood the 7.2-magnitude earthquake in Kobe, Japan in January 1995. These homes were located just miles from the quake’s epicenter and stood solidly against the tremendous force of the earthquake. R-Control SIP structures have also withstood tornados in Tennessee and straight line winds and tree trunks crashing into them in Michigan."
 
The other weak point of a house is the roof. Once the roof blows off, it seems that the walls are next. If the roof stays intact, the walls seem to survive. A SIP roof can be connected strongly to a SIP wall with long screws, but I’m not sure how to strongly connect the roof to a thin concrete wall as in an ICF wall. Here’s another thing to think about. While a SIP home is almost as strong as an ICF home, I think a SIP home will be less expensive, better insulated and go up much faster. Please let us know what your final decision is.

Steve
GrandCountySIPs.com
Steve Etten
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10 Feb 2011 12:16 PM

tsriddle,

Two things to consider about SIPS:

1.  Metal skinned polyurethane filled SIPS are thinner than EPS SIPS with same R-value.

2.  Some SIP companies are now using treated OSB for EPS filled SIPS.

E-mail me if you need contact phone numbers.

Note:  I do not sell any products nor accept commissions from any company.  In most cases, I donate my free time to assisting with interesting projects that use alternative building technology. 

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu, 334 826-3979
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10 Feb 2011 12:58 PM
Posted By trigem1 on 10 Feb 2011 11:34 AM
Tsriddle,

I certainly understand your quandary. Here’s a couple of things that may help you make a decision. First of all, I believe that ICF’s make great foundation walls. They are strong and are much better insulated than a poured or block concrete walls. Like you, I’m not convinced with the thermal mass argument. In my opinion, make the best insulating envelope you can, and then place the thermal mass within the envelope to help maintain the ambient temperature. Think about a cooler with a chunk of ice in it. While, as you stated and I agree, ICF’s make a stronger wall, but are not as energy efficient. A standard SIP home is just about twice as strong as a standard stick built home. One of the reasons for this is in a stud wall, they put sheathing on the outside of the studs to prevent “racking”. Without the sheathing, you could almost easily push the top corner of the stud wall, and the whole wall would collapse. With a SIP wall, there is OSB glued to both sides, and over the whole area of the wall, gives it great strength. In other words, the sheathing is connected to the studs by nails every 16 inches on a stud wall, but glued over the whole area on both sides on a SIP wall. For added strength, a SIP home can be engineered and built to withstand winds up to 200 mph.

This is a quote from the R-Control web site http://www.r-control.com/strength.asp "Q. HAVE R-CONTROL SIPs BEEN PROVEN STRUCTURALLY IN EARTHQUAKES AND STORMS? A. Yes. R-Control SIPs have exceptional strength to resist seismic activity and high winds. R-Control has documentation of homes which used R-Control SIP’s that withstood the 7.2-magnitude earthquake in Kobe, Japan in January 1995. These homes were located just miles from the quake’s epicenter and stood solidly against the tremendous force of the earthquake. R-Control SIP structures have also withstood tornados in Tennessee and straight line winds and tree trunks crashing into them in Michigan."
 
The other weak point of a house is the roof. Once the roof blows off, it seems that the walls are next. If the roof stays intact, the walls seem to survive. A SIP roof can be connected strongly to a SIP wall with long screws, but I’m not sure how to strongly connect the roof to a thin concrete wall as in an ICF wall. Here’s another thing to think about. While a SIP home is almost as strong as an ICF home, I think a SIP home will be less expensive, better insulated and go up much faster. Please let us know what your final decision is.

Steve
GrandCountySIPs.com

the mass is more of a buffer than a holder of energy like would be required in a solar home. As different air temps pass through the eps, both sides of the concrete heat or cool.  Since it is dense, it takes time for the temp to pass through the concrete. Since temps are constantly changing on the exterior, this slows down the transmissions and levels the interior air temps.  Also not only are ICF stronger, but they are more air tight then SIPs. SIPs are only as tight as the caulking between every 4' joint and sills.  ICF, especially if used continuous from footing to roof (suspend your floor structure from it) gives you a 100% air tight shell.  Also, throw out R values and never look at them again when comparing ICF to whatever.  Compare U values...the results are amazing.  Besides, back to R...a basic ICF form and easily match the r of a 4" eps sips.  Just like SIPs can be adjusted in insulation values, so can some ICF forms.
Both are good products however, and I really do not think you can go wrong either way.
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10 Feb 2011 02:40 PM
the mass is more of a buffer than a holder of energy like would be required in a solar home. As different air temps pass through the eps, both sides of the concrete heat or cool. Since it is dense, it takes time for the temp to pass through the concrete. Since temps are constantly changing on the exterior, this slows down the transmissions and levels the interior air temps. Also not only are ICF stronger, but they are more air tight then SIPs. SIPs are only as tight as the caulking between every 4' joint and sills. ICF, especially if used continuous from footing to roof (suspend your floor structure from it) gives you a 100% air tight shell. Also, throw out R values and never look at them again when comparing ICF to whatever. Compare U values...the results are amazing. Besides, back to R...a basic ICF form and easily match the r of a 4" eps sips. Just like SIPs can be adjusted in insulation values, so can some ICF forms.
Both are good products however, and I really do not think you can go wrong either way.


While I agree that both are good products, I think each has it's own place and works better in separate applications. I wouldn't recommend SIP's for foundation walls, and would recommend ICF's in a noisy area. I assisted with a ICF house that was right beside a train track, and it worked very well.

With concrete having a very low R factor, it's difficult to see how it can slow down the transmission of heat or cold. And as far as ICF's being more air tight, I'm not sure I agree with that either. When I'm on site assembling panels, I make sure that all four sides of the splines are sealed with a bead of sealant. The base board (that the panel sits on) is glued and screwed to the subfloor, thereby eliminating leaks. The envelope is not just the walls, but windows, doors, foundation and roof. All aspects of the envelope must work in co-ordination with each other to achieve the highest efficiencies. As far as U values, I haven't seen any comparisons, so it's difficult to make any judgement about that. I would like to see three houses built, stick, SIP and ICF, side by side, with the thermostats set at the same temperature for a year, and then compare the cost of heating and cooling.

According to the Oak Ridge National Laboratory ( http://www.ornl.gov/sci/roofs+walls/articles/WallRating.html) the ICF whole wall R-value is 15.7 and the 6 inch SIP wall has an R-value of 21.6. Now if R-value stands for the resistance to heat loss, SIP's have an almost 50% higher resistance to heat loss than ICF's.

Steve
GrandCountySIPs.com
Steve Etten
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10 Feb 2011 05:09 PM
I am a big supporter of both products, and both are great. Had my SIPs suppler closer to home not closed its doors recently, I would be using urethane sips above grade, ICF below for my new house.  However since then I have done FAR more research on ICF.  I too never believed the the thermal mass, lower R etc etc etc.  However like I mentioned, r can not be compared for wall structures any more.  Energy code is moving toward using u values instead of r because they can be flawed by so many factors.
Remember, R only pertains to the resistance of a specific product.  U is the total performance of the wall, taking into account conduction, air movement and resistance. 
Check out this article for more about u in walls.  they use frame walls, but you get the point of the example.

http://www.icfmag.com/articles/features/ru_vindicated_energy_code.html

SIPs can be a very tight structure.  But like I said its only as good as the installer and caulk joints.  I trust you and many other installers are very conscious of this importance, but many are not.  With ICF, the interior is a continuous pour without any caulk joints.  To me, this sounds like a more failproof design.

But I agree, several homes should be built and tested.  I recall seeing a show on DIY network or HGTV about a place that built several and were testing them heavily.  i do not recall the location or name.
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10 Feb 2011 07:19 PM
Ok, I read the article (several times) and here's what I've geaned from this. The higher the U-value, the lower the R-value. I looked it up elsewhere and it was defined as this :
"The U-value is the inverse of the R-Value; i.e. you divide 1 by either the R or U value to convert to the other unit. So as the R-Value goes up the U-Value goes down and as the R-Value goes down the U-Value goes up. So the U-Value is a measure of how well a material transmits heat.
For instance a substance with an R-Value of 2 has a U-Value of 0.5 = (1 divided by 2)."
If this is correct, then there is a direct mathamatical relationship between the R-value of a substance and the U-value of the same substance. Just a differnt way of stating the same thing. The higher the R-value, the better, the lower the U-value, the better. Note that the article stated that concrete was a U-value 10 per inch, and EPS foam was 0.20. I think I'd go with the EPS, a 50 times better insulator then concrete.

See http://www.ecowho.com/articles/22/What_is_R-Value,_U-Value_and_how_do_they_relate_to_insulation?.html

Look at it this way. It's 20 below outside and 70 inside and you have ICF walls. The heat moves slowly through the EPS foam (good insulator), moves quickly through the concrete (poor insulator), then slowly through the EPS foam. EPS foam is a poor heat conductor and concrete is a good heat conductor.

BTW, this has been a very interesting conversation. I try to keep an open mind and I'm always interested in learning something new.

Steve
GrandCountySIPs.com
Steve Etten
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10 Feb 2011 10:02 PM
Steve, here's my two cents, and I really don't disagree with you much. You said: "Note that the article stated that concrete was a U-value 10 per inch, and EPS foam was 0.20. I think I'd go with the EPS, a 50 times better insulator then concrete."

Poured concrete has an R-Value of about 0.08, and EPS foam is about 3.00... that yields a ration of roughly 37.5, where EPS is much better insulation than concrete. That the concrete in ICF is sandwiched between two 2.5" sheets of EPS, though, does mean that when temp inside drops below the temperature of the concrete, some of that thermal energy will migrate back to the inside of the structure. But, since we are talking heat loss here (ie. winter time), then the outside is going to still be colder than the indoor temperature, so the majority of the thermal energy in the concrete will still migrate to the outside of the structure, but some of it can and will migrate back to the inside.

If I were designing ICFs, I would at least try come up with a way to move the foam all to the exterior of the structure, and the concrete to the interior. That would probably entail some kind of foam wall on the outside, and a removable form on the inside, and all of the associated problems that such a product would entail. What that would buy you, though, would be true thermal storage on the interior of the structure, and the minimum possible thermal migration to the exterior.

That large thermal mass on the interior of the structure would also present the problem that when it cools, it would take a substantial amount of thermal energy to heat it back up to a comfortable temperature. Where a large interior thermal mass makes most sense is with passive solar heat gain... short of that, all of the rest of this discussion is relatively moot, since that much concrete probably isn't the best use of capital since it is only real benefit is structural support.

And on your other comment: "the ICF whole wall R-value is 15.7 and the 6 inch SIP wall has an R-value of 21.6. Now if R-value stands for the resistance to heat loss, SIP's have an almost 50% higher resistance to heat loss than ICF's. "

21.6% / 15.7 = 1.38, so it is actually closer to 38% higher resistance. And the fact that some of the thermal energy from the concrete would migrate back into the home, it might drop to 30% or possibly even lower. And if you factor in the thermal bridging associated with splines or metal tracks, then it could drop even more - so minimizing thermally bridging components for SIPs becomes important. But even with the more realistic value, and with all other things (like cost, and above/below grade) being equal, I would opt for the higher degree of insulation (at least above grade) that the SIPs afford.

I also like the idea of SCIP construction, because you almost get the best of both worlds, namely thermal storage inside, and a larger and solid block of foam insulation between the interior thermal storage, and the exterior concrete shell. At first I wondered about the thermal conductivity of those strut wires going through the foam and causing something of a thermal bridge to the exterior. But a couple of years ago, I ran the calculations and the thermal bridging really isn't that significant. My calculations, though were based on 10 gauge wire, and 6" spacing... I know that some systems today use 3/16" rods, and spaced further apart, so I am not certain that my initial calculations would reasonably mimic the newer systems.
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10 Feb 2011 10:53 PM
Posted By trigem1 on 10 Feb 2011 02:40 PM


According to the Oak Ridge National Laboratory ( http://www.ornl.gov/sci/roofs+walls/articles/WallRating.html) the ICF whole wall R-value is 15.7 and the 6 inch SIP wall has an R-value of 21.6. Now if R-value stands for the resistance to heat loss, SIP's have an almost 50% higher resistance to heat loss than ICF's.

Steve
GrandCountySIPs.com

Note that the ICF quoted in that link (System 6) was "EPS block-forms poured in place with concrete, block walls 1-7/8-in. (4.8-cm.) thick."  I am not aware of any ICF manufacturers today that use 1-7/8" thick EPS for the forms.  Most use 2-1/2" or 2-5/8" thick Type II EPS (R = 4.0 / inch @ 75F).  This yields a total wall EPS thickness of 5" to 5.25" with a total R value of 20.0 to 21.0.  A few ICF manufacturers offer 2" and 2.5" thick EPS forms with the higher density Type IX EPS which has an R value of 4.2 / inch @ 75F (4 inches x R4.2/inch = R16.8, 5 inches x R4.2/inch = R21).

The 6 inch SIP wall (System 11) also included plywood exterior and gypsum board interior in the total wall R value.  No mention was made of any interior or exterior applied to the EPS block forms.  This would add ~0.5 to 1.0 to the total wall R value.

So, 5" to 5.25" of higher density Type II or Type IX EPS used by the majority of ICF manufacturers will result in roughly equal R value compared to 6" of the lower density Type I EPS typically used in SIP panels.  Plus you get the thermal mass benefit of the ICF.  This thermal mass benefit is not insignificant in a climate such as Lubbock, TX where the exterior temperature can and often does swing above and below the homes interior temperature.  The thermal mass tends to dampen out the highs and lows resulting in reduced HVAC operation.

http://www.ornl.gov/sci/roofs+walls...ating.html

http://www.epsmolders.org/PDF_FILES/C578%20Chart.pdf
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11 Feb 2011 11:31 AM
Posted By Torben on 09 Feb 2011 11:49 PM
Here's a link to a story you may find interesting. This is a SIP home in TN that did rather well through a hurricane (however the foundation did not fare well).

http://www.noarkrcontrol.com/SIPs/projects/TN-Tornado.asp

That was a tornado, not a hurricane.  If that had been an ICF home rather than a SIP home, it is unlikely the house would have been shifted off the foundation.
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11 Feb 2011 12:24 PM
Posted By trigem1 on 10 Feb 2011 11:34 AM
...A SIP roof can be connected strongly to a SIP wall with long screws, but I’m not sure how to strongly connect the roof to a thin concrete wall as in an ICF wall....

Steve
GrandCountySIPs.com

"to a thin concrete wall as in an ICF wall."  Huh?  Most ICF walls used today have a 6" thick concrete core with an overall width of ~11".

With an ICF wall, you would generally set anchor bolts ever 2', 3', 4' or so in the top of the concrete wall, then attach a treated 2x top plate either the total width of the ICF wall including foam or at least the width of the concrete core.  To directly attach a SIP panel roof, you would likely cut some wedges/shims to match the roof slope and screw those to each side of top plate.  Then use the same long screws that you use for regular SIP panels to screw through the SIP roof panel into the treated 2x top plate that is anchored to the concrete.  That connection should be at least as strong as a SIP roof to SIP wall connection.
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11 Feb 2011 12:57 PM
The following link provides a pretty balanced discussion of the effects of thermal mass in walls:

http://www.buildinggreen.com/auth/a...Issue/


The following is a couple of paragraphs from that link:

"...in many parts of the country, the driving force for conductive heat flow (remember, heat always moves from warmer to colder) can change dramatically or even reverse during the course of a day. On a summer afternoon in Albuquerque, New Mexico, for example, it might be 90°F (32°C) outside, and the outside wall surface—because it has a dark stucco—might be even hotter. It’s cooler inside, so heat conducts from the outside surface of the wall inward. As night falls, however, it cools down outside. The air temperature may drop to 50°F (10°C). The driving force for heat flow changes. As the temperature difference across the wall is reversed, the heat flow is also reversed—drawing heat back towards the outside of the building. As a result of this modulating heat flow through a high-heat-capacity material, less heat from outside the building makes its way inside. Under these conditions, the wall has an effective thermal performance that is higher than the steady-state R-value listed in books (such as ASHRAE’s Handbook of Fundamentals). This dynamic process is what some people call the “mass effect.”

Another common scenario is when the outside temperature fluctuates but never crosses the indoor setpoint temperature. In this case, the direction of heat flow never changes, but the thermal lag or time delay in heat flow can still be beneficial by delaying the peak heating or cooling load. For example, if the outdoor temperature in Miami peaks at 95°F (35°C) at 5:00 on a summer afternoon, but it takes eight hours for the heat to travel through the wall, the effect of that peak temperature won’t be felt inside the building until the middle of the night. Because most cooling equipment operates at higher efficiency if the outdoor air temperature is lower and because nighttime thermostat settings may be higher (at least in commercial buildings), potentially significant savings can result. Not only can total cooling energy be reduced, but peak loads can also be reduced. This can lead to smaller (and less costly) mechanical systems and lower demand charges for electricity. This time lag effect can save energy and money, but note that it does not affect the total amount of heat flowing through the wall."


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11 Feb 2011 01:35 PM
Per the attached temperature graph, Lubbock, TX looks like a good place to take advantage of the thermal mass that a concrete wall offers.

It looks like daily average temperature swings are approximately 25F to 30F from high to low.  From April through October, the daily average high and low temperature swings above and below a typical indoor temperature setpoint.  This is where the thermal mass in an ICF wall provides the most benefit.

http://www.rssweather.com/climate/Texas/Lubbock/

If you went with ICF walls, your heating and cooling system could likely be downsized significantly compared to conventional construction.  Don't make the mistake of oversizing your HVAC system or you would likely miss out on one of the major benefits of ICF. 

If you go with ICF, consider using the following software for HVAC sizing of concrete homes.  This program takes into consideration your location and the mass effect that concrete walls provide.   Most methods for HVAC sizing do not do this and would likely result in a larger HVAC system than needed which would result in higher upfront costs and more equipment cycling and lower comfort levels.

http://www.cement.org/bookstore/pro...emid=cd044

 
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12 Feb 2011 09:39 PM
Steve from Grand County:

That concrete in the walls is anchored in the soil, which in Lubbock, Texas is probably fairly close to the temperature he wants his interior to be.  When that concrete heats up in the Summer, it will conduct heat towards both the soil and the interior.  The path to the interior will have some resistance, the path towards the ground may have a lot less.  In that case, the ground could bleed off enough heat that heat transfer to the interior is greatly reduced compared to what it might be in a cold climate where the soil temperatures are much colder, where people tend to insulate the concrete from the ground also.

One day, I will invest the time to calculate the actual heat transfer rates and figure out an optimal wall for my climate, which is the Alabama Gulf Coast, very hot and humid, but with a soil temperature 4 feet down that is between, I think, 64 and 78 year round, and I think 68 to 72 at ten feet.  Obviously, there is an optimal ratio of thickness of outer insulation, thickness of concrete, and thickness of inner insulation which would make it possible to have no net conduction from outside to inside under average conditions, i.e, passive geothermal. 

Obviously, up North where the soil temperature is very cold (by our standards) that design would never work.

Just a thought, but it would explain why ICF seems to outperform in cooling dominated climates and underperform in heating dominated climates based on the purely empirical results of reading these boards.
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14 Feb 2011 07:43 PM
I'll keep everybody informed on the decision. Concrete is selling right now for about $125 a yard so that may play a factor.

I really appreciate the discussion so far, please continue......
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19 Feb 2011 06:58 PM
As I stated in a previous post, I think using SIP’s or ICF’s to their best advantage depends a lot on the situation. For instance, if you are living in a climate that is very warm during the day and very cool at night, say 90’s during the day and 40’s at night, a solid 8” concrete walled home might be the way to go. The average temperature would be around 70. The concrete absorbing and giving off heat would keep the interior of the home a fairly constant temperature during the daily fluctuations. I think ICF’s, with the insulation provided by the foam would help smooth out these transitions and be very economical. This all works very well because of the “averaging” effect of the concrete.

But, when the outside average temperature drops to the 30’s, and the home inside temperature is 70, the concrete center of the ICF would equalize somewhere around 50 degrees, and you would have an X amount of insulation, depending in the thickness of the EPS foam, between the concrete and the inside wall. If most ICF manufacturers use a 2 ½” wall of EPS foam between the concrete and the inside wall, that’s an R-value of about 4.2 per inch resulting in an R-value of 10.5. Of course, we’re only talking about a 20 degree differential. On the other hand, if your climate is predominantly cold (last week it went down to 45 below), like here in the Rockies, I think you want as much insulation between the inside and outside as possible. Many buildings at the South Pole are built with 12” thick SIP’s.

So, if money is no object, and if it costs more to cool than heat, go with the ICF’s. If it costs more to heat than cool, SIP’s might be the better way to go, all things being equal. The caveat here is that with the concrete, the ICF’s are quite a bit more expensive than SIP’s. Also, the assembly time is longer for ICF’s, and then add to that time to pour. Other problems are lost vibrators, voids, blowouts and thick walls. And if the window or door framing shifts out of plumb during the pour, it can be a challenge to repair. Another minor detail is that it is relatively simple to add a door or window with SIP’s, and somewhat more difficult with ICF’s. I’m not opposed to ICF’s at all. But when it comes to bang for the buck, fast assembly, ease to modify, ease to work with, great insulation values, SIP’s have the upper hand. If there’s a compelling reason to go with ICF’s (fire safety, tornadoes, warm climate, noise issues, hurricanes), sign the check and don’t look back.

Steve
GrandCountySIPs.com
Steve Etten
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19 Feb 2011 09:43 PM
I know the ICF system is said to be more efficient because of thermal mass but the location of the foam versus concrete seems less than ideal. I think in terms of using thermal mass you are much better off using the slab/foundation as your thermal mass. You can isolate (or couple) it with the soil as needed by using foam board insulation. Bill Chaleff has an interesting article on his website regarding using the slab for thermal mass and running ductwork through it to augment cooling/heating. http://www.chaleffandrogers.com/templates/sip2-air_floor_construction.html
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