holly crap, i get busy for a few days and the thread blows up! great info, great read. really gives me what i have been looking for. (obviously this is gone well beyond my original questions and not just directed towards my uses)

"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)"

so how do i eliminate these issues in alaska? i really like adding foam to the outside of the house but i am very concerned about the condensation/molding issue up here? suggestions?

keep it coming. great stuff, thanks agian.

pv

(although a little behind when i get a chance to really evaluate my 100k bid to build the entire house out of icf i'll post up the breakdown)

FBBP,

I'll comment and wish I could find an article that I read comparing a few different load calculation software products.   The article indicated that one of Wrightsoft's cons was that it over sized equipment by almost double for ICF type construction.  Also, many ICF manufactures in the beginning would spin the R value figure by saying that ICF's performed "like" a R50 house.  I gather they meant that a normal leaky build house with R50 bats in the walls is what they were comparing ICF construction.  While you'll still find the R50 reference in some ICF articles, most manufactures are now stating the true R value of their products.  Since ICF has much less air infiltration and the major software product typically oversizes for ICF construction, your load loss worked out being more accurate for the actual load.  

You may be lucky as one poster said.  However, I'd prefer to look at it as you picked the right person to do the load calculation.

Posted By arkie6 on 16 Feb 2011 11:44 PM

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?

just gives me a slightly thicker wall for more insulation. (7.25" with a structural stud every 12", overwall wall thickness plus exterior XPS, or maybe just the ZIP and no XPS). I have also considered 2x6 plates, but at that time you way as well just go with 2x6 studs too.

Lee Dodge,  Thank you for finding my (at least two) typos.   I did intend to use a framing factor of 20 and I did intend to use a 2x6" thickness of 5.5".  

FBBP-- we could spend another 10 pages on this R50 thing.  Here are a few things to consider. 
   
   -- It's been my experience that your typical AC guy can ONLY oventon an ICF home.   In fact, this is the only somewhat serious problem i've ever had in this industry.  A guy that can afford it insists on more tonnage because he can afford it and that's always bad.  Short cycle, doesn't reach dehumid cycle etc.

   -- Today's AC tonnage programs are usually written by the company selling the equipment.   In there defense they do have to stand behind it.  You might experient with this a bit.  If you type in huge R-values you can't escape - you must still buy tons!  :)   I've done some minor tests here and these programs are generally (at least in my experience) based on your typical good old leaky 2x4 house.   Around here 450-550 square feet per ton is typical for conventional tonnage and we usually see 1000-1200 square feet per ton with ICF with a foamed attic (e.g. Richard Rue Analysis).   Off topic here but I believe ICF without a sealed attic is like a screen door on a submarine -- not a good idea.   Now that there's a lot of spray foam in walls you are seeing some move toward the middle like 600-700 square feet per ton for these built better than conventional houses.  Again, off topic here but this tonnage bit is very important to justifying the synergies of various technologies.  E.g. solar does not make sense without geo.  Geo does not make sence without ICF.  ICF does not make sence without a proper attice.  Windows. etc. etc.

  --  Todays AC machines are smarter.  E.g. multi-stage etc. so you can way overton a house and get away with it.  Say put in 10 when it really only needs 5 or 7 and it won't hurt you because the system will simply never run in stage two or three it will remain in stage one.   This is a bit like the 454 engine when you really don't need it and it costs more and it's heavy.  

  -- Regarding R50.  You are right that the basic assuption behind this is that you would have to build conventionally to about R50 to get the same performance as ICF.  I have read this lab report and that's basically the argument.   Although, I don't make these claims I do believe the report is somewhat accurate in intent.  If you've read this long $%$ thread then you know I'm arguring a bit on the other side.  E.g. that ICF is quite accurate and it's everyone else that higher than they really should be.  E.g. typical builder claims r-value of cavity and that's just not true.  The problem with the report is that it attempts (as many do) to roll thermal mass and air infiltration etc. into R-value and well we don't have time to go there.   Sure any air infiltration and you have R-0 but you really can't accurately somehow build lack of air infiltration back into the R-value which was built on and established in the lab in steady state with zero air infiltration.   If air infiltration had anything to do with it many insulations would only be used as AC filters and not put in a wall or roof.

BTW -- putting the definition of R-value aside --- all of this goes out the window with air infiltration.  So any little chaulking misses and you have a drastic reduction in thermal performance (R value number are based on steady state lab calcs).   Then you have the "time" factor (say five years?) and you have expert chaulking and straight lumber degrading to twisted and less than adequate chaulking and we know what happens next -- air infiltration.  Air infiltration makes an R-50 perform like an R-nothing. 

Regards and I apologize in advance for typos :)

 

Posted By pura vida on 17 Feb 2011 02:15 AM
holly crap, i get busy for a few days and the thread blows up! great info, great read. really gives me what i have been looking for. (obviously this is gone well beyond my original questions and not just directed towards my uses)

"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)"

so how do i eliminate these issues in alaska? i really like adding foam to the outside of the house but i am very concerned about the condensation/molding issue up here? suggestions?

keep it coming. great stuff, thanks agian.

pv

(although a little behind when i get a chance to really evaluate my 100k bid to build the entire house out of icf i'll post up the breakdown)

This is off-topic for the ICF forum but OK...

The crude but effective model for calculating it for any climate is to dig up historical weather data for your exact (or very near) location, then design the R-value ratio between exterior foam and framing-cavity foam such that at the mean January temperature (the binned-hourly average, not the average high or low temperature) at the interior face of the foam is 37F-40F or above.  AK is a huge place, with a wide range of climates (Juneau isn't much like Fairbanks or Nome, and Unalaska is considerably warmer than Anchorage.  The very local climate is key to getting it right.)  With the stackup done that way, the interior can be kept at 68F-70F and a comfortable healthy 30% relative humidity without much mold risk, using only modest vapor retarders and "reasonable" air sealing of the interior.  Eg, if the mean January temp for your location is -4F, making 50% of the R value as exterior foam keeps the mean temp at the center-cavity sheathing is 37F or above, and you don't need anything more vapor retardent than standard latex paint, or at most vapor-retardent paint on the interior.  At the stud edges the temps will be warmer still, due to the thermal short to the interior.

If the place has a strong interior side vapor barrier such as polyethylene sheeting or foil-faced batting in the cavities, any exterior foam has to be at least somewhat vapor permeable to allow the framing & sheathing to dry toward the exterior, which places a limit on how much foam you can add.  Going very high-R with foam ends up being too vapor retardent.  But that doesn't mean you can't add some.  The facers on rigid so are vapor retardent enough to demand a stackup that dries toward the interior, and poly sheeting would block that path- can't use it. Unfaced EPS has the most favorable R/perm ratio than other rigid foams- you can put up to 4" of Type-I or Type-II EPS on the exterior (which will be R20+ when its -50F outside, ~R17-18 a @ 0F assuming the studwall has ~R20 cavity insulation.) Building it with a vented rainscreen gap between the siding and foam you can probably bump that to 5".  You can also put up to 5-6" of 2lb Icynene MD-R-200 on the exterior (~ R25-R30 at more moderate winter temps- not sure what it's like in a more cryogenic part of AK), whereas you'd be limited to ~2" (R12-13) with most closed cell polyurethane foams, (or R10 XPS rigid-board.)

Putting ANY exterior R value that's permeable enough to allow the assembly to dry is protective of the structural wood, since it raises it's average winter temp, giving it a higher average vapor-pressure for more drying hours, fewer condensing hours relative to 68-70F.  If you can get it to where it's mean temp in January is above 40F at the sheathing you can skip the interior vapor retarder entirely, unless you're maintaining unusually high interior humidity levels.  (30% @ 68-70F  is reasonable for health & comfort, but some situations call for higher temps & humidity, such as elderly housing, etc. Over 40% RH is never necessary, and over 50% RH is actively recommended against by health professionals for any time of year due to dust-mite & rising mold sport counts.)

In an ICF structure most of the mold-food in construction materials is already completely inside the insulation, and guaranteed to be above the dew point of the inteior air unless you're keeping it truly tropical in there (which is another plus for ICF when built right.)  If you keep the interior RH low enough that the RH at the coldest susceptible material stays below 60%RH you'll be pretty much mold-free.  (Consult the psychrometric chart to figure out where the danger temps are.)  To limit ground moisture from raising the humidity from the inside out, use capillary breaks between the walls and footing, and between the walls and slab (unless you make the vapor barrier under the slab continuous with the capillary break between the footing & wall.  Also use capillary breaks between any concrete & wood contact areas such as foundation sills or joists/trusses, etc.  10mil poly, metal flashing, etc are reasonable materials to use for these purposes, but in some instances you may want to use 1"+ of XPS rigid-board for a combined thermal & capillary break.

Dana: any thoughts on the comments relating to movement and joint separations/failure in stacked up systems like you are always recommending? (thus increasing infiltration down the road)

Texas - My house was not scaled for AC as it is not needed more than 5 days of the year in even a conventional house here in the Calgary region. The only reason we use R values is to determine how much heat (or cool) we will need to supply to the house to make it comfortable with regard to all climatic matters. Based on my observations the gentleman was right to assign a R value of 50 to the ICF. Therefore in my climate to compare the cost of ICF to a stacked up wall, you would have to compare to a wall of R50 (as you said) However the stacked up wall's R value is taken from the same data that says ICF is only R20 something. Do we than have faith that the stack up will actually measure up to R50 in all climates? Also part of this thread is about ICF in cold climate not making sense! It is apparent to me that from the heating portion of the equation it makes dollars. I believe one of the questions on this thread was would the mass stay too cold to make sense during the shoulder seasons or summer. One - since the heating season is by far the most important (from cost point of view) it should be a no brainer. Two - If the temperature rises rapidly so that the external temps are above the house mass, I would open windows and welcome that heat in. That said there will be a lag time between the air temp and the mass temp which 95% of the time is a good thing. Even though many people that deal with ICF in this region will agree that the products are R20ish they will follow that by saying "but they perform much better than that." An they obviously do. So tell me, in the data reports that you folks have been using, how do they obtain the values? Do they vary the ambient temperature from Minus 40 to plus 90? Is that what is making the difference? We know that some materials produce better results at colder climes, does the ICF sandwich do the same? You are probably right that a lot of the other products are over rate but in the end it would not matter as long as it is all relevant to each other. Once again thanks for bringing all the data to the discussion. Bob

Posted By lzerarc on 17 Feb 2011 11:56 AM
Dana: any thoughts on the comments relating to movement and joint separations/failure in stacked up systems like you are always recommending? (thus increasing infiltration down the road)

Studwalls built with air-tight methods are essentially glued together.  Using higher-density fiber or spray foam for cavity insulation, it becomes a secondary air-retarder. (Many builders erroneously assume that a foamed cavity makes the wall an air-barrier, but it is not)  Taped & mastic-sealed rigid foam done as a double-layer with lapping seams, with spray-foam sealed edges are also pretty good over quite a bit of flex range, as are housewrap installations that have detailed as air barriers. 

With the foundation right so that it doesn't frost-heave or settle, and design against racking forces sufficiently it's not as if a stick built house that tests out at 1ACH/50 on day 1 will creep up to 3ACH/30 in 50 years due to separation issues. With air-retardency and air-barrier redundancy built in, it'll fare pretty well unless other things have gone awry.  The most likely increase in infiltration over decades would be from deterioration of windows & doors, something to which ICF construction is not immune.

To be sure ICF done right has some air-tightness advantages, but as I've stated previously, air tightness isn't guaranteed just because it's ICF but it's easier, with less detailing to attend to.  I'm not sure what a "typical" number would be, but without detailing for air barriers during construction, infiltration in excess of 3ACH/50 or even 5ACH/50 on day 1 wouldn't be a shocker by any means.

We have had discussions with the Air Barrier Association of America with regard to ICF at the request of some architects on commercial projects.

Their conclusion is that they recommend an air barrier for any ICF with polypropylene ties since the EPS breathes, concrete does not adhere to the polypropylene and an air infiltration path occurs along the tie system. ICFs with exposed polypropylene studs always require an additional air barrier since there will invariably be some amount of air infiltration along those ties.

ICFs with metal ties and no exposed stud or fastening strip do not require an additional air barrier, because the concrete adheres to the metal cross ties and the concrete then becomes the air barrier. Obviously, you have to pay attention to door and window openings, service penetrations and roof systems, but there are specs for that.

Posted By FBBP on 17 Feb 2011 01:52 PM
Texas - My house was not scaled for AC as it is not needed more than 5 days of the year in even a conventional house here in the Calgary region. The only reason we use R values is to determine how much heat (or cool) we will need to supply to the house to make it comfortable with regard to all climatic matters. Based on my observations the gentleman was right to assign a R value of 50 to the ICF. Therefore in my climate to compare the cost of ICF to a stacked up wall, you would have to compare to a wall of R50 (as you said) However the stacked up wall's R value is taken from the same data that says ICF is only R20 something. Do we than have faith that the stack up will actually measure up to R50 in all climates? Also part of this thread is about ICF in cold climate not making sense! It is apparent to me that from the heating portion of the equation it makes dollars. I believe one of the questions on this thread was would the mass stay too cold to make sense during the shoulder seasons or summer. One - since the heating season is by far the most important (from cost point of view) it should be a no brainer. Two - If the temperature rises rapidly so that the external temps are above the house mass, I would open windows and welcome that heat in. That said there will be a lag time between the air temp and the mass temp which 95% of the time is a good thing. Even though many people that deal with ICF in this region will agree that the products are R20ish they will follow that by saying "but they perform much better than that." An they obviously do. So tell me, in the data reports that you folks have been using, how do they obtain the values? Do they vary the ambient temperature from Minus 40 to plus 90? Is that what is making the difference? We know that some materials produce better results at colder climes, does the ICF sandwich do the same? You are probably right that a lot of the other products are over rate but in the end it would not matter as long as it is all relevant to each other. Once again thanks for bringing all the data to the discussion. Bob

Do tell!

Data?

What stackup/building did you compare it against?

Was the air infiltration measured on each?

Glazed area & type can easily equal or exceed all wall-area heat loss once you're in the R20 clear-wall range- was that controlled in your comparative study?

Was the roof insulation & roofing type identical/comparable?

Did you actually measure ANY stick built with an actual R50 wall (of which there are damned few in Alberta but some... there is probably at least one in Calgary) by which you're making the comparison?

If you're comparing low density R20 batts in a leaky 2x6 16" o.c. stick-built with no exterior foam, it's not really the right test. (Nobody is building that way in my neighborhood these days, not that the average or typical is all that great. I've seen existence proofs that advanced framing and 2x6 out-sulation with air sealing can work, and work well, just as I've seen ICF buildings that work well.

While diurnal swing in Calgary are high enough to use the thermal mass in an R20 ICF, it's still less than a 10% deal if all else is equal.  (And that includes everything from glazing & insolation, air infiltration rates, roofing type & color.)  Just because the standard for stick-built from 25-50 years ago (or even 15years ago) were pretty abyssmal, that doesn't mean the approach is guaranteed to fail, or that ICF will always succeed. 

I suspect your test cases by which you're making this assertion has more to do with air-leakage rates than R-value and certainly not the effect of the thermal mass.  The Oak Ridge National Labs guys aren't hacks with an agenda to sell sub-standard methods- I accept their assessments, since they actually measure stuff in a controlled fashion.  The large scale climate simulator has been around for about a couple of decades now, and has been used to test assemblies in temperature & humidity ranges well in excess of what you'd actually see in Calgary.  According to their analyses & data, the best improvement you'd see going with an R20ICF vs. a stick-framed stackup with an R20 whole-wall R would be on the order of 9%, in cooling dominated climates:  http://www.ornl.gov/sci/roofs+walls...igure8.pdf  (note that in Minneapolis, which is closest to a Calgary climate, you're talking a 6% difference.)  Note also that all curves are assymtotic to some level between 5-10% with increasing R, independent of climate zone.  Were the mass completely inside the thermal boundary it would continue to creep up with higher R (which is well modeled by other simulations for other purposes.)  The interior foam isolating the conditioned space from the mass limits the mass benefit, which is another reason why most or all of the concrete in most PassiveHouse designs are inside the insulation.

The only case in which an R20 ICF might perform anywhere near an R50 comparison would be an ultra low-mass house is in strongly cooling dominated climates with large diurnal temperature swings, with the bulk of the insulation of the ICF on the exterior:  http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/figures/figure7.pdf  That  performance difference wouldn't be the case if the low mass R50 house had a slab foundation or were earth-coupled in any fashion.

The EPS in an ICF does increase in R-value at the low-temp extremes. At -40 the outer EPS of an R20 ICF would be running R12-R13, but the inner would still be in the R10-11 range.  At the high end of your temperature extremes (90F, not C, I presume? :-)  ) the outer foam is performing to about R8 only, but the thermal mass is boosting performance. (It's never 90F at night in Calgary- the dry air allows it to drop quickly after sundown, unlike in swampy sticky FL or coastal TX.)

Guys, girls, and especially ICF folks-

How are some of you guys designing houses?  I hear these crazy comments about "I have ICF walls rated at R-22, but they behave like R-50 compared to a stick house."  R values are not some kind of relative number based on a stick house.  They are an absolute numbers for thermal resistance, and are the inverse of conductance expressed as Btu/(h-ft^2-degF) in American units.  They work as well for ICF houses as for stick, SIPs, and every other house.  How can you make decisions about what components and insulation levels to put in your house without doing the calculations?  How is your actual energy used comparing with your design calculations for different R-values?  That information would allow us to say that, "yes, this ICF house is performing better than is predicted by the R-values and measured infiltration factors based on blower door tests."  Otherwise, your information just consists of some random opinions, and comparisons with outdated stick house designs.

I wanted to build an ICF house last year, but ICF's are expensive in this area, and we don't have earthquakes or fires or much else I could use to justify the extra cost.  Actually, I still might have spent the money, but I was concerned about the lack of experience by the builder and subs.  But I certainly did some modeling to compare the various options.  These models were pretty much all free models.  You can use REScheck (free) to compute the U*A (conductivity * area) for the house, and then multiply that by degree days converted to hours to get conductive heat losses for the whole house.  Take blower door data at 50 Pa, divide by 20 to approximate natural infiltration, multiply by degree days converted to hours, and you have an estimate of infiltration energy.  (Or study Max Sherman's work, and put some additional fudge factors in this calculation to improve it.)  If you use mechanical ventilation, then add that into the infiltration number.  Use RESFEN or HEED (both free) to compute passive solar gain.  Use PVWatts 1.0 or 2.0 if you have solar PV to estimate electrical generation.  It seems to me like you need this information to make educated decisions about how to design the house.  (I will try to put more details for this approach on my website, buy have not yet done it, but hopefully these procedures are fairly transparent.)

I did these calculations before we began construction on my stick house, as shown below.  Some numbers are more guesswork and based on historical usage than models (e.g., solar thermal), but you still need to have some idea of predicted energy usage if you want a net-zero or low-energy house.  Some numbers I have adjusted based on measurements as time has evolved, like the solar PV output.  The actual numbers are not so important (and I don't want to defend them here - see website for details), but I include them to indicate that I have done my homework: 

                              annual MMBtu
H_conduction                     28.1
H_infil+mech vent               13.0
H_heat_recovery_vent        -2.2 
H_domestic_hot_water      10.6
E_elec_appl_heat_loss         -6
H_passive_solar                  -12.9
H_solar_thermal                  -6.9
E_excess_solar_PV            -9.4
E_net*                               -5.6
* including source energy terms (http://www.energystar.gov/ia/busine...source.pdf)

I am currently putting my gas and electrical utility usages and bills on my website for all to evaluate, not colored (too much ) by my opinions.  My energy use seems to be following the model results fairly well, except the PV system is ahead of the original predictions, so I adjusted those numbers.  After a full year and more careful comparisons, I will be in a position to comment on the accuracy of the R-values, etc. 

I think this approach will provide a firmer basis for seeing if the R-values for a house appear to represent actual performance.  I look forward to seeing these numbers for ICF houses (with R set to 22 and 50), SIPs, and other stick houses. 

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

HVAC Sizing Methodology for Insulated Concrete Homes:

http://www.toolbase.org/Design-Cons...ethodology

Click on the embedded pdf link for details.

"HVAC Sizing for Concrete Homes" software can be found here:

http://www.cement.org/bookstore/pro...emid=CD044

Whoa there Dana!!! Please reread my post. I am simple asking questions to determine why my house is performing much better than the data you and the other gentlemen have been using to debate the use of ICF's in cold climate and the comparison to stick built stack wall. I did not say I had done any comparison. I simple followed up on what Texas had said about using R values to compare. If we are going to compare ICF in Calgary like climes, we should compare to the equivalent stack up of R50. I did question the data used for the stackup as it would appear that the results for ICF are not correct. If whatever changed the value of the ICF also changes the value of the stack, it would make things look quite different. I did not call into question any of the experts that produced the data that you used. I honestly want to know if the test were done in different ambient temperatures. A simple yes would suffice. I am not modelling my house. I am not theorizing. I simple gave the area of my house and what it was taking to heat it. It would seem to me that heating a house with resistance is a fairly good way to test modelling performance. If the only input to the house (it is not being lived in as yet) is two 3000 watt elements, it would seem to be easy to measure. If you convert the watts to btu and compare it to the area of the house or if you would like to reverse model it, I think the conclusion is that with this amount of wall area, the ICF simple has to be performing well above R20. It does not matter what windows I have as they only drag the walls performance down. (The are top of the line triple glaze low e argon filled) Even if you model the house with R60 ceiling (and its close) and you allow for zero infiltration I believe the model would show that the ICF has to be performing better than R20. The whole purpose of this thread was to compare ICF to stick built. The facts that I have from my house would indicate that the comparisons were not accurately reflecting what I see here. Hence my input. You continue that assertion by say the best I can hope for is 9%. If anyone out there has a 2x6 stick built house, however built, that only needs 9 % more than these inputs, I would be very excited to hear from you.

FBBP, Quite a mystery isn't it. There is no question (myself included) that if you live in an ICF house there's no going back. My heating and cooling is 20% of my neighbors and I can prove it because I took Richard Rue's advice and had my geo separately metered. Do the words McMansion mean anything to you. This is like being gifted an F-16 -- sure it's worth say 20 million but where are you going to come up with the 2 million a year you need to maintain it.

A few years ago it was not uncommon (and it still happens) for someone to build as big as they can afford (or get a loan) -- not really the best approach.

What bothers me most about all this is the guy with a 10K square foot house may or may not care if he pays $1000 per month to heat and cool it. It's the guy with the 1500 square foot house with the $250 per month bill that really needs the ICF. Regards.

well, even though the thread may be a little past it at this point (which is fine) here is breakdown i received for building my entire house out of icf:

using ARXX blocks

material:
     16-3/4 X 48 standard blocks     950    $23/block
     16-3/4 X 48 corner blocks         96      $23/block
      8" loc block                             2200    $1.3/block

hooks, zip ties, foam, screws, bracing  remaining cost

total $31,500



install:

house footings and basement wall
   185' of wall
   250' of footings
   84 yards of concrete, 8 hours of pump truck, etc

$25,000

Main floor and garage wall
    363' wall
     151 yards of concrete, 11 hours pump truck, etc

$31,600

Garage foundation
    178' of footings and stems
     40 yards concrete, 4 hours pump truck, etc

$10,500




so there it is for what its worth.  right now i am thinking i'll do the basement out of icf but probably not the rest of the house.  leaning towards double stud wall with possibly some foam board (eps).

pv

so even though not really icf related, as stated above, i'm leaning towards doing an icf basement and a double wall for the main floor and garage. 1 to 2" of eps on the outside, 2X4s for the outside wall 2X3 inside walls. is it possible to put the vapor barrier on the outside of the inside wall to avoid electrical and plumbing breaks? the point being able to maintain a more constant vapor barrier throughout the house. would this help with the mold issue? or am i missing something? what about putting the foam on the inside wall?

pv

Posted By TexasICF on 17 Feb 2011 09:23 PM
FBBP, Quite a mystery isn't it. There is no question (myself included) that if you live in an ICF house there's no going back. My heating and cooling is 20% of my neighbors and I can prove it because I took Richard Rue's advice and had my geo separately metered. Do the words McMansion mean anything to you. This is like being gifted an F-16 -- sure it's worth say 20 million but where are you going to come up with the 2 million a year you need to maintain it.

A few years ago it was not uncommon (and it still happens) for someone to build as big as they can afford (or get a loan) -- not really the best approach.

What bothers me most about all this is the guy with a 10K square foot house may or may not care if he pays $1000 per month to heat and cool it. It's the guy with the 1500 square foot house with the $250 per month bill that really needs the ICF. Regards.

Texas - I read you loud and clear. The other part of the equation is that many time people figure they can't afford the ICF but if they take their mortgage payment and their heating bill together their total monthly payment up here is normally less with ICF. Also you can eventually pay off the mortgage but you will never get rid of the fuel supplier. About the guy who doesn't care about his heat bill, do you have any idea of how much natural gas is burnt up here for snow melt? I can't wait for n. gas prices to double. Course most of these guys are in oil and gas so they probably still won't mind. Bob

Posted By pura vida on 18 Feb 2011 12:30 AM
so even though not really icf related, as stated above, i'm leaning towards doing an icf basement and a double wall for the main floor and garage. 1 to 2" of eps on the outside, 2X4s for the outside wall 2X3 inside walls. is it possible to put the vapor barrier on the outside of the inside wall to avoid electrical and plumbing breaks? the point being able to maintain a more constant vapor barrier throughout the house. would this help with the mold issue? or am i missing something? what about putting the foam on the inside wall?

pv

pv - it is certainly possible and will give you a better v. b. but you should reread Dana's comments on the moisture situation. Depending on how you install the eps and what "filler" you use in the space, you might be better off with no v.b. Dana has given some pretty in depth discuss about dew point and breathablity of walls

Thanks arkie - the literature does shed some insight into the issue. Especially "Thermal resistance (R-values) and thermal transmittance (U-factors) do not take into account the effects of thermal mass, and by themselves, are inadequate in describing the heat transfer properties of construction assemblies with significant amounts of thermal mass (VanGeem, 1987)." It is clear from the literature that we can not say "ICF's have and R value of" It is also clear that the mass will out perform low mass buildings under certain conditions. In some ways it makes it harder to compare building methods for cost and efficiency but it would be fun to run my house to see if it matches the actual performance.

Pura Vida, that looks like about $17.72 per square foot including footings. Do you have poured floors as well? Any chance you could reverse out the footings and horizontal concrete so we can see what the total cost was for walls alone?