I was going to reply to the "Wall Cavity Insulation" thread but decided to start a new one instead of hijack.  So..

Dana -

You are obviously extremely knowledgeable about wall stackups, moisture infiltration, etc.  I see different methods & materials thrown around on these boards and you always seem to provide a great pro/con of each.  So my question is, how would you build a house?  I'm not so much interested in a "money no object" scenario, but a realistic one.  Looking at insulation, air sealing, passive solar, active solar, heating systems, the whole nine yards - how would you put together an extremely energy efficient, healthy house that doesn't break the bank?


thanks!

Very good question, I look forward to hearing the responses!  I myself keep bouncing between urethane SIPs (including basement SIPs), double stud and cellulose, single stud and ext. XPS, and ICF (full pour from basement to roof, floor structure suspended), and combination of all of the above.

You would probably want to have the answers specific to a few various climate profiles. Minnesota, Texas, FL etc....

I'd build a tight 8" walled earth-coupled concrete house on a sunny island at about 25 degrees north latitude, on a warm ocean current, with maybe R10 of EPS on the exterior. (Hammocks & palms optional.) ;-)

How you build depends a lot on what your heating & cooling requirements are, and the local climate. SIPs are great if you have a lot of time to really work the plan, and have an installer up to snuff, but it can be an expensive way to go high-R.

Stick-built with 2x6" 24" o.c. with advanced framing technique to limit thermal bridging and insulation voids is pretty straightforward, with the total R adjusted by the thickness of the exterior foam. It's fairly flexible and easy to build up to ~ R40 clear wall values (using 3.25" rigid iso on the exterior.) Building the foundation with assymetric ICFs (fat-side toward the exterior) with the exterior face of the forms aligned with the plane of the sheathing foam works to limit thermal bridging at the rim joist & sill too. Some builders insert an exterior step in the concrete to allow the sheathing foam to extend below the rim joist, but the added complexity may not be worth a marginal performance gain if the ICF's exterior foam at least half the R of the sheathing's foam at the temperatures you care about. For cavity insulation, wet-spray cellulose is usually the best installed-R/$ value, and adds a bit of thermal mass to the system, as well as some hygric buffering. (But the value of that buffering is somewhat reduced if there is sufficient exterior foam such that the sheathing is literally NEVER below the dew point of the interior air.

Making multiple air sealing passes at different phases of construction is about the cheapest total-enhancement you can make. A well insulated wind-tunnel of a house is a problem, and retrofitting it to air-tightness is more expensive/less-reliable than building the air-tightness at the get-go.

Its worth running the crunch with modeling tools such as the PassiveHouse, DOE2, etc to figure out where the tradeoffs are for R-value, glazing type & size for each side of the building & shading factors & climate etc. An R50 wall doesn't buy you much if it's only 40% of the wall area, no matter how great the windows are. You don't have to live in the dark to get a good overall energy factor on the house, and in heating-dominated places building-in the right balance of passive gain will leave you with pretty signifcant views on the south side, if the shading factors are right. In cooling dominated places the right balance of thermal-mass & solar gain can be HUGE in limiting energy use & maximizing comfort.

I'm partial to the PassiveHouse approach, but in most of the heating-dominated US you'd need a clear wall R greater than R40 to meet their standard, adding complexity & expense to the proposition. But you'd be more than halfway there if you plan the glazing, doors & air-tightness in. In some places it's well-worth insulating under the basement slab (or grade-slab), in others its worth earth-coupling the foundation, but that can all be modeled. There is no one-size-fits all solution- it depends, but modeling those dependencies at the design phase directs you better as to where to spend the money. But with the building envelope well-tuned to the climate, you spend a lot less on mechanical systems to support the much-reduced heating/cooling loads, and you won't need to care as much about their absolute efficiency. The difference between an 80% fossil-burner vs. a 95% efficient one isn't worth spending much money on when the difference in fuel use per year is under 50therms (the showering-time of your kid can make a bigger difference than that! :-) ) When your water heating energy use only as big or bigger than your space heating/cooling energy you know your getting close, making a potential future Net-Zero-Energy retrofit at least possible. What that takes will vary a LOT by climate zone and site-specific factors.

Interesting.  So you favor a 2x6 advanced framing with exterior foam and cellulose over a double stud wall for example?  From the estimating and pricing I have done, the double stud wall (2x4s), roughly 9.5" thick with cellulose, ZIP ext. sheathing still runs cheaper then 2x6 with exterior foam.  Granted, you trade off some floor space possibly.
  It also doesnt sound like (or at least wasnt mentioned) above ground ICF as a favorable option?

Also it seems you like the SIPs panels as well.  I am in the same place.  I have debating between a FULL SIPs (basement included, no roof though), poured or ICF basement with SIPs, or the double stud wall/2x6 with ext. xps.  However the urethane r-24 3.5" SIPs cost about $3000 more for materials then the 2x6/xps option, and the 6" r-38 costs about $5000 more.  I am debating if this is worth it, especially with the time savings.  I would sit the SIPs directly on the foundation, and leave a 2-3" ledge to set my floor trusses on.

It really depends- the labor costs of of double studwalls vary a lot by local market, and the detailing around the thermal bridging issues (both design & implementation) are easier to screw up than a studwall + rigid foam solution. But starting somewhere around R40 & higher, double studwalls (or engineered I-beam studs) become more cost-effective. If you're only counting material costs for high R (as in R35+) double studwall approaches start to look VERY attractive.

ICFs for above-grade can be quite expensive relative to their thermal performance at high-R, but at moderate R in moderate or cooling dominated climates the value-added of the structural aspects of ICF have to be factored in. jerkylips was '...not so much interested in a "money no object" scenario, but a realistic one.' Realistically, an all ICF solution in a heating dominated climate might break the bank, with only a very most modest benefit from the thermal mass. In places where sound-attenuation of outdoor noise is a factor you're willing to pay for you'll do better with ICF. In cooling-dominated US climates it's worth looking at though, particularly going with asymmetric-R variants (higher R on the exterior) to utilize the mass better.

I'm not super-enamored of SIPs either, but if done WELL it can still be quite cost effective at high-R when labor costs of alternative methods are considered. Done poorly they're an expensive inefficient semi-disaster. (I've seen both ends of the spectrum.) They're inherently low in thermal mass, and designing in some internal thermal mass to the building to moderate peak loads may be desirable. It's the other end of the spectrum from ICF for sound attenuation factors- building next to a busy intersection or noisy highway might tip the scale away from SIPs and toward double-studwall (if the required R is high), or ICF (if the required R is low/moderate.)

In many places (such as coastal CA) it's possible to hit PassiveHouse levels of primary energy use with sub-R30 walls and a good design, but you have to DESIGN it, taking into account both site & climate specific aspects. Half the US could get there at R40 or less, or at least down to a level where Net Zero Energy is at least possible. Up to about R40, from a design, stackup, & build-ability point of view advanced framing + exterior foam would be easier to pull off for most.

http://www.buildingscience.com/documents/information-sheets/high-r-value-wall-assemblies/high-r-wall-02-advanced-frame-wall-construction

(from http://www.buildingscience.com/documents/information-sheets/high-r-value-wall-assemblies)

Here Net Zero was achieved here with mere ~R32 walls in a 7000+ heating degree-day climate, but only with high-efficiency geo + 11kw of PV solar- not exactly cheap, but makes the point that Net-Zero can be done with sub-R40 almost anywhere with a foam+ studwall wall stackup. With a PassiveHouse approach in that location they probably would have doubled the walls' R values, skipped the geo, cut the PV by half and still made Net-Zero with electric resistance heating, but R-values that high wouldn't be as simple as a studwall + foam solution with standard framing lumber: http://www1.eere.energy.gov/buildings/challenge/pdfs/high-performance_builder_spotlight_timobrien.pdf

Not enough attention is paid (yet) to foundation & slab insulation- and those heat flows can make or break an otherwise good design. With high-R walls and minimal glazing, interior wall temps even at design-day conditions will be in the high 60s F, and a 55-60F basement slab could well represent the largest average heat load to the building- half the heating bill or more. It's hard to model well, since subsoil temps are sensitive to site conditions (and you're not likely to build monitoring wells to track them through a few seasons prior to building.)

Dana,

 

Thanks for the excellent reply as always.  My question was mostly hypothetical, but not completely.  We just built a house, but may be selling & building another in the not too distant future.  Long story…

 

Based on what I’ve learned through this process, I came up with a rough idea of what I THINK I’d like to do.  Do you see any major flaws with this?

 

House will probably be 1700-1800 sq ft ranch, with another 1000ish in finished basement

 

2x4 construction 16”OC – no advanced framing (my understanding is that doing 2x4 & 24”OC, you must “stack” the load bearing walls – not sure that will work with the floorplan we’d be using)

Dense pack cellulose (R14)

4” XPS foam board outside (R24)

Raised heel trusses

“attic seal’ (we did this in our current house – they basically spray foam all connection points in attic as well as around recessed cans)

R60ish in the attic

9 foot ceilings, probably no vaulted ceilngs (we have 10 foot & a 14 foot vaulted currently – it echos & isn’t very “homey”, plus the heating/cooling issues)

Basement – insulated slab (not sure EPS or XPS…or how much – have heard mixed things on what’s really necessary)

2” XPS around foundation

PEX in slab for radiant

Basement heated with either solar hot water, pellet furnace, or wood gasification boiler (basement probably won’t be used every day, so heated as needed)

A small gas forced air furnace (we also significant cooling needs in the summer, & need ductwork anyway, so I prefer this to radiant for 1^st floor)

HRV

Pre-wired for PV, for when prices come down

High SHGC windows on south side, with overhangs to block summer sun (we did this in our current house, and now that the sun is getting lower in the sky, we’re getting TONS of mid-day heat –  recently it was in the 40’s but sunny, furnace off, & it got up to about 75 inside before we opened the windows to cool it down)

On another note, there are a couple things we didn't do that I wish we would have, & definitely will if we build again (not really "efficiency" related)
electrical outlets in closets - for rechargeable stuff
attic / storage trusses in garage
another service door in the garage (we have one to the backyard, but nothing accessed from driveway/front - builder talked us out of it since we have the keypad for the garage door.  I find it to be ridiculous to open & close the garage door all the time when I want to go outside)

edit - forgot to add that this is in Green Bay, WI - roughly 8000 HDD

Going with 4" of foam on the exterior runs into structural issues for supporting the siding with it hanging so far out from the structural wood. (And 4" of XPS is R20, not R24, BTW.) You can probably make that work with vinyl, but with cement board, not so much (without extra work.) Something like 3" of fiber faced iso (~$55 per 4x8 sheet for 3", f.o.b. the distributor's lot) yields the same R for less money, it's lighter, and the siding has a smaller moment-arm pulling on the fasteners. Using 2 layers with overlapping seams , sealed on both layers, makes for measurably better air tightness, at a slight increase in material cost, but the installation labor cost would go up by a bit (not 2x but at least 1.5x the labor). The air-tightness is still worth it though.

2x4 16" o.c. is more expensive to frame than 2x6" 24" o.c. of similar load capacity. The stud-depth limits cavity insulation depth, and with 50% more studs at R3.5 instead of R5.5, you get more than 50% more thermal bridging, That R14 dense-pack is center-cavity best-case only, at 4lb density. For a more likely 3.2-3.5lb dense pack you'd be looking at a realistic R13 center-cavity, and with the bridging of the studs factored in you're closer to R12 for clear-wall R. With 2x6 & 24" o.c. wet-sprayed (lower density) you'd be at ~R19-20 clear-wall for similar or lower framing & insulation costs. There are ~30% fewer boards to cut for less installation labor using the same number of raw board-feet in the framing timber, and you're looking at only ~2/3 the dry-weight on the cellulose, with about half the installation labor.

As-described your clear-wall total stackup will likely run R32, best-case, R30 likely. With a thicker 2x6 wall of similar load capacity and lower cost you'd be at R36 or more, which reduces the wall's heat loss/gain by ~20% with no cost adder. Windows & doors & infiltration then dominate the heat loss/gain of unless you intentionally minimize the total glazed area, which IS a good thing to model. You don't really NEED huge picture windows for good daylighting and views, and with your heat loads it makes sense to cut back on glazing where you can, and managed it carefully for the solar gains- particularly on the south side. Using some average numbers for fudge-factors the "whole wall" R (windows & doors included) of the 2x4 + XPS solution will run ~ R28-29, while the 2x6 + iso would be ~R34-35.

With ~50% or more of the R outside the structural sheathing and moisture-buffering cellulose in the studs A: The sheathing never dwells at temps below the interior air dew point long enough to matter in your climate and B: you should NOT use anything more vapor-retardent than latex on the interior, siince either 4" XPS and most fiber-faced iso (with facers x 4, 2 per layer) don't give it much drying capacity toward the exterior.

Insulated concrete forms with 3-4" of EPS on the exterior and 2" on the interior would give you an R20-R25-ish foundation wall vs. R10 with your exterior 2" XPS. There are other higher-R options available as well: http://www.quadlock.com/green_building/building_shell_superinsulation.htm (just one vendor of many- there are some fudge-factors added into their assumptions- read the footnotes.) Making the R value of the basement walls at least 1/2 to 2/3 of the clear wall R-value of your first-floor is important, at least down to the frost line (which may be the whole shebang in Green Bay.) With lower glazed area, the average whole-wall U value of the foundation will be similar to that of the above-ground. With your stackup & studwall specs, you'd need to go at least R15 (3" of XPS) on the foundation for it to have a similar average heat loss.

Under the slab 2" of EPS (R8) is probably fine if were semi-conditioned (not actively heated space- no radiant.) But fully conditioned, 3" (R12) is better, and 4" (R16) better yet, especially if your heating it with precious active solar keeping the slab above the temp of the room-air. But skipping the active solar for space heating would be my advice- not enough bang for the buck when you need it most- spending it on higher-R overall and designing the passive gains would be cheaper/better. Active solar has a rationale for DHW, but for a high-R house passive solar works better- design it in (buy some software, or consult with a designer with some experience.) With all high-R houses you really need to manage the solar gains- it's easy to end up with an overheating condition, even during the heating season if you leave it to chance. And with passive solar tempering your heating SEASON is much reduced- you'll be able to cool the place during the shoulder seasons by adjusting the ventilation (such as opening the windows method you discovered. :-) )

If you go thick enough on the exterior ICF foam to have to cantilever the joists out beyond the foundation concrete to get the outer planes of the foundation & sheathing foam aligned, that's not a disaster, just detail, and an easier/stronger detail than having to hang it on the interior edge of the concrete.

Subsoil temps in Green Bay are cool- about 48-50F (see http://mb-soft.com/solar/soilmap.gif ), and as soon as you have R5 under the slab the insulating effect of the slab will exceed that of almost ANY type of soil, dominating the heat flux model, so for R8 or higher you can pretty much treat the heat-flux issue as if it were a constant between a the basement room temp and the subsoil temp, ignoring the thermal mass and insulating factors of the soil itself. (It'll still be a measurable, secondary effect, but not important enough to drive the design.) Would you insulate the exterior walls to only R5 in an climate with an average January outdoor temp of 48F? Methinks not! In Green Bay the mean January temp is ~16F (see: http://www.ncdc.noaa.gov/oa/climate/online/ccd/meantemp.html ) , a ~55F delta-T between room temp & average outdoor temp. The 48F subsoil temp is about a 20-25F delta, or between 1/3 & 1/2. To keep the heat loss per square foot similar to that of the rest of the house during the middle of the heating season, the sub-slab R needs to be at least 1/3-1/2 of the whole-wall (window & door losses included) of the first-floor walls. That heat loss out the slab will be higher than the rest of the house during the shoulder seasons & summer when it's warmer outside, but that's pretty much OK- you've designed in the passive gains to pretty cover the whole-house heat losses during the shoulder seasons, right? Anything less than ~R5 will be a comfort issue for bare feet. If less than ~R2 you have potential condensation/mold issues under wood flooring or rugs during the summers, keeping the basement using 75F, 65% RH for upper bounds.

A small condensing gas furnace makes sense- they're cheap & efficient, and in a high-R house the cush-factor of radiant is nearly non-existent (most of the time the floor would only be a degree or two above room temp, and not particularly warm to the feet) and since you're in a forestry-rich region pellet burners are probably reasonable too. Bear in mind that with high R and reasonable thermal mass with a well-modeled design surrounding the solar gains, the bulk of your cooling load will be dehumidification, not sensible cooling. Whatever AC unit you put in there needs to have an efficient dehumidification mode, which won't necessarily correlate well with a high SEER number.

2X6 ove less work and is the same cost makes more sense Use a simple shape, minimize corners
Use a 8’ wall height but use a scissor truss with an energy heel. This gives some illusion of height but not so high that it kills efficiency. Also allows for the use of ceiling fans which can aid heating and cooling efficiency.
ICF basement walls as insulated as possible, 2-4” xps under the slab
Gas furnaces are good, Pellet stove may not be able to fire low enough to not overheat the house.
Good windows are key. Passive solar can make a huge difference.
Pay close attention to electrical usage. With good insulation and air sealing in the house + passive solar, general electrical usage can cost a lot more than HVAC bills.
Carefully consider solar air heaters, and a solar DHW system.
Build as small as your wife will allow without killing you
With 4” of exterior insulation, you will likely need substantial furring strips to attach siding to.
Dogs are good for about 400 btus/hour
Cheers,
Eric

Posted By Dana1 on 11 Nov 2010 02:29 PM
Going with 4" of foam on the exterior runs into structural issues for supporting the siding with it hanging so far out from the structural wood. (And 4" of XPS is R20, not R24, BTW.) You can probably make that work with vinyl, but with cement board, not so much (without extra work.) Something like 3" of fiber faced iso (~$55 per 4x8 sheet for 3", f.o.b. the distributor's lot) yields the same R for less money, it's lighter, and the siding has a smaller moment-arm pulling on the fasteners. Using 2 layers with overlapping seams , sealed on both layers, makes for measurably better air tightness, at a slight increase in material cost, but the installation labor cost would go up by a bit (not 2x but at least 1.5x the labor). The air-tightness is still worth it though.

2x4 16" o.c. is more expensive to frame than 2x6" 24" o.c. of similar load capacity. The stud-depth limits cavity insulation depth, and with 50% more studs at R3.5 instead of R5.5, you get more than 50% more thermal bridging, That R14 dense-pack is center-cavity best-case only, at 4lb density. For a more likely 3.2-3.5lb dense pack you'd be looking at a realistic R13 center-cavity, and with the bridging of the studs factored in you're closer to R12 for clear-wall R. With 2x6 & 24" o.c. wet-sprayed (lower density) you'd be at ~R19-20 clear-wall for similar or lower framing & insulation costs. There are ~30% fewer boards to cut for less installation labor using the same number of raw board-feet in the framing timber, and you're looking at only ~2/3 the dry-weight on the cellulose, with about half the installation labor.

As-described your clear-wall total stackup will likely run R32, best-case, R30 likely. With a thicker 2x6 wall of similar load capacity and lower cost you'd be at R36 or more, which reduces the wall's heat loss/gain by ~20% with no cost adder. Windows & doors & infiltration then dominate the heat loss/gain of unless you intentionally minimize the total glazed area, which IS a good thing to model. You don't really NEED huge picture windows for good daylighting and views, and with your heat loads it makes sense to cut back on glazing where you can, and managed it carefully for the solar gains- particularly on the south side. Using some average numbers for fudge-factors the "whole wall" R (windows & doors included) of the 2x4 + XPS solution will run ~ R28-29, while the 2x6 + iso would be ~R34-35.

With ~50% or more of the R outside the structural sheathing and moisture-buffering cellulose in the studs A: The sheathing never dwells at temps below the interior air dew point long enough to matter in your climate and B: you should NOT use anything more vapor-retardent than latex on the interior, siince either 4" XPS and most fiber-faced iso (with facers x 4, 2 per layer) don't give it much drying capacity toward the exterior.

Insulated concrete forms with 3-4" of EPS on the exterior and 2" on the interior would give you an R20-R25-ish foundation wall vs. R10 with your exterior 2" XPS. There are other higher-R options available as well: http://www.quadlock.com/green_building/building_shell_superinsulation.htm (just one vendor of many- there are some fudge-factors added into their assumptions- read the footnotes.) Making the R value of the basement walls at least 1/2 to 2/3 of the clear wall R-value of your first-floor is important, at least down to the frost line (which may be the whole shebang in Green Bay.) With lower glazed area, the average whole-wall U value of the foundation will be similar to that of the above-ground. With your stackup & studwall specs, you'd need to go at least R15 (3" of XPS) on the foundation for it to have a similar average heat loss.

Under the slab 2" of EPS (R8) is probably fine if were semi-conditioned (not actively heated space- no radiant.) But fully conditioned, 3" (R12) is better, and 4" (R16) better yet, especially if your heating it with precious active solar keeping the slab above the temp of the room-air. But skipping the active solar for space heating would be my advice- not enough bang for the buck when you need it most- spending it on higher-R overall and designing the passive gains would be cheaper/better. Active solar has a rationale for DHW, but for a high-R house passive solar works better- design it in (buy some software, or consult with a designer with some experience.) With all high-R houses you really need to manage the solar gains- it's easy to end up with an overheating condition, even during the heating season if you leave it to chance. And with passive solar tempering your heating SEASON is much reduced- you'll be able to cool the place during the shoulder seasons by adjusting the ventilation (such as opening the windows method you discovered. :-) )

If you go thick enough on the exterior ICF foam to have to cantilever the joists out beyond the foundation concrete to get the outer planes of the foundation & sheathing foam aligned, that's not a disaster, just detail, and an easier/stronger detail than having to hang it on the interior edge of the concrete.

Subsoil temps in Green Bay are cool- about 48-50F (see http://mb-soft.com/solar/soilmap.gif ), and as soon as you have R5 under the slab the insulating effect of the slab will exceed that of almost ANY type of soil, dominating the heat flux model, so for R8 or higher you can pretty much treat the heat-flux issue as if it were a constant between a the basement room temp and the subsoil temp, ignoring the thermal mass and insulating factors of the soil itself. (It'll still be a measurable, secondary effect, but not important enough to drive the design.) Would you insulate the exterior walls to only R5 in an climate with an average January outdoor temp of 48F? Methinks not! In Green Bay the mean January temp is ~16F (see: http://www.ncdc.noaa.gov/oa/climate/online/ccd/meantemp.html ) , a ~55F delta-T between room temp & average outdoor temp. The 48F subsoil temp is about a 20-25F delta, or between 1/3 & 1/2. To keep the heat loss per square foot similar to that of the rest of the house during the middle of the heating season, the sub-slab R needs to be at least 1/3-1/2 of the whole-wall (window & door losses included) of the first-floor walls. That heat loss out the slab will be higher than the rest of the house during the shoulder seasons & summer when it's warmer outside, but that's pretty much OK- you've designed in the passive gains to pretty cover the whole-house heat losses during the shoulder seasons, right? Anything less than ~R5 will be a comfort issue for bare feet. If less than ~R2 you have potential condensation/mold issues under wood flooring or rugs during the summers, keeping the basement using 75F, 65% RH for upper bounds.

A small condensing gas furnace makes sense- they're cheap & efficient, and in a high-R house the cush-factor of radiant is nearly non-existent (most of the time the floor would only be a degree or two above room temp, and not particularly warm to the feet) and since you're in a forestry-rich region pellet burners are probably reasonable too. Bear in mind that with high R and reasonable thermal mass with a well-modeled design surrounding the solar gains, the bulk of your cooling load will be dehumidification, not sensible cooling. Whatever AC unit you put in there needs to have an efficient dehumidification mode, which won't necessarily correlate well with a high SEER number.

my logic for going 2x4 wall & 4" of exterior foam was that I think the foam is one of the most critical pieces of the puzzle.  2x6 walls & similar amount of foam would be a seriously thick wall.  My assumption was that it made the most sense to limit the thickness to 8" or so (just a number that I came up with) so within that thickness, I'd rather have more on the outside to maximize the sealing & minimize bridging.  A 2x6 wall 24OC with 2" would probably work too, though...

Good point about the AC & dehumidification.  This past summer was a bit of an extreme for our area, but we had the AC on & the windows closed for well over a month with no break..

Dana1 i am wondering why you would not just go with a higher R value with an ICF? Go straight up from the footing to the roof. It is fast and simple. I know that Logix is offering ICF's with an R value up R74. After you have done a double stud wall and added another couple layers of foam to the exterior you have just lost the job, because of construction time line and cost. Simplicity and speed is going to be just as big of a factor in the future.

It's mainly cost, after-the-fact flexibility for the rest.

I've NEVER advocated double studs AND exterior foam as you seem to imply (which would be more costly indeed.)

Single studwall + fat foam seems to be a sweet spot for build-ability up to ~ R40. Once you've gone to double-studs the cost of extra R (without adding foam) is low, but the labor cost of the framing nearly doubles, AND it's easier to screw up the details. 2x6 studs & fat foam are easy.

The cost of ICF has been coming down, but I've yet to see it competitive on cash against other methods in a high-R wall, or even an R30 wall. You end up with a MUCH stronger and MUCH quieter building for the money though. In a very-simple form-factor it might be easier to make the numbers work.

Show me the numbers, and without the sales-droid's thumb on the scale, where all cellulose is a paltry R3/inch with an installed cost of a buck a pound, all EPS is R 4.5/inch(when used in ICFs) and concrete forms never blow out (especially on 2 story structures), ready-mix is always under $100/ yard, and the thermal mass of the concrete nearly doubles the "effective R", the framing carpenters are always threatening to strike, and the forms are put up & concrete is always poured by docile, imported, low-cost labor... :-)

Change-orders or corrections on window & door openings get kinda interesting out there in the real world of concrete walls too.

jerkylips: Building walls this thick is no big challenge, and nothing new. A typical 2x6-framed brick-clad home with a 1" cavity is usually getting on close to a foot between the interior paint and the dew on the brick face, a very common stackup. A 2x6 with 3.5" of iso and rainscreened clapboard or vinyl siding comes in about the same.

Dana's statement have basically been my findings as I have gone down the ICF road.  For a DYIer, the prices are super high (to pay in relation to framing yourself) and if not, the stakes are even higher on a screw up.
I get the quietness and the strength, but I am yet to get the R value claims, especially since the concrete in insulated on each side.  Basic concepts of thermal mass void this argument right away.
I can buy the lumber and foam to construct an air tight, R-35+ house for $5000.  24,000 is my lowest ICF bid for the same walls.  Sure, that is installed, but materials alone are 15,000.  Even DYI it doesn't make as much sense.  THe next step down was urethane SIPs, 6" for the house walls, and 4" for the garage, with the 6" being around r-40ish they claim.  This came in around $13,000 delivered with everything needed, not installed.
If I were paying a framer, this would start to make much better sense, but I am still debating if the extra 8k is worth the speed.  It just might be since we will be renting.

Hi,
This information is helpful to every one for the best building result..
Thanks for the information that you shared with us here..