ICF Homes Acheive Net Zero at $110 per sqft cost
Last Post 06 Jul 2015 09:59 AM by smartwall. 18 Replies.
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LbearUser is Offline
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03 Jun 2015 04:09 AM
ICF MAGAZINE ARTICLE

New Paltz, NY -

  • Nine homes built using ICF attained Net Zero certification and had air tightness levels of 0.14 - 0.28 air changes per hour at 50 Pascals (ACH50).
  • Qualified for LEED-Silver
  • HERS index of 7

2,288 square feet built for $110 per square foot and entire home completed and ready to move in within 5 months


gosolarUser is Offline
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03 Jun 2015 07:40 AM
See the duro rock on the exterior of foundation?

Why?
jonrUser is Offline
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03 Jun 2015 11:18 AM
Above grade, I'd guess to protect the foam.
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06 Jun 2015 03:16 PM
It's a good example project that shows that ICF can be done on a budget and competitive to other building methods. Also with the short building time from ground breaking to occupancy of 5 months which reduces building costs. Extended building times makes for more expensive overall building costs. Time is money.
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07 Jun 2015 01:32 AM
$287,000 divided by 2,288 sq ft is $125/sq ft. How do they come up with $110/sq ft?

Also they say, "Construction was staggered so the pump truck could pour multiple projects at each visit." That's a cost savings that's not going to be available on the usual one-off ICF home build. This article discusses an ideal construction situation which is not going to be the norm with ICF projects.

I wonder how much the other houses in the project cost per sq foot, and how much, if any, cost shifting from this house to some of the others may have done like by not allocating block shipping costs to this house. The article, to me, smacks a little of being a sales pitch.

Even a retired engineer can build a house successfully w/ GBT help!
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07 Jun 2015 01:46 AM
Posted By dmaceld on 07 Jun 2015 01:32 AM
$287,000 divided by 2,288 sq ft is $125/sq ft. How do they come up with $110/sq ft?

Also they say, "Construction was staggered so the pump truck could pour multiple projects at each visit." That's a cost savings that's not going to be available on the usual one-off ICF home build. This article discusses an ideal construction situation which is not going to be the norm with ICF projects.

Next to the square footage information, it states, "floor":

Size: 2,288 sq. ft. (floor)


So maybe the square footage doesn't take into account the basement area and with the basement the square footage is 2,609 sqft?

Even so, at $110-$125 per square foot, that is a darn good price for a Net Zero home that will see basically zero utility costs per year to operate the household electric.


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07 Jun 2015 12:04 PM
No basement. From the pictures they poured the gables separately, which is a separate pump pour. The windows are mounted on the outside of the shell. Could have saved some money by pouring the footing, frost walls and slab in a single pour and skip the PUF for a much more affordable eps under slab. Not very efficient. Could be done cheaper. Trying to figure out the Durock. Any guesses?
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07 Jun 2015 12:56 PM
Posted By smartwall on 07 Jun 2015 12:04 PM
...Trying to figure out the Durock. Any guesses?

I assumed it was there for protection of the foam below the siding and above grade.   Parge the top 12" or so of the Durock with surface bonding cement or cement plaster and it looks like a poured foundation wall and weedwackers won't damage it.  I'm not sure why they ran it all the way to the footing though.
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07 Jun 2015 01:42 PM
The article states it required 8 days for the ICF installation. How many man hours are they really talking about? I am getting ready to start my ICF construction on a 2,000 sq ft. house with the same size unfinished walk out lower level, and I would like to know approximately what my labor cost (manhours) would be. I will be using ICF all the way to the roof line like in this home.
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07 Jun 2015 08:28 PM
Based on my experience of building one 2000 sq ft single story house I would say the labor to cut and stack the blocks is one of the lesser costs of the whole project. Everything else is what adds up. Now, if what you are asking about is the labor to fully construct the ICF walls, including door and window bucks, placing the concrete, putting in all the access tubes to pass plumbing and wiring through the walls, installing floors so have a platform to work the next level, and on and on then that number will vary widely depending on a whole slew of factors. For me, from excavation to closed in was on the order of 4 to 6 months with only 2 of us most of the time.
Even a retired engineer can build a house successfully w/ GBT help!
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08 Jun 2015 02:47 PM
They're probably getting similar scale-discounting on the geothermal heat pumps and rooftop PV systems, which may start to look affordable after both Federal and NY state incentives are applied. You're probably talking $30-50K of GSHP (pre-subsidy), and $25-30K of solar (pre-subsidy), which would be a pretty huge chunk of the budget without the subsidies.

Sprayed 2-3lb density R20 foam nder the slab seems a bit silly given the much lower cost and much lower environmental impact of EPS. Even with EPS, R20 sub-slab would be a but silly unless it's a heated slab. If the R60 foamed roof is also closed-cell polyurethane between rafters they aren't doing the planet much if any favor with these houses.
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09 Jun 2015 09:47 AM
I agree. I received a quote of $.37 per sq ft for 1.25 lb reclaimed eps 4" thick. Heck of a lot less than the spay foam at what $3-4 per sq ft. The attic could have been r-60 celly for about $1.25 per sq ft if you used a raised heel truss set between the icf walls
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28 Jun 2015 11:48 PM
One thing to note is that one should not skimp on the ceiling R-Value. ICF's provide the wall strength, R-Value and thermal mass but ceilings are very important. This home has an R-60 ceiling area.

Energy loss through the ceiling/roof accounts for about 30% - 40%. Skimping on R-Value in the ceiling/attic is not a good thing in an energy efficient build. That is why this builder went with an R-60 ceiling area and the ICF (R-23) walls.

When one spray foams a roof area one has to take into account that the roof trusses are thermal bridges and if they are spaced 24 inches apart, that is a thermal bridge every 24" and a reduction in the total ceiling area R-Value. An attic with the insulation on the ceiling plane and the not the roof plane does not have to deal with the thermal bridging of the roof trusses. Of course the latter would result in an unconditioned attic which is OK if your duct work is not located up there.

 
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01 Jul 2015 05:51 PM
Posted By Lbear on 28 Jun 2015 11:48 PM
One thing to note is that one should not skimp on the ceiling R-Value. ICF's provide the wall strength, R-Value and thermal mass but ceilings are very important. This home has an R-60 ceiling area.

Energy loss through the ceiling/roof accounts for about 30% - 40%. Skimping on R-Value in the ceiling/attic is not a good thing in an energy efficient build. That is why this builder went with an R-60 ceiling area and the ICF (R-23) walls.

When one spray foams a roof area one has to take into account that the roof trusses are thermal bridges and if they are spaced 24 inches apart, that is a thermal bridge every 24" and a reduction in the total ceiling area R-Value. An attic with the insulation on the ceiling plane and the not the roof plane does not have to deal with the thermal bridging of the roof trusses. Of course the latter would result in an unconditioned attic which is OK if your duct work is not located up there.

 

Not really only very rarely. 

Even in code-min single story homes the roof has less total area than the wall area, and a lower U-factor than the wall area, with roof losses being 15- 20 % of the total losses tops.   In two story  houses the roof area is even smaller, and the fraction of the total even less.

In high-R homes the U-factors of walls and roofs are usually closer than in code-min homes, but in those houses window losses usually are a much bigger fraction.

A code-min roof/attic in that part of NY is R49 (or a max U-factor of U0.026, which is R38 whole-assembly after thermal bridging.)  Most code-min attics with trusses are done with blown fiber that buries the truss chords, which is a very good thermal break, just as good as encapsulating the rafter elements of trusses with R49 (or R60) foam, beating U0.026 with ease.

The difference in heat loss between a code-min R49 roof an R60 is real enough, but it's small compared to the difference between R20+5 code min (or U-0.048, which is R21 whole-wall) and an R23 ICF mass-wall, which could have been an R15 mass wall and still met code in US climate zone 6.  The raw U-factor of the R23 ICF is about U0.042, and would have met code even without the thermal mass boost.
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01 Jul 2015 07:36 PM
most attic trusses, manufactured ones anyways the top chord or pitch chord is 2x4 or 2x6 material not like rafters so they would get buried in the spray foam insulation - no thermal bridging(TB) there, unless of course you are using rafter framing 2x10 or larger, then you would have some TB, in those cases we use TJIs for rafters, that virtually eliminates TB, my preference is SPF still though, it creates an unvented attic - really works well with the investment you have put into the ICF walls, but yeah the roof is not the place to skimp agreed! it creates a kind of air buffer too, i have been doing them for over twelve years now and SPF has come down ALOT especially the open cell, which is what i prefer, not to start a whole new debate there but if i get a leak in the roof i can find it quicker plus it seems to me that with the temperature variations in the roof system i see more separation with the closed cell foam than i do with open.
so i dont have all the fancy numbers and derivatives but i have built alot of them and lived in a few, i specialize in Net Zero utilizing ICF and well it works, but thats just me and my two cents, hope that helps.
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02 Jul 2015 12:10 PM
Posted By billnaegeli on 01 Jul 2015 07:36 PM
most attic trusses, manufactured ones anyways the top chord or pitch chord is 2x4 or 2x6 material not like rafters so they would get buried in the spray foam insulation - no thermal bridging(TB) there, unless of course you are using rafter framing 2x10 or larger, then you would have some TB, in those cases we use TJIs for rafters, that virtually eliminates TB, my preference is SPF still though, it creates an unvented attic - really works well with the investment you have put into the ICF walls, but yeah the roof is not the place to skimp agreed! it creates a kind of air buffer too, i have been doing them for over twelve years now and SPF has come down ALOT especially the open cell, which is what i prefer, not to start a whole new debate there but if i get a leak in the roof i can find it quicker plus it seems to me that with the temperature variations in the roof system i see more separation with the closed cell foam than i do with open.
so i dont have all the fancy numbers and derivatives but i have built alot of them and lived in a few, i specialize in Net Zero utilizing ICF and well it works, but thats just me and my two cents, hope that helps.

Open cell polyurethane uses about half the polymer per R of closed cell, and uses water as a blowing agent instead of HFC245fa (which has a global warming potential of ~1000x CO2).  Until vendors move over to the HFO1234_ _ low GWP blowing agents, a high-R closed cell roof  or wall does more lifecycle damage than the energy use it is offsets.

It's often cheaper than fiber blown in netting, but still a heluva lot more expensive than a couple feet of open blown cellulose on an attic floor.  ocSPF is typically 11-13 cents per R-foot2, installed compared to 3-4 cents per R-foot for open blown cellulose.  Unless the attic is being used for storage or mechanicals, it's usually cheaper/better to go with a vented attic and cellulose, and air-seal at the supporting layer for the cellulose. Half-inch OSB ring-shank nailed to the under side of the truss chords with the seams taped & mastic-sealed makes a substantial  no-sag support layer, air-barrier, and "smart" vapor retarder capable of supporting even R100 cellulose without sagging (but pay attention to the dead-weight loading specs on the truss chords when going higher than R75, or for wider spans).

Designing for an "extra" 6-10" of wall height to allow a horizontal service chase between the insulation layer and the finished ceilings works pretty well.  In a high-R/Net-Zero house that's sufficient space to use mini-duct mini-splits for heating/cooling for better distribution in doored-off floor plans.

Even when you account for the cost of the OSB layer and the service chase, it usually pencils out favorably to an unvented attic approach using ocSPF.   With ocSPF in an unvented roof it's also often necessary to use an interior side vapor retarder to avoid moisture-cycling issues into/out of the roof deck summer in climate zones 3 & higher, that requires actively ventilating the attic space with conditioned space air, and potential roof rot issues in zones 5 & higher from wintertime moisture accumulation.  Sprayed on "vapor barrier latex" doesn't perform to spec when applied directly to ocSPF, so it adds the cost of a gypsum layer onto which the vb latex can be applied, which is a cost-adder beyond the insulation itself.


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04 Jul 2015 05:07 PM
Dana,


With a truss roof at 24" o.c. in a single story (3,000 sqft) and 5" of open spray foam. What would the whole roof calculation be taking into account thermal bridging?

My rough calcs show R-15 whole roof area average.
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06 Jul 2015 09:59 AM
Your probably going increase that average, because the foam is going to adhere to the sides and edge of the rafters. In fact it's impossible for it not to, very messy stuff
smartwallUser is Offline
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06 Jul 2015 09:59 AM
Your probably going to increase that average, because the foam will adhere to the sides and edge of the rafters. In fact it's impossible for it not to, very messy stuff. Maybe not a full 5' but because of the adhesive nature of the material, pretty close.
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