I am lower part of D...

They got a 3 ton from 2x6 walls with 2.5'' of closed cell spray foam....

I went to look at ICF homes yesterday and I really liked what I saw... now I am trying to see how much it will cost me...

and yes they do have a layout of the house with the windows and everything... I don't know the specific windows at this time because we haven't sat down and really talked about windows yet.

Personally, I would go with either rigid foam over 2x6 studs or with ICFs. Compared to careful sealing and preferably two air barriers, spray foam isn't cost effective. I have no doubt that SIPs work well too.

I think going for really high r is only part of the new home building equation. Like others have pointed out, other systems have various advantages (or cons) that also need to be compared. Too much focus is always placed on the r values IMO.  I decided to go with vertical ICF (hobbs) as they are locally produced, maintain a pretty high r (advertised around r-30, but I realize clear wall and flat wall will reduce closer to r-22-24), but they are "greener", air infiltration is basically eliminated at the icf locations, strength (we are in tornado alley) and I also think it will allow the house to go up faster with eliminating layers and steps to be similarly air tight and have a high r.  I also explored SIPs (urethane, close to r-40 panels) and were going that route until my local manufacturer closed the doors and the price nearly doubled to ship others in here.  I have framed many houses, so that is the "safe" route, but I want to give ICF a try for the reasons above. (foundation to roof)

Posted By petrey10 on 08 Jul 2011 04:56 PM
I am lower part of D...

They got a 3 ton from 2x6 walls with 2.5'' of closed cell spray foam....

I went to look at ICF homes yesterday and I really liked what I saw... now I am trying to see how much it will cost me...

In lower zone D your 97.5% design temps are probably in the very low negative single-digits, so some split air source system could still be good for the primary heating system but not all if you get the heat loads low enough.

2.5" of closed cell between the 2x6 studs is below IECC code-minimum for your area, even if you assume R6.5 per inch on the foam you're only at R16 before thermal bridging, and only about R12 for whole-wall R- about the same R value as if you'd used 2x4 studs and 2.5" of closed cell.  The only difference is you'd have 3" of empty space in the cavity rather than 1" of empty space.  This about the worst application of a spray-foam budget you could make.

The low whole-wall R is because of the thin 2.5" deep section of thermally bridging stud, which come in at less than R3, (best-case species!) Better to fill the entier cavity with something cheap, and put the foam on the exterior where it insulates over the R5-R6 stud for a much higher whole-wall R.

With a full 2x6 cavity fill of low density wet-sprayed cellulose you'd be at ~R14 whole wall, ~R15 if advance-framing is used.  If you then put the same 2.5" of closed cell foam on the exterior you'd be up to R30, and the quality of the air seal would be an order of magnitude better. 

Cut back to only 2" of exterior foam and you're still over R25, and the total cellulose + foam insulation money is about the same as what you were looking at with the 2x6 with 2.5" cc foam cavity fill, and you've cut the heat loss from the wall area in half. (Not to mention the lower air infiltration factor.)  With R12 whole wall and U0.34 glazing of modest or typical fraction, the wall loss was likely greater than the glazing loss, so but taking the wall up to R25+ it's tipped strongly the other direction. But overall it's probably cut your 3 tons down to 2, and with some tweaks you could probably get it down to 1.5 tons without having to live in the dark.

ICFs are usually a pretty big up-charge on structural cost over timber framing, and still a significant cost-adder on the insulation at equivalent whole-wall R compared to a 2x6 framing + exterior foam approach.  They're a lot stronger and a lot quieter though.  You'd still need to pay close attention to air-sealing to make them truly perform, and you'd still want to go at least R60 on the attic, and R10 (min) under the slab.  R16s are about as low as you can get, but R20 isn't a huge cost adder. It starts to add up when looking at R25+. EPS tends to run 40cents/square foot /inch of thickness (and I'm assuming it's no cheaper in ICF than as sheet goods) and it's about R4/inch. The insulation cost of the first R14 whole-wall (cellulose in 2x6 framing) is about 3x as expensive in EPS as it is in cellulose. But  the next R13 would only be about 2/3 that of closed cell spray foam. The whole insulation portion @ R25 is probably about a third more if ICF, compared to 2x6 + ccSPF, but the structural package is even more.  Insulating stick-built with rigid goods is usaully quite bit cheaper than with spray foam too (but requires more air-sealing details.)

Someone should make a hollow core SCIP (concrete/foam/concrete) that can be filled with cellulose.

Posted By jonr on 11 Jul 2011 11:51 PM
Someone should make a hollow core SCIP (concrete/foam/concrete) that can be filled with cellulose.

Using a hygroscopic fiber in concrete slab sandwich might have some serious issues if it ever got wet, which is probably why they only make them with foam cores.

Nothing new there - lots of walls have problems if the cellulose gets wet.

Not all sheathing materials are as porous as concrete. Ripping out some gypsum to repair & replace wet insulation when wetting occurs doesn't compromise the structural elements. Stud bays limit the amount of lateral travel of the moisture. Being able to use cellulose in a SCIP would require higher complexity than a straight ahead foam-sandwich approach, which would probably eat up any potential cost advantage it might otherwise have over polystyrene.

ICF up charge is only 5% for my project... we are going with it.

2.5'' of foam on inside and outside with 6'' of concrete down the middle...basement all the up to the roof

our local COOP has records of 3 homes in the area that are ICF and Geothermal. These houses are being heated and cooled for under 700 bucks for the YEAR.... Two houses were 4500 conditioned space and one was slightly smaller in the 4000 sq ft.

What size of windows should I be going with.... as of right now our builder has 3'by5' windows... they seem BIG but maybe they aren't

Hi, i newly joining in this forum community, i am totally confused about this matter. Please appreciate me.

What size of windows should I be going with.... as of right now our builder has 3'by5' windows... they seem BIG but maybe they aren't

All other issues about windows aside, you are going to want BIG(ger) windows with ICF because of the substantial wall thickness. Windows that might be fine in normal stick-frame construction seem too small for the massive ICF walls. Currently, my ICF windows run from 2' X 2' up to 12' wide X 7' high.

For example, I added a window that is 3' wide X 1.5' tall on a whim in order to let some light into a dark area. For security reasons I wanted to keep it small, but after seeing it built out, the 18" dimension is too small. If it was in an any more visible area I would cut it bigger. Another stick frame home i have has a number of windows that are only 1' wide and they look fine.

While we are at it, interior window sills take on a whole new (dimension) with ICF construction. I have seen many different treatments, including putting granite on the sills and even using them as seating or display areas. Be sure to visit an ICF home early on so you know what to expect in terms of the differences.

ICF up charge is only 5% for my project... we are going with it.

I am curious as to how that number was arrived at for you. Does it represent the difference between actual quotes using either ICF or stick-framing?

I recently put my own house together using timber! we also added multiple timber stables in our field.

Posted By petrey10 on 08 Aug 2011 02:18 PM
ICF up charge is only 5% for my project... we are going with it.

2.5'' of foam on inside and outside with 6'' of concrete down the middle...basement all the up to the roof

our local COOP has records of 3 homes in the area that are ICF and Geothermal. These houses are being heated and cooled for under 700 bucks for the YEAR.... Two houses were 4500 conditioned space and one was slightly smaller in the 4000 sq ft.

What size of windows should I be going with.... as of right now our builder has 3'by5' windows... they seem BIG but maybe they aren't

That's about an R20 whole-wall with a modest amount of dynamic-performance enhancement from the thermal mass. It's not superinsulation, but at least it meets code (which wasn't the case in your skimpy foam-in stick framing.)    Unless you go wild on window area that should peel a bit off the size of your geo too.

DO be careful on upsizing the glazing- make the case for every square foot, otherwise you start to spend way more than 5% more to keep the total heat loss the same as a smaller U0.30-0.34 type window.  Use fixed windows where you can, and casements elsewhere, or you risk blowing the very good air-tightness aspects of concrete construction. (Sliders & double-hungs are usually the poorest performers.)

Also,  be sure to insulate under the slab to at least R8 (2" of EPS), and float it- keep the interior foam of the ICF intact as a thermal & capillary break rather than putting concrete-to-concrete.

5% more than stick built using 2x6'' studs.... windows are single hung 3'x5' in most places... smaller in certain areas...


upsizing the glazing?? i have no clue what you are talking about....

Posted By petrey10 on 10 Aug 2011 06:33 PM
5% more than stick built using 2x6'' studs.... windows are single hung 3'x5' in most places... smaller in certain areas...


upsizing the glazing?? i have no clue what you are talking about....

upsizing the glazing ==> increasing the size/number of the windows (or overall glazed area.)

Increasing the glazed area of an R20+ wall decreases the thermal performance of the wall, since the glazing becomes the dominating heat loss factor, since a pretty-good U-0.33 window is an R3 hole in your R20 wall, with six times the heat loss per square foot.   A single 3x5 window has the same heat loss as 90 square feet of blank wall, or roughly 10 running feet of single story exterior.

Going to ever lower U-values to make up for larger window area get's very expensive very quickly- it's possible to buy windows with U-values under 0.20  (==R5+), but it's quite expensive.  From a cost/performance point of view it's useful to make the case for every square foot of window or U-value against the increased sizing of the geo required to support the additional heat loss.  On south facing windows it's also useful to optimize both size & coating type for wintertime solar gain (not  just heat loss and geo sizing) since any vertical south facing double-pane will have a net energy gain at your latitude.  (You'd need to provide for shading any upsized south facing glazing in summer as well, or the cooling load can go stratospheric.)

Single-hung windows offer barely half the ventilation & egress area of casements, but are generally tighter than double-hungs.  It's still easier to get a good air seal on casements & awnings than any sliding-sash window.

hi just joined the conversation and it is so confusing as no clear idea is there for the anyone. to the point and helpful conversation is better for achievement. hope to get some results over. los angeles fumigation

it is so confusing as no clear idea is there for the anyone

Unfortunately, in green building, no one particular solution is applicable to everything.

Wife and I built an ICF 2200 sf ranch house with full basement with R22 whole wall from footing to eaves in the northern edge of Zone D in Illinois. I used triple pane casement windows (U.25), minimizing glass area to meet code (8% of floor area) and added insulated rolling shutters on south and west facing windows for sun control. Ceiling is R50 using 3" of sprayed urethane closed cell insulation and batts. Basement floor is insulated to R10. Total heating energy efficiency was measured at 2.0 BTU/SF/HDD. I cool house all summer using 1-1/2 ton central A/C and maintain 50% relative humidity using whole house dehumidifier. July's electric bill (ComED) was $64. Last January's natural gas bill (heat, domestic hot water and clothes dryer) was $104. Annual homeowner insurance premium with $2000 deductable is $320. The cost adder to go ICF was easily 5% over conventional 2x4 stick construction, but since we plan to live here for many years, we expect to recover the upfront cost premium in time. Improved comfort, noise attenuation and security (greater strength of construction) are immediate benefits that I would not want to do without.

So at 2btu/ft/HDD x 2200' you're talking 4400BTU/HDD...

...which is 4400/24= 183 BTU per degree hour, (base 65F.)

Assuming a 97.5th percentile heating design temp (appropriate for moderate-R, high mass construction) of 0F it means your design heat load would be:

183 x 65= ~12000 BTU/hr (good job!)

...which can be delivered by almost any 18000 BTU mini-split at 0F.

It's possible that with an optimally open floor plan the heating, AC, and whole-house dehumidifier mechanicals could all be rolled into a single 1.5-2-ton mini-split (or multi-head version) for well under $10K.

I'll bet the whole package was considerably beyond 5% more expensive than a code-min R13+5 2x4 stick built (but it seems almost a crime to build the latter.) Sounds like a great house! What to you mean "...recover the upfront cost premium in time...", you already HAVE recovered the cost, in the comfort & security going forward- it's a house you actually want to live in, not a code-min piece of crap you're desperate to get out from under, or to flip for quick profit when the housing market picks up.