you can get away with a lower R-value if you used foam over other insulation choices.

No building inspectors in Ithaca/Syracuse?

Yes, you do get better sealing with foam than many other forms of insulation. But better sealing is not the same as R factor. Still, in your cold climate you're only cheating yourself by trying to "beat" the Code. Indeed, leading building scientist Dr. Joe Lstiburek advises R40 for any wall north of the Mason-Dixon Line.

"Flashing" foam for a good air seal, then using blown or batt insulation is a way to improve insulation effectiveness without throwing dollar sense to the winds. But with the difficulty in getting a uniform thickness, I wouldn't go with less than 2" of foam, then all the blown cellulose you can fit in on top of it.

There are a number of sound choices for the cathedral ceiling. See Link below.

I would absolutely not spray foam at below 0 degrees C. as the edges shrink back. (Unless the contractor agrees to touch them up with a second application.)

Here is a link that might be useful: Building Science Corp. on conditioned attics

CORRECTION:

I just checked (NY State building codes) and I was incorrect with the ceiling minimum values. It should be R-49 NOT R-38.

Here are the full requirements, as updated by the Energy Conservation Code of New York State

Note the minimum windows and skylight factors. Incidentally, Dr. Lstiburek recommends R60 for attics north of the Line.

I am not an expert, but I have some experience to share. My parent's own a plastic company (whom I work for) that uses foam insulation for a large percentage of the products manufactured. We have been using a variety of spray foam for a LONG time...way before the trend for foam insulation started sweeping the nation. We conduct regular testing, and are constantly searching for a better/newer/more efficient/cost effective foam. We dabbled with Soy, but had to discontinue after R&D trials because the Soy foam was not 'forming' or expanding as it should, and was losing considerable volume after time. Yes, its "greener"...but I would definitely do some very good research on this before moving ahead with this type of foam insulation.

We are building right now and we also live in a cold climate. We get some chilly winters that seem to last about 9 months of the year, LOL. We have geothermal, closed loop system with one 3 ton unit for radiant floor heat in garage and basement, and two 3 ton units for house. We used a 2 lb. closed cell in 2x6 walls, around windows, doors, joists, etc. We sprayed certain areas in the attic with foam (rafters and around the 2nd air exchanger unit that is located up there) in conjunction w/blown in cellulose. We used 2 lb. closed cell for garage walls and garage ceiling. We only used fiberglass for sound insulation on certain interior walls.

Do NOT attempt to spray foam if the space is less than 50 degrees F!!!! Product in drums will not interact as it should, and you will end up using a lot of product for minimal volume. Waste of money as the 2 lb. closed cell is VERY expensive....but I'm sure you already know that. HTH.

Obviously the "getting away with lower r-values" doesn't apply to code requirements as Worthy states.

Spray foam is still a very expensive way to meet insulation needs. If I were building in your climate, I'd do fiberglass covered with foam sheathing for the walls. In the attic, I'd spray 2 inches for air sealing and do blown to r-50 to r-60. My only question is that at really low temps, there are some issues with blown insulation but that may only be for fiberglass. Really, I'd probably do blown on top of good air sealing rather than the 2 inches of foam.

I'd stay away from conventional fireplaces, no recessed cans on the top floor and I'd get a blower door test. Then if I had more money to spend, it might be on triple pane windows. I'm not really sure I'd ever go to spray foam - I'd up the walls to 2 inches of rigid foam or go to 2x8 (staggered 2x4s) before I'd spray the walls.

But maybe foam is cheaper in Ithaca. But around me for the price of spray foam, I could do so much better with fiberglass products and rigid foam.

for your climate, 1" for sure, and 2" is pushing the line of interior wall condensation. The numbers would have to be ran for sure, but 2" MIN. of spray foam should be used. Using closed cell on the exterior sheathing promotes inward drying, so enough "r" of closed cell needs to be on the exterior face to keep your dew points at the correct level. closed cell should be used for air sealing like this. Open cell is water permeable and is not as an effective air sealer as closed cell. The other option is to spray in a dense fiberglass (around an r4 range). This will not settle like cellulose can, and is much better then batts. I would also shoot it in the attic hitting an r50-60 as well. Fiberglass is less weight compared to cellulose, which reduces gyp board bow and possible screw popping in your ceiling.
Given the fact that you are already built to the point of insulation and efficiency as an afterthought, (2x6 walls w/ integrated foam siding is not considered efficient, sorry but rather barely code compliant), I would probably do 1 of 2 options. First, if doing net and blow cellulose/fiberglass, air seal like crazy. Ask your insulator to give you a price, or do it yourself. Caulk every stud to the sheathing, at the sill plates all exterior wall penetrations, wires going into outlet boxes, water lines, etc etc etc. Then blow in fiberglass. This will give you an r some where around 22 (clear wall performance more around r-16) but reduce your air infiltration quite a bit, which is your NUMBER ONE largest robber of energy. You can put 30" of insulation in the wall, but if your shell is leaky, its all for nothing.
If you would like to spend a little more and get it a little bit tighter, then do 2-3" min of closed cell foam, then follow it with fiberglass net and spray. I never recommend batts because they are leaky, and do not fill all of the gaps (especially around electrical.

also, as a side note, energy code is changing in April. And next year it will be required to be 30% more efficient then this years energy code, which is honestly laughable as is.

Thanks all for the input. Here's an update:

We called the manufacturer of Agribalance today and he informed us NOT to spray directly to baffles in the ceiling and to either spray directly to the undersiding of the roof (thus making it non-vented) or just use another form of insulation on the attic throughout the whole house.

The more we read the more we get confused because a lot of insulators seem to have differing opinions.

We have decided on the following:

1. All the exterior walls will get 3.5 inches of closed cell giving us roughly R23. The foam should seal off any "leaky" areas and the exterior siding with backing will take care of the thermal leaks via the studs.

2. The ceiling's in all the attics will get sprayed with open cell around all potential "leaky" areas and then 16" of blown in cellulose will be applied which should give us R-50+ in the ceiling. Since we have no HVAC equipment or HVAC vents in our attic there is no reason to insulate the entire envelope. We will never finish the attic space anyhow since it's mostly a 12/1 pitched attic and just too high up to use. We have a ridge vent on the entire roof so the area will just naturally ventilate itself.

This has been a really tough choice and further opinions are welcomed since we're still a few weeks out from insulating.

I wouldnt waste you money on open cell in the attic. It is not going to block leaks much better then 16" of cellulose. Also see my notes about cellulose and the weight...

Just noticed you're only proposing R14 on the basement rim. Current US Department of Energy recommendation for your area is R30.

You can also use the foam for the second floor rim, floors between conditioned space and an unheated garage and any other odd spaces you may come across.

Get the most recent issue of Fine Homebuilding and look at the article on shallow spray foam for sealing and something less expensive for R-value.

This is the 'flash foam' method.

It is VERY important to make sure the dew point is INSIDE the foam and not in the fiberglass/cellulose/etc. R-value layer.

Worthy,

I forgot to mention that they are putting R14 on the basement walls but also R16 in the flooring (basement ceiling). Since we have radiant flooring PEX we will be putting in 1/2 inch of DOW reflective board (Roughly R3) and R13 batting.

are you doing tubes in the basement floor as well?

If it's an unheated basement, why insulate the walls? If it's heated, why insulate the basement ceiling?

Batts on the walls invite mould and mildew problems. And if the insulation is sprayed or boards, you have to cover it with a thermal barrier--usually drywall. So you have a largely finished space already.

As well, R25, at least for the upper four feet, is recommended by the US Department of Energy. See link. Input your zip Code.

Here is a link that might be useful: US Dept. of Energy Zip code Insulation recommendations

EzStud - I live in Ithaca too. Can I ask who your CG is? Would you recommend them?

worthy/lzerarc,
Yes the basement is heated (well 2/3 of it is). My contractor has said if we are going to finish the basement then we should forego the insulation in the floor and insulate the basement walls (as long as we run the heat in the basement).

svs128,

Our builder is really a good builder. His work is meticulous and he's honest which is hard to fine. That said you still have to do your homework to make sure any builder/installer stays on target.

All that said I would recommend him in a minute. If you want his information I will post an email address for you to contact me.

"The house will be completely wrapped in Tyvek and we are also using an insulated backed siding from Alside which provides another R-5 of insulation behind the siding. Our attic space is free of venting and HVAC equipment. Our roof has a ridge vent for breathing."

we put our reflective sided closed cell foam sheathing on the exterior of the walls. foam board caulked at top and bottom, all holes sealed prior to cladding install.
this in conjunction with caulking the sole plates begins and insulated and air sealed wall from the exterior.
in my climate we use 1' closed cell foam sheathing.
this reduces thermal bridging..2x's are approx 1R-value per inch..R value of 2x6=5.5 a big reduction of insulation value.2x6 construction allows for R-19 of conventinal insulation add the closed cell foam sheathing and your wall value increases to R-25
combine this with air tight drwyall approach to interior of walls after insulating with conventional insulation.

this I've found is a better use of $$ for foam in walls.

we don't see many houses who foam seal the attic floor..since we so stupidly put our ducts and mechanicals in the attic..we mostly foam insulate the roofline..costly dependint on roof pitch.
but by foaming the attic floor to air seal and then installing conventional insulation over it..as in your specific case, this is a good idea.

the goal is to stop air leakage through the insulation so that it can perform as designed.
my goal as an energy rater is to determine the most cost effective way to do this.
foam in the walls is costly, and does nothing to reduce thermal bridging of framing members..think about it corners and tees..window framing..overall the thermal bridging reduces walls R-value by approx 20%

you can still add the foam sheathing over the houswrap.
and since the foam is continous it will perform better
and make the wall tighter than an insulated siding.

best of luck

overall the thermal bridging reduces walls R-value by approx 20%

I wouldn't be surprised if high density fg batts with 1" sheathing provided a better R Value than the spray foam without XPS sheathing.

with foam sheathing you get a uniform R-value
not so with foam sprays
the install is usually an overall fill value..2" to 3.5" with peaks & valleys.
so the conventional insulation and foam sheathing boards
provide a known R-value.

the contractor that I refer clients to overfills walls shaves back foam so that foam is in continous contact with sheetrock and R-value is continous.
not many foam companies offer this.
I don't recommend foam sprays for walls, but sometimes the customer wants it. I do remind them of the high cost, and the long long payback.

best of luck

Insulating the exterior walls and ceilings of unheated garages with no conditioned space above is one of those things that seems more popular with diyers than building pros. (Unless, of course, you plan to condition the space, especially in the winter.)

Owens-Corning, which one would think would encourage using more insulation everywhere, in fact, says it's a questionable idea, as it creates a hot box in the summer; the insulation traps the ambient heat, including that from any cooling car motors in the garage. I would suggest it's ditto the reverse in the winter. Unless, of course, your house is so leaky that it's heating the garage. Better than insulating unconditioned space, spend that money on better sealing your living space.

Here is a link that might be useful: Insulating a Garage