I'm all for the foam board on exterior of walls.
conventional insulation in walls.
air tight drywall approach to interior of walls.

what for attic insulation?
cellulose may slow air flow..but it doesn't stop it.
putting cellulose in the attic isn't my choice
ever. the small dustlike particles find their
way into the house via every small crack/gap/
hole. as we make lots of holes in ceilings...I'd
look at other options.

best of luck.

Re solar PV, all I can think of was my visit to Ft. Clatsop where the poor Lewis and Clark guys didn't see anything but rain the entire time they were there.

You should check a solar insolation map to make sure your area will provide enough sunshine to make the solar pay off....

Everything we read on going green said to put your money first into insulation as, no matter how you generate a btu, the longer you can hang onto it, the better.

Have you looked into ICF? Over at greenbuildingtalk.com they have a forum on ICF. You'll be able to reduce the tonnage of the HVAC considerably for ICF and have a very well insulated house.

celluose does not have air sealing abilities. Sound deadening, yes, but not air sealing. The only insulation product that seals air is open and closed.
Your are certainly right on track with the 2" exterior foam though, good move. After you get an EXTERIOR AIR BARRIER set in place (I highly recommend making your air barrier plane the sheathing plane and not the foam plane) then you can fill the stud bays with whatever you want and it will perform much better (or actually close to manufactors claims rather).
Steps to put your money:

Air seal first. walls, floors, ceilings, even basement slab if you have. Your house as 6 sides.

Insulate- it will pay you back, and its cheap to increase. You have the labor to get it there to begin with, adding a few more inches, especially in the attic, is min. dollars. Shoot for r55-60 in your attic as an example. I recommend blown fiberglass instead of cellulose for various reasons.

Thermal bridge elimination: You are already on this path. 2" of XPS is a great move. Caulk/tape your sheathing plane, then tape your XPS foam. Provide a furring drainage plane and you are good to go.

Window and door selection and design: solar design should be taken into acount, correct glass tuning. Consider using triple pane glazing, but probably hold off on that upgrade as one of the last things, if at all. A good dual pane hitting aroudn u .28 in your claim will do pretty well. Look at fiberglass products.

NOW you can start to upgrade your HVAC. The above items are not moving, minimal to no maintanence things for your house. Hvac systems are expensive (as you know!), need serviced, and can break down. They can also be reduced by the above items. For example, my home is 3600 sqft total conditioned in cold zone 6 with 7800 HDD. My home only calls for about a 2ton system to heat it.

check out my blog for more information, pictures, and additional tips along with nerdy reasons for the madness.

Here is a link that might be useful: home building blog

celluose does not have air sealing abilities

Dense pack cellulose does not eliminate the need for an air barrier material in new construction, but it can be so tight in retrofit as part of the air barrier assembly that it "comes pretty close", according to Dr. Lstiburek of Building Science Corp. based on the results of extensive testing. Incidentally, you can get the same air sealing benefits from dense pack fiberglass.

What is often confused is that you don't just have one air barrier in a well-built home, but several. It's not as if you seal the exterior and say the rest doesn't count.

Great comments. Would like to reiterate the air-sealing goals of the project. What is your blower door test target? The blower door test results usually have a bigger impact on energy efficiency than insulation options.

Good results usually come from well sealed sheathing, but more importantly; transitions (concrete to bottom sill plate, top plate to roof etc). The air-sealing effects of cavity insulation is practically mute in comparison.

ICFs are rarely a cost-effective path to energy efficiency. Most ICFs barely meet the new minimum energy codes. I would recommend pre-cast concrete panels and SIPS way before ICFs in most situations.

You have to remember the heating system is not up for discussing, that IS what is going in. The home will be also a bit of a showroom because we sell so many ground source heat pumps(we are on track for 40+ systems this year) I want to have a home that I can bring people to show how they work. The 7 Series is the highest efficiency system and most comfortable forced air system in my opinion on the market. They only come in 3, 4 and 5 ton sizes but since they are a full variable capacity they are up to a 5.3 COP and 41 EER at 50% of capacity.

So HVAC aside I am mostly just asking, what others are doing to get their numbers low in the first place. I have been hearing conflicting information on the cellulose. Many say it air seals pretty well when damp applied and nobody in this thread has mentioned damp applied cellulose, everybody seems to be talking about blown in which is a different process and different result unless I am mistaken somehow. I have heard the damp/wet applied cellulose is not as air sealed as foam but close to it and if I add the foam outside with tape it should be about the same but with a recycled product, with higher fire retardant and sound deadening.

In my post I mentioned that cellulose slows air flow.
this comment was to address your post of wet blown
cellulose, sorry I didn't specify.

with foam sheathing on exterior, any conventional
insulation inside wall stud bays and ADA. you'll
have a tight, thermally broken wall.
I wouldn't go as far as to compare wet blown
cellulose to foam spray insulation, as my testing
shows that there isn't a comparism.

if you tape the seams of the foam sheathing,
and seal any holes before cladding is installed
then you'll be good. sealing the sole plates to
slab/subfloor is also necessary, or you'll have
infiltration the length of every exterior wall.

next comes the holes we cut into our walls...
windows and doors. proper flashing on exterior
and low expansion foam to interior makes these
openings tight. be ready to educate yourself on
proper flashing. each window mfg includes directions
for this on each window..usually these directions are
left on the window & builder installs the way he/she
always has. so take the time to read & understand how
to keep water & air out of these opeings.

once you foam sheath the walls, insulate, ADA ,
seal sole plates, flash & seal window/door openings
your next and most important area to air seal is the
ceiling between living and attic space.
tough enough on a one story house...but if house
is story & a half or two story..you need to pay a lot
more attention to air sealing.

on the attic floor/celing of living space we make a lot
of holes. electrial/lighting, bath fans, supply & return for
hvac & stove venting. recessed lights are a huge air
infiltration site when IC (insulation contact) and not
ICAT (ins contact air tight) recessed lights are used.

knowing what you plan to use in attic...configuration
of house, location of equipement & ducts all factor in on
the insulation type of attic.
knowing those details will help us to advise you as
to your choices.

you are on the right track with foam sheathing walls...
but details are important..as most loss
is from attic..focus on this area is very important.
sun hits one wall at a time...but the roof gets
sun all day.

best of luck.

Brian, I think you need to educate yourself about ICF.

I perfer SIP's but that is my prefrence.

OP won't gain anything
but structrual strength from changing from
a better built wall (aka perfect wall as per building
science) to the more expensive ICF.

btw, just got this link in an email yesterday.
as this is the type of foam sheating I've recommended
in my hot humid climate...this link shows why
NOT to use this product in cold climates.
just fyi OP
http://www.buildingscience.com/documents/information-sheets/info-502-temperature-dependent-r-value/

excerpts:
Some insulation materials exhibit better thermal performance as temperatures get colder (i.e. the apparent R-value increases as the temperature decreases) and some materials exhibit worse thermal performance as temperature gets colder (i.e., the apparent R-value decreases as the temperature decreases). The latter is the case with polyisocyanurate products. Material properties vary from manufacturer to manufacturer.

and:

Implications
For cold service temperatures the following recommendations are offered:
âÂÂ
Use thicker layers of polyisocyanurate insulation to ensure that the performance meets expectations. NRCAâÂÂs most recent recommendations are to assume that polyisocyanurate has R-5.6 / in. when designing for warm climates and R-5.0 / in. when designing for cold climates.11

âÂÂ
Use a hybrid insulation approach ��" install cold temperature-tolerant insulation over top of the polyisocyanurate insulation to increase the mean temperature of the polyisocyanurate.

BSC continues research into the temperature dependency of different insulation materials and products. Future publications will address exterior insulating sheathing products for residential and commercial wall systems.

best of luck OP

It still seems OP is concentrating on the air infiltration characterisitics of the cavity insulation which is wasted effort for the most part. I agree with EnergyRater's comments and would add that between the window frames and framing is a place we see measurable infiltration despite being meticulous with canned spray foam to stop it there. We are currently using a combination of backing rod, caulk, tape and spray foam to improve this vulnerable location.

Iam no expert in ICFs but do consider myself well educated with their benefits and drawbacks. According to Oak Ridge National Labs, ICFs generally have an effective R value of 12. This doesnt meet minimum energy codes (worst performance allowed by law) for much of the country. Reward has a new slip in panel that boosts Rvalue but you have to increase the wall thicknesses to painful levels to allow for more concrete.

ICFs are fairly airtight in the wall areas, but not more so than well sealed sheathing. Many ICF homes have considerably higher air infiltration which is probably due to the increased difficulty of air sealing wall to ceiling/roof transitions and irregular window framing.

Traditional formed concrete walls with exterior foam sheathing will perform better than ICFs as the Thermal Mass is completely inside the building envelope. Labor costs are a big factor with ICFs and one of the many reasons I usually prefer pre-cast concrete panels in below grade applications. In Southern parts of the US where the relatively low R-value isnt a big deal, termite vulnerability is the major issue.

a friend of mine just insulated his attic with some white stuff that he was all proud of. he took my husband up to his "igloo attic"

i was in the kitchen with the ladies, so didn't check it out.

he's a genius, literally, so i'm guessing he made an informed decision when he chose this white foam stuff for his attic.

just throwing this out there