Dana1-Thanks so much for your thoughtful explanation. This gives me piece of mind that OSB should perform fine in my wall stackup. At this point I plan to use Energy heel trusses with fluff cellulose attic insulation. Per your recommendations I think cellulose is going to give me the most bang for my buck. Return on investment for spray foam seems marginal when compared to wet pack cellulose. As far as attaching the foam board to the OSB walls, I plan to use spray aheasive to reduce nail penetrations. Probably will still have 4 penetrations per foam board to ensure board stays in place should the adheasive fail. On the fence about taping the OSB, but you seem to stress the importance. What is the most streamlined process for this? A small roller, brush, or spray paint primer? As far as taping the foam I know you recommended FSK tape. Is that going to be better than housewrap tape? No difference? In gable areas that are not living space I planned to just install vinyl siding directly to the OSB with no water barrier. Do you approve? And in garage area looking to the fanfold foam for vapor barrier under brick. I suppose alternativly I could go with tar paper.

Another option to taping the foam board seams is to use two layers of 1" foam board with staggered or off-set seams rather than one layer of 2" foam board.  

Still another option to taping the seams on the foam board or OSB  is to paint the seams (2 coats) with an elastomeric paint or roof coating such as Black Jack Ultra Roof 1000.

Here is the link for the Black Jack product or you can google [elastomeric paint] for more info and other options.

Black Jack Ultra Roof 1000

You can do a mile of primered seam 2" on either side with a paint- sprayer in the time that you could do 100' with a brush or roller.

FSK tape is purpose-specific for adhesion to metal foils. Sheathing/housewrap tape MIGHT work, but they usually only spec the adhesion on those to other things.  The latter are a lot cheaper, to be sure, but you only get one shot at doing this "right".

Some sort of housewrap or felt has to go between the vinyl siding & OSB to deflect the bulk-water incursions of wind-driven rain.  Vinyl is inherently back-ventilated and according to some, needs no rainscreen-gap (I'm warming up to that notion), so it'll dry quickly & fully from rain incursions, but that doesn't mean it won't need something to keep the splash off the wood. OSB doesn't wick it up as fast as plywood or plank, but it DOES wick liquid moisture, and will be damaged by repeated wetting.

Fan-fold XPS will be a far better air-barrier than asphalt felts, and has more consistent vapor diffusion characteristics.  Over OSB it'll be a better choice than felt, despite the long & successful history of using felt with plank & plywood siding.

On the paint spraying OSB seams, do I need a commercial spray unit or can I just use cheap 99cent cans of spray paint/primer to do the job? In regards to my 2" ISO is it safe to set the edge of it on the top of my concrete wall and run to roofline? Somewhat concerned about moisture forming ontop of poured concrete wall and wicking into the foil faced foam. Should I hold it up a little or somhow protect the edge sitting on the concrete?

It depends on how many miles of seams, but I s'pose you could do it with an acrylic primer in 99cent cans. If you're going to be doing a lot of the painting in around the house in a DIY fashion a high volume/low pressure paint (HVLP) paint gun with a mini-compressor (or even the cheap integrated compressor types) are worthwhile tools to own.

If you leave yourself a ~1/4" gap between the iso-edge and concrete, filling it with one-part spray foam does a dual function of providing the necessary capillary break, and air-seals the bottom edge of the iso. Ideally you'd be using a non-wicking sill-gasket under the studwall's sill plate wide enough to extend fully under the iso, but it's still worth foam-sealing that edge even if you do.

Dana1 - Not to beat a dead horse, but I found these tape options resonably priced and wondered your thoughts? I was thinking maybe the 1599B http://www.venturetape.com/pdfs/sellsheets/1599B_sellsheet.pdf tape for OSB seams and maybe foam if you approve, but if not on the foam too then maybe the 1581A http://www.venturetape.com/pdfs/sellsheets/1581A_sellsheet.pdf. There are just so many tape options out there and browsing the web you can find some good closeout deals if it is what you need or can use. Thoughts?

They look like they ought to work in these apps- the foil one for sure.

I thought they both looked like resonable options. With my wall stackup, the walls will have to dry to the inside, correct? With the Polyiso and taped OSB there would be no place for exterior drying, correct? As you stated before I should not concern myself with this due to my climate and the 2" foam, right? I do have concern about condinsation forming on foil foam and holding moisture against the OSB sheathing and causing an issue or getting too much condinsation in the wall that cannot get out.

I would think that the dew point would be inside the 2" thick Thermax thus there would not be any condensation between the Thermax and OSB.  And the taped seams should keep most of the rain from ever reaching the OSB.  If the OSB does absorb some moisture then cellulose in the walls should spread it out so it will dry to the interior.

Alton has it right- you only get condensation on surfaces that are below the dew point temp of the surrounding air.
The foil against the OSB will be at the same temperature as the OSB, and any condensation that occurs from interior air (which will happen only under the most-extreme temperature hours of any 25 year period) will be on the OSB, where it'd wicked away into the cellulose more rapidly than into the OSB itself.

And with a brick wythe & an inch or more of cavity rain isn't going to hit the foil, and condensation conditions from exterior vapor drives at the surface of the foil facing the cavity will be fleeting & inconsequential if/when they occur. (The foil has very little thermal mass and will rise to the dew point rapidly with condensation- it'll ever be actively wet with droplets, but may experience moments where it lightly fogs before rising to the average temp of the cavity.)

Dana1,

Should the word "ever" be changed to "never" in your last sentence?

... the "return" pinky is quicker than the eye!

Yes, make that a "never"! (Thanks!)