Adding rigid insulation to the exterior of your house is using a system called EIFS (Exterior Insulated Finish System). The industry has improved its technology since the early systems industry encountered many very serious problems of moisture infiltration behind the rigid insulation, deterioration of sheatingn, and mold growth towards the interior living space. Installers of such systems need to be qualified and insured for providing installation services. You may also want to check with your home insurance company if such a system impacts your premium.

With the new National Energy Code, your home is required to have a certain R-value in the walls, roof, foundation construction of your home. You can achieve this with traditional construction of various insulation products in your wall cavities. It's nothing more than framing with 2x6s or deeper studs and using any option of insulation product (i.e. closed cell expanded foam insulation, cellulose, batts, etc.).

Using the insulation within your wall cavity and other updated construction industry standards will allow you to use most any exterior finishing products (fiber cement siding, wood siding, masonry or stove veneer, etc.).

With any exterior wall finish, your architect will need to detail the rainscreen underneath, and your builder will need to be knowledgable of correct construction industry standards.

I myself stay away from EIFS projects, too much liability, especially when the builder believes that budget dictates the cheapest unqualified installer trumps qualified installer. Not worth the risk.

You can do your own extended research by just googling EIFS. Pay attention to parts of the country where building departments have instituted "No EIFS Ordinances.

In order to achieve the required r values per the latest energy code, rigid foam can be used with great success without the EIFS system described above. The issues are typically flashing it properly and taking account the added thickness with respect to trim details, window and door reveals, etc. one of the best ways to tightly insulate a home is with a "flash" coat of closed cell spray foam with the rest of the wall cavity filled with traditional fiberglass or cellulose insulation. It is a great cost effective alternative to an expensive full spray foam insulation or to the awkward detailing of exterior rigid foam.

What would be the benefit of this flash coat?

If its just for making things air tight against the outside wall can't you just caulk the seams of your sheeting and do plain batts?

Sorry I meant sheathing joints.

The flash coat seals the building envelope due to the lack of permeability of the closed cell foam. While the caulking of the sheathing joints would help, it does not address the permeability of the sheathing itself. The closed cell foam will address this issue. If you google "flash and batt system" it will give you a lot of information. The biggest factor is the thickness of the foam for your climate to prevent moisture condensation within the wall cavity.

Ok that makes sense. Thanks for the quick replies.

No problem...any other questions just ask away.