Trying to get the most out of a government building that is unfortunately "required" (don't ask) to be CMU (no other option) and insulated with foam. Location - Utah County, Utah. I was able to talk the architect into switching from EPS to Polyiso, but then the question arises - foil or fiber faced? I was able to convince them of going from 2 inch to 3 inch. Despite the temperature regularly being in the teens at night (like last night) and 100+ in the summer, some "high efficiency" decision makers are trying to just go with the minimum they can get a away with. But the argument now, is will foil faced foam introduce vapor issues because it is not actually thick enough? Originally, I tried to make the case for ICF, but that fell on deaf ears. Anyway that's my question - based on what i have to deal with, CMU and 3" of foam and a brick exterior. Which is the better option for our climate?

I forgot to mention 8" fully grouted block w/rebar and a liquid applied "air/moisture barrier" on the exterior of the block. 1" air gap between foam and brick.

For a brick clad CMU building with minimal or no roof overhangs foil-faced would be preferred, but not absolutely necessary. Don't rest the cut edges on masonry or concrete since it can (slowly) wick moisture if you do.

Foil facers are typically <0.05 perms, independently of the thickness of the foam.

Expect the masons to complain about the longer brick ties needed for 3" foam, and don't let them talk you into skipping the air gap between the foam & brick cladding!