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Exterior insulation zone 3a – GreenBuildingAdvisor
Yep, sounds like a great assembly. R-20 CI in just about any climate is pretty much the cat’s pajamas. As Antonio mentioned, detailing and execution are the important parts.
Randy Williams just wrote a great article on the perfect wall:
https://www.greenbuildingadvisor.com/article/a-practical-perfect-wall
The Oak Ridge Building Science Advisor Tool is also a nice resource:
On the advice side: If possible, during the rough-in stage, I like to do extra visual QC and run a handful of pre-drywall blower door tests to ensure my envelope is performing as designed. At a minimum I do one post dry-in, and another after MEP rough-in is done. The caveat is that your envelope can’t be connected to any vented spaces (i.e. if you have a vented roof and don’t hang your ceiling drywall or have an air-tight membrane in place on the ceiling, the BD test is useless.)
And with no drying potential to the exterior, a good HVAC-DeHu strategy is also needed.
Good luck!