Value of significant insulation for a garage
I’m in Zone 5 (Colorado Springs, Co) and in the process of designing a carriage house (2 car garage below an apartment). General plan is to do 2×6 on 24″ centers, blown in cellulose, air barrier external to sheathing, then exterior rigid insulation sufficiently thick for my climate zone.
Where things get more complicated is when looking at the garage level. It does not appear that there are very good garage doors both in terms of thermal bridging/insulation and very good sealing around the doors. That being the case, does it make sense to go to pretty good house levels of insulation on the garage level? The garage ceiling will need a good air barrier to keep garage air from going into the apartment anyway (tentatively thinking of a couple of inches of spray foam on the ceiling coupled with careful air sealing/construction). Prior to realizing the achilles heal that is the garage door, I had been planning on rigid insulation for the entire exterior of the structure, insulated slabs and footers. I’m considering doing some modelling to put some numbers to this but guessing some folks have already looked at this, does it make sense to do more than standard insulation (cellulose studbays, air sealed exterior) on the garage level?