ah, I realize now that the blocks are where they nail the siding into ... so they have more to bite into than just the plywood.

What about hot water heater.. tankless ?

I don't know about a heat pump HWH... ours is fine, but it's noisy and big. It's in a large unfinished heated basement so it works OK. Space is tight here.

Our water is mildly hard but not super hard.

So after this week I decided I Want to heat the garage, however we will still put proper insulation in between garage ceiling and apartment floor upstairs.

If I insulate the garage portion and heat to ~38 or 40F, can I use plywood as the interior wall and Roxul insulation? Or do I need to use drywall and do we need a vapor barrier?

Basically, no matter what you do regarding insulation and finishing, code is going to require that you put up a vapor barrier and drywall. Fire and fume protection.

Is that also the case for the garage walls? I know it is true for garage to apartment ceiling...

Back to the garage and apartment - getting almost time to decide on insulation.

Have seen opinions range but most people around here are in the "just spray it" camp.

I am wondering about doing roxul in the walls and spray the ceilings plus spray any spots that are hard to get with roxul batts?

Will mixing and matching cause any issues?