We have a detached garage that's made of hollow clay bricks (structural terra cotta) covered in stucco, both inside and out. I'd like to insulate and heat it for use in the winter. The problem is that the terra cotta bricks are incredibly brittle and the stucco makes it difficult to see what I'm drilling into -- I'm wary of putting up framing to hold regular insulation batts. What can I use instead to insulate these walls? Can I just glue up 2" XPS panels (with batts in the rafters)?
We're in St. Paul, Minnesota, so the winters are cold and summers are hot. I plan to install a mini-split for heating and cooling; I don't need it to be warm in the winter, just tolerable, so I'm hoping to use the mini-split's minimum heat settings.
Here are some pictures to demonstrate what I'm working with. This is one of the three stuccoed walls:
This is the top of one of the walls, showing the top of the structural terra cotta:
And finally here's the interior of one of the terra cotta walls, where a previous owner removed some material (note that the brick behind the terra cotta block is a chimney, not part of the wall):
My plan so far is to glue up 2" foam board insulation over the stucco, then put mineral wool batts in the rafters. I'm hoping that plus a mini-split will get me through the first winter or two, and after the garage floor is replaced I can frame in some walls and add more insulation.