Yes, I'm aware of that...I worked to help manage an insulation contracting company for a few years in my past. But this is a workshop, not a residence. The block walls already provide some minimal level of "insulation" due to the air spaces and the majority of comfort factors will be remedies by doing the ceiling properly. 2x4 walls would also reduce the shop space...not a huge amount, but still there...and raise the cost of construction. That may not be warranted with the block walls already there. My MiniSpit easily handles the shop year-round with minimal cost with the way I constructed things. I would, of course, do things "beyond code" (as we did for our major home addition) for a residence.