Currently the detached garage walls are insulated with batts of insulation, however the ceiling is not, so here in Illinois, the garage is pretty much unusable most days in the winter. I use this garage as a woodworking shop.
The obvious approach would be to drywall the ceiling and just add more batts between the joists. However, the joists are spaced at 32", so Id have to install more joists if I wanted to drywall as well moving electrical that has been installed on the surface of the joists, so that option is last.
Another approach that would be cheap is to just staple down rigid foam boards on top of the joists.
Additionally, the roof does have 2 vents.
All in all, is there a better approach that wouldn't require drywalling?