Garage roof insulation is not always necessary. But in some cases it can be a beneficial or even needed upgrade to put insulation in the roof of your garage.
Living space above the garage
If you have any living space above your garage, the garage itself needs to be insulated in order to make the space above it comfortable. Both the walls and the ceiling of the garage are recommended to have insulation installed.
If there is an attic that is above the garage that you don’t use as living space, the most cost-effective option would be to have blown-in cellulose insulation put in the attic.
Garage workshops
Another reason you might want to consider insulating all walls of your garage is if you use it for a workshop. If you spend a lot of time in your garage it makes sense to insulate it. The temperatures in garages can be extreme, and insulation will help *even out* the temperature. If you do plan on using your garage as a workshop, make sure to not only insulate your ceiling, but the walls as well.