We’re rebuilding our detached garage with an in-law unit above it. Do I need to insulate the garage as well as the studio unit?
It will definitely be cost effective and more comfortable, so yes.
If you insulate the garage wall and ceiling and there is no heat in the garage, in the winter you will hold the cold in the garage. Insulating the garage ceiling with the in-law unit above will sound proof the floor/ceiling and if the walls and ceiling in the unit are insulated correctly the unit will hold the heat.
Your locality will require you to insulate the ceiling of the garage when you finish the room above.
Yes, you need to insulate the garage and the studio unit.
Yes, ceiling insulation and wall insulation area highly recommended in residential dwellings. Please consult with your contractor on what type of insulation is required. Plus, you want to make sure to do everything up to code and permitted by your city.
Whether you are building a new garage or renovating an existing garage with a in-law suite, do you need to insulate? The answer is yes, but not only to be more efficient on bills when the in-law suite has a temporary visitor or a long term resident. Local building codes require a certain r-value in both the ceiling and walls on the in-law suite and garage.
In my county an in-law suite above a garage is not even legal, but in some areas it is. Yes, you must insulate the ceiling of the garage. Also be sure to air seal as well. That means every wire through the topplate of the walls, the light fixtures, pipes, and anything else that penetrates the ceiling must be sealed. That is to prevent car exhaust from leaking into the living area. In some areas, an exhaust fan hooked to a carbon monoxide detector is also required. Definitely a good idea anywhere.
I would definitely insulate the garage ceiling.