LOL. It will be a s"comfy" as your house iis in summer with NO ac, and In winter with NO heat.

Buy a big portable air conditioner, and a portable heater. Plug in. Turn them off when not needed.

From a heating/cooling perspective having an insulated, detached garage with no HVAC simply means that temperature swings occur more slowly. For example, when it's hot out, the garage will heat up more slowly than if it wasn't insulated, but it will also hold in the accumulated heat longer.

If you want the garage to be reasonably comfortable at the times you want to it to be, it would make sense to insulate the walls and ceiling, AND to have at least some kind of basic HVAC...maybe a wall unit that doesn't have to connect to the rest of the house.

I" have a detached 3 car garage and I was wondering if it is worthwhile to insulate the walls and/or roof.""............................................................................

If the garage was designed by its architect to be partly habitable, that's one thing. But building a garage like that costs more, so most garages aren't meant to be living space. One of the consequences of this is that they're not usually sealed as well as living space.

I've found over the years that even when insulated, a garage takes significantly more BTU/hr to maintain at a comfortable temperature than a house. Also, unless you're going to keep it heated all the time, you need a large heater to bring it up to temperature fast when you want to use it. This tends to make garage heating more expensive than you first expect.

I haven't tried to cool a garage, but I imagine it will be pretty similar - big capacity needed. As with the heating, it's not just the initial cost, it's the operating cost (gas and/or electricity).

The bottom line is that you can certainly heat and/or cool a garage, but even with insulation, it's a possibly-expensive challenge to make it really comfortable. Aiming for maybe 55 degrees F in the winter and 85 F in the summer is somewhat more practical.

Still, as I said, it's not usually living space, which brings some code and safety questions into the picture.

I agree in the winter it will have to have some actual heating and since it is detached I really don’t see how that will be an enjoyable space in any season insulation or not . Really not built to be livable from what I understand