I agree with checking the local codes in your area...... different parts of the US and parts of Canada have different codes based on the weather, safety, and fire risks. Don't assume that where you are is reflective to other areas across the internet.
Things I would start to consider when making any garage finishing choices:
1) You change in temperature from outside to in (your weather and heating/cooling)
2) Local fire codes (for both inspection and/or insurance reasons)
3) Safety (undrywalled vapour barrier can be a fire hazard, even if fireproof insulation is behind it).
4) How far you want to go (drywall, taped and finished, painted, etc), or just insulation and vapour barrier (not a good idea for long).
5) Money and time spent in the garage (how long are you in there vs cost of your improvements; how much *** pain it is to insulate and bring up to a higher standard)
6) Are you finished everything that you want to put behind the walls (electrical, plumbing, etc etc.)?
7) Quality of finish. Will the vapour barried be tuck taped at all joints? Does it meet with tape to the ceiling vapour barrier, and acoustical sealant at the sill plate on the floor. These steps if not done can come to bite you in certain circumstances dependant on your garage environment vs the outside environment. One person may have zero problems, and the guy across the street may have problems in a comparable setup! Things like mould and air movement could pop up.
8) Heating/cooling unit (and cost of). With a less insulated space, you will likely need a larger heating unit.....
In Canada, we have vapour barrier everywhere there is insulation. Spray foam does not require a vapour barrier, and it is bad to put up any double vapour barriers where moisture can be trapped such as adding vapour barrier to spay foam.
The temperature changes are varied where I am. The low is expected to be -10 degrees Celsius (14 degrees fahrenheit) tonight in my area of Quinte West, Ontario (and snowing!).
The part that is imported to remember, where hot meets cold, there is moisture. If your house/garage is not wrapped or not properly wrapped on the outside, there is lots outside air movement (dirty insulation usually indicates this). An outside wrap around the house that allows NO air movement (2 layers of vapour barrier) is a bad thing, as it traps moisture.... so you need SOME air movement or ventilation, but not a lot. There are building wrap products out there that do this, but they are NOT a replacement for vapour barrier.
It makes sense to me, that the wider the temperature difference between inside and outside, the more moisture forms. So in Canada, or NY state, things will be different than Texas in the winter.
My current house is 1 year old. In my attached 21 X 26 garage, I have walls that have vapour barrier, insulated, drywalled walls next to any portion of the house that is part of the interior. The attic access is in the garage. This finishing of interior garage walls is likely due to fire codes. The house was wrapped with an exterior wrap that allows air movement, but keeps water from driving in from the outside of the house to the wood framing/sheeting.
The ceiling part of my house is insulated (blown in) and vapour barrier, and the garage ceiling is only vapour barrier and drywall with no blown in insulation..... likely to stop air movement and fumes from coming over to the house side. (and if I ever finish the garage completely, makes things easier to blow in).
In older homes in Canada, (having previously owned one built in the 1930's), there is often no insulation, insulation with a paper vapour barrier attached to the insulation, or insulation with no vapour barrier. Usually there is a big mix of it all if the house was modernized. One thing to consider with older homes, is the plaster walls, or old drywall walls have MANY layers of oil based paint and primer, that can act as sort of vapour barrier..... although it is debatable as to the effectiveness of that sort of vapour barrier.
Have a good day from the cold zone.....
R
