A garage wall is still an exterior wall.
And, as such, if it abuts the house, it needs to be insulated! Remember the 5% Rule!
On a new construction inspection I noticed something interesting. The room adjoining the kitchen and garage was very warm.
The area in this photo is in the garage attic space. It is above the garage ceiling, but still abuts the house.
It opens to the entry from the garage, which is also a combination mud room and laundry room.
Entering that space from the kitchen I noticed it was kind of warm.
It had its own floor register and was serviced with HVAC, but that wasn't working.
So the question is why would that space be warmer?
That is what prompted the view in the garage attic space.
The thermal image here clearly shows what happens when the wall from the garage to the house is not insulated.
But there is a second culprit.
A small attic space above the laundry room also has its own entrance, which is similarly experiencing heat.
What we have is a large area at the edge of a room that is poorly insulated.
That brings us to the 5% rule. Many insulation studies have shown that if 5% of a given space - a wall, a ceiling, or floor - is poorly insulated, or is missing insulation, that 5% will bring down the R-value of that space as much as 50%.
I have written a blog on this study which can be read here.
Looking at the wall and ceiling near the door to the garage it is evident that insulation is missing, or poorly applied, in the walls and ceiling. The attic access hatch also needs to be insulated. In my opinion the best way to insulate that is Styrofoam. A later of 3" of Styrofoam provides about R-15 and weighs nothing. Glued to the drywall of the access hatch it is a permanent insulator.
My recommendation: if rooms feel warm or cool there is a reason. The reason is insulation! Certainly the naked eye can inspect the insulation to see how well it is applied, but if access is difficult and that is not possible the absolute best way is with a thermal camera! And the 5% Rule always applies. It doesn't take much poorly-installed insulation to affect the comfort of a room!