Often times, bedrooms closest to the garage or bonus rooms above the garage get the hottest during a summer in Phoenix, AZ... and for good reason. Usually, the garage is hot and remains hotter than the outside, even well into the night. All that heat built up during the day takes time to dissipate, and a lot of it gets transferred into the home, causing adjacent rooms to heat up more than the rest of the house.  

Here is how you can check if there is insulation present in the walls from the house to the garage. (Please note, our outside garage walls are never insulated because this is technically unconditioned space).

1. For safety, turn off the electricity at the breaker to the garage and adjacent rooms' outlets.
2. Take a flat head screw driver and unscrew an electrical outlet that is on the wall in question.
3. Use a paper clip, drill bit or screw driver and push it in between the blue electrical box and the drywall gap.
4. If there is insulation, you will feel a bouncy resistance when you push in... that is your fiberglass batt insulation! If you feel nothing, you may not have any and I suggest drilling a hole in between the studs and performing the check again to verify.
5. You may also be able to see in the drywall gap with a flashlight and visually see the insulation, it will be either pink fiberglass batts or a white color.
6. If you don't have any outlets, you can drill a small hole with a drill bit in a hidden spot in the wall and perform the same check.

Surprisingly though, as a Phoenix energy auditor, this is not the sole cause of those adjacent rooms getting warmer than the rest of the house in the summer. In fact, in more than the 1,000 home energy audits we have done, 100% of the rooms adjacent to the garage walls and ceiling were insulated. Now were they insulated properly? Possibly... but still, don't get hung up on the wall insulation.  

After performing an energy audit, we have been able to diagnose and correct the cause of the rooms heating up and it is attributed to three things in order of the most common causes.

1. Poor airflow
2. How the insulation was installed in the attic
3. Leaks from the duct work