My house has a small room that was added on to the back of my attached garage. It's about 6 feet by 12 feet. There are two outside walls, one common wall to the house, and a common wall to the garage. When I moved in, I added R13 value insulation to three of the walls.
There's an HVAC vent on the interior wall and I also added a small electric strip heater, yet the room is constantly colder than the rest of the home. The insulation helped a bit, but not as much as I hoped. Any ideas?