I have a home office, which has 2.5 walls that border the outside of the house, and a floor that is over the garage. It's a nasty combination. It gets quite hot during the part of the day where the sun shines on one of the outside walls. The room is easily 5 degrees warmer or more than the rest of the house.

I can feel it, too. The floor itself is warmer than the floor inside the rest of the second story. The walls that border the outside are noticeably warmer to the touch than the other walls.

This house was built in 2006, so it's relatively new construction. And yet I question whether it was insulated correctly. Once we added a ceiling fan and had to open up the wall above the light switch -- there was no insulation there. That part of the wall does not border the outside, but that same wall DOES on the other side of the room.

I found this which is helpful for determining if there is insulation:
Determining if there is insulation behind a wall

So my question is really two things:

  1. If the wall behind my switch is not insulated, does that mean they probably didn't insulate the entire wall? Is it common to only insulate the part of a wall that borders outside and not the rest?

  2. Are there any DIY techniques to insulate the walls further that are relatively cheap and easy? If it does have to involve tearing open the walls, how big of a deal is it? What kind of cost would you think for a room that's about the size of a typical modern house's extra bedroom?


For Q#1, no. It is typical, indeed expected, that they will only insulate the parts of a wall that border the outside of the home. Insulation isn't that cheap.

For Q#2, get an IR/no contact thermometer, frequently selling for $20 online for the lower end models. Check all the walls in the room and compare to other walls on the same side of the house. This will give you an idea of whether the problem is real or imagined.

The reason I suggest the issue could be imagined is that people, lights, and electronic equipment put off a lot of heat, possibly more than you are seeing transmitted through the walls. Just by working in the room, you will likely see a large spike in temperature.

The easy fixes for this problem are more weather stripping around leaking windows, outlets, etc and adding insulation to places you can reach, such as the attic. And finally, make sure your air vents are properly adjusted to send more air to the rooms you use. You may consider placing a fan on the floor at the door blowing cool air into the room (effectively pushing hot air out the top of the doorway).

  • Thanks. I do know it's not imagined, because the room was unoccupied for several months when we first moved in. Even completely empty with no lights on (door open), I noticed the room was always really hot compared to the rest of the house. But good point, my computer and mere presence probably doesn't help! Oh, and interestingly, there's no other equivalent wall to test with. The other similarly facing walls in other rooms are shaded by our neighbors house. This room is weird because it sticks out a little. Jun 22 '11 at 1:24
  • 1
    If the garage is cooking you on the warm days, you may want to look at installing some exhaust vents or cracking the door open to get some of the heat out. If the floor isn't insulated, fixing that via the garage ceiling will be relatively easy since a messy garage isn't that big a deal. Just remember, paper side of insulation goes towards the living space.
    – BMitch
    Jun 22 '11 at 1:39

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