How important is the attic to our heat and cooling bills?

I like this question, because it asks, why do I care, about something so tried and true.

If I stand in the middle of a room in my house, how much is ceiling? In a 12 x 12 room, the ceiling is 144 sq ft of area to be concerned about. If the ceiling is vaulted, it's even more.

In that room, each wall is 12 foot long, and let's say 9 feet tall. That wall is 108 square feet. If it's on the outside of the house we care, if it's on the inside, we don't. So how many walls are on the outside per room? In my house it's one or two per room typically. (Corner rooms are two.)

So if its one wall, it's 108 square feet -vs- 144 on the ceiling. If it's two, then its 216 vs 144 square feet of ceiling. No matter what, the ceiling is a big percentage of any room sitting under the attic.

Now, to be accurate, much of those exterior walls are penetrated by windows. Big chunks of square feet are actually glass. If you super insulated an exterior wall, but left a big single pane window in the middle of it...you will have missed the point.

But back to attics. In a single story home, all the rooms have ceilings touching the attic space. Simply put, a 3000 square foot home has about 3000 feet of ceiling touching the hot attic! A full two story would be about half that.

The most important reason to focus on attic is because we can actually do something about the problem pretty easily. Attics are accessible, the inside of your exterior walls aren't, (without serious deconstruction.) Blowing insulation, radiant barriers, and venting are all pretty easy, there are lots of contractors to choose from and it doesn't disrupt our lives...much.

Bottom Line - Attic is very important and easy to deal with.