We put lots of insulation in the attic, less in the floors and least in the walls. There’s got to be a good reason for that, right? It’s got to be because the attic loses the most heat, right? Wrong!
“Well, it must be because heat rises.” Wrong again
You’ve heard it said and probably said it yourself that heat rises. It does not. Let me say it again, heat does not rise. When air is heated it become less dense and heated air will float up over colder air.
The fact is that heat tries to move in all direction equally. Heat doesn’t care about up or down. It wants to go through your floors and walls the same as it does the ceiling.
So there must be a good reason we don’t insulate walls and floors as well as ceilings, right? Yes, but the reason has nothing to do with how heat escapes. We put less insulation in walls and floors because it’s harder to get insulation in a wall or floor than it is to cram it into an attic. We would gain nearly the same reduction in heat loss by insulating the walls and floors to R-49 as we do the ceiling.
So why don’t we change the way we build walls and floors so we can insulate them better? We simply don’t like to change. We want to keep building the way we learned 25 years ago because we know how to do that and it’s easier than learning new methods. It’s also cheaper to build thinner walls and floors.
But what if the energy code requires us to build more energy efficient homes, will it pay to change the way we insulate walls and floors, or should we just try to cram more insulation in the attic?
There is a point of diminishing returns by increasing the thickness of insulation. As the energy code changes we will need to look at the way we build and consider making our walls and floors more efficient. It doesn’t have to be radically difficult.
Building with framing 24 inches on center and reducing unnecessary wood in the walls will improve efficiency. Installing a layer of foam insulation on the outside can significantly improve efficiency. Using wider studs or a double 2 x 4 stud wall with the studs offset allows room for extra insulation. Spray foam insulation not only insulates better, but also reduces air infiltration.
It doesn’t have to be difficult to insulate walls and floors better, it just needs to be different.