A comfortable, energy-efficient home begins with a good building enclosure. That means control layers. You’ve got to control the flows of moisture, air, and heat.
Today, let’s talk about controlling heat and further. Let’s focus on heat going through the top of the house. If you’ve read my Flat or Lumpy article, you know it’s better to have a uniform coverage of insulation rather than a lot of insulation in some places and little insulation in others. But you may not know about one place where many homes just can’t get enough insulation.
Yep. I’m talking about the space over the exterior walls, where the roof comes down and leaves little space for insulation. Take a look at the Image #2 below. It’s from the Building America page on minimum insulation at the attic eave.
The trusses seem to be made from 2x4s, so there’s about 4 inches of space for insulation over the exterior wall (at the bottom of the photo). The rest of the attic will have about 12 inches or more of blown insulation. Hmmmm. Is there some reason that the space over the exterior wall might have lower susceptibility to heat loss and heat gain? In summer, it could be a bit cooler there because of venting (not shown). In winter, that spot is likely to be worse than the middle of the attic, again because of venting. Overall, though, there’s not good reason to have less insulation there.
And speaking of venting, check out Image #3, a Building America photo showing incorrect installation of the baffles. The problem there is that the cardboard baffles are stapled to the inside of the top plate. In this house, as a result, there’s going to be absolutely no insulation directly…