Almost all of the work I perform is on houses that predate the Civil War. As I’ve written about here before, doing the right thing by them in terms of insulation isn’t always straightforward. In fact, doing the right thing on any kind of energy retrofit of an existing house almost always means navigating some trade-offs.
The lid is usually relatively easy. You head into the attic and either spray foam the hell out of the roof, or you air seal the attic floor and then blow in a couple of feet of cellulose. Of course, it’s a little more complicated than that, but these energy improvements don’t require gutting exterior walls and figuring out how to air seal and insulate a wall assembly that probably doesn’t even have sheathing.
What if I were to tell you there’s an easier way?
Insulate the outside
Forty years ago, in 1981, the same year that Fine Homebuilding magazine came out, a Canadian fellow named John Larsen came up with a way to insulate houses from the outside. Larsen wasn’t just Canadian, he was from Edmonton, Alberta—a city that can claim the harshest winters south of the Arctic Ocean. The man was solving a real problem.
Larsen built simple trusses that he nailed to the outside of the house to provide added depth for insulation. His original design joined 2x2s together with 8-in.-wide strips of ½-in. plywood glued or nailed into dadoes. He would nail these to the house’s studs over the wall sheathing, completely separating the insulation layer from the interior walls. This simplified the insulation installation process significantly, with no need to weave batts around pipes and wires.
The trusses ran down to the mudsill, allowing for simple insulation of the…