Everything is sort of bad, but at least one thing is awful

I have two mental models for understanding and improving building performance. The first I call “Everything Is Sort of Bad.” It says a building is pretty bad (but not horrible) almost everywhere, in most of its systems: the thermal boundary, the pressure boundary, the ducts, the water-resistive barrier, and so on.

The second I call “Everything Is Sort of Bad, but at Least One Thing Is Awful.”

The first model is helpful. There are lots of places in a building where slight improvements yield large benefits. Attic air sealing is usually a good example. Cracks at the drywall ceiling tend to be fairly uniform, yet plugging all the holes in an attic yields a significant improvement, usually a 20 to 30 percent overall leakage reduction, or at least two thirds of the potential improvement on one of our projects. Here, geeky diagnostic tools are genuinely helpful: blower doors and duct blasters are great for verifying the effect of these measures.

But it’s often hard to tell whether the marginal improvement left hard-to-find problems behind. A 35 percent leakage reduction is great, but it doesn’t tell us whether the cantilevered second-floor joists, reachable only from a small roof over the garage, were sealed.

The second model includes all the lessons of the first, but tells us to be on the lookout for egregious problems. And when you’re looking for isolated but big problems, it’s unfortunate, but you may have to actually listen to the people who live in the building.

Originally published on the Tay River blog. Lightly edited.