We went out for a very early walk yesterday. The humidity was a bit high and the temperature was in the 20s, a clear day. I noted a grid-like pattern on several new houses as we walked. I took a picture of one, and you’ll find it below.
This is a very new well-built home employing conventional construction. What you are seeing on this south-facing exterior wall are patches of frost separated by vertical lines where the wall’s 2×6 studs lie behind the siding and sheathing. Warmth from the interior of the house is flowing through the continuous wood structure and melting the frost on the outside. Where insulation is placed in voids between the studs, less energy flows through, not enough to melt the frost. This is a really good demonstration of thermal bridging, (1) and why employing construction methods that reduce bridges (like the SIP walls on our Legacy House) can save a lot of energy.