When I purchased my 1952 Cape Cod–style house in 2018, I was well aware of how much work it would take to improve the energy-efficiency and overall performance. The house had most of its original asbestos-concrete siding, there were signs of past water damage, and there were the normal problems that come with a Cape house because the attic knee walls are both inside and outside the air control layer.

The natural gas–fueled forced-air system (heating only) was nearing the end of its life and eventually failed; there was also a natural-gas fireplace in the living room. The electric water heater tank was installed in 1990, and is still operating today, although I have replaced one element and the thermostat.

There was something happening on the north side. I knew it wasn’t an active bulk water leak from the roof, which had recently been replaced, but I was pretty sure there was some water intrusion through the walls and probably a lot of air leakage that could be causing some condensation issues in both the roof and walls. I suspected there were also ice dam issues, which were confirmed the first winter.

Collecting data to help prioritize

I purchased the house too late to perform any exterior projects the first year, so I spent the winter building an office in the basement and learning about how the house performed under existing conditions.

I had conducted a blower door test before buying, and had been expecting results in the high single digits, maybe 8 or 9 ACH50. It was a little leakier than I thought at 12.3 ACH50.

The leakage area at 10 Pascals (Pa)—what might be expected during the winter months—was equivalent to a 12-in. by 24-in. hole in the building enclosure. This is not something you want when you live in Climate…