Last year I built my first new house, with my wife, the help of some friends, and a few hired subs. Our air-sealing goal was 1ACH50 and we gave that number to the engineer who did our energy model. Knowing that we’d be sizing our minisplit based on the results of his manual J, I became obsessed with making sure the house would perform as predicted by the model.
Having worked at FHB and GBA for a couple of decades and having completed an energy retrofit on an older home, I felt pretty confident in how to plan for a continuous air barrier. Having little hands-on experience with new homes, I wasn’t going to leave anything to chance. Everywhere I could, I used a redundant, belt-and-suspenders approach to air-sealing. For example, I air-sealed beneath the mudsill, applied a bead of sealant between the outside face of the mudsill and sheathing, and sealed the whole area again when I installed EPS rigid foam cut-and-cobble style at the rim joist. I also used an expensive approach to air-sealing the ceiling (similar to this) that I felt more confident in my ability to do well than using the airtight drywall approach, or a membrane.
After a series of blower-door tests at two stages of the build, we averaged about .5ACH50. I was thrilled with the results, but I can’t say our approach was cost-effective. Belt-and-suspenders air-sealing means two materials where one could do the job, and though it has other benefits, our ceiling detail included a whole bunch of lumber and sheathing that could have instead been a couple rolls of a membrane, or just some sealant to make the drywall airtight.
Shortly after moving into our house, I attended a meeting with a group of very experienced local builders.…
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