Water dripping from a skylight during an autumn rainstorm looked like a minor leak. But when the roofer making repairs discovered an unexpectedly large area of saturated OSB sheathing and extremely corroded nails and plywood clips, he called me to take a look. We agreed that this was more than a flashing problem.

The roofer and I had worked on the house together 13 years earlier, when it was built. I was the framing contractor; the owners were the GCs. Vaulted ceilings were a key part of the home’s design, and I’d framed much of the 6/12-pitch roof with raised-heel scissor trusses. The owners then had the trusses insulated with open-cell Icynene spray...

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