Building Science Puzzle: The Wrinkly Shingles, Part 2 – GreenBuildingAdvisor

By Randy Williams | July 24, 2025

This is the second post of GBA’s new series, “Building Science Puzzles.” The first post, which you can read here, discussed the reasons for the investigation, explained the process, and shared the observations, data, and other findings that were collected. This second post, published a week after the first, details the answer, or at least a hypothesis about what is going on. There may be additional clues to the puzzle in the comments section of the first post.

The Case of the Wrinkly Shingles

There’s a lot going on in this investigation. We have buckled shingles in half a dozen spots across the peak of the roof, which—according to the homeowner—appeared several months after they were installed.

We have an attic truss design, which suffers from the same issues as a Cape Cod home. It’s hard to insulate correctly and difficult to achieve proper attic ventilation when a vented roof is the desired assembly.

There is some evidence of moisture damage at the peak of four of the attic trusses. This is an issue I’ve been diagnosing with regular frequency in my climate. I’ve even written on the topic here on GBA. Are these three conditions connected?

Wrinkled shingles

Let’s start with the wrinkled or buckled shingles. This is a problem I see from time to time with new construction. I’ve discovered a few causes for the condition. Before we get there, I’ll comment with something that should be obvious. Asphalt shingles are very stable; they expand and contract very little with temperature swings or moisture.

Uneven roof sheathing. A flat shingle is going to follow the contour of the roof. If a roof has a hump or belly, then the shingle will follow the contour. If there is a…