My Shed Stayed Dry in Normal Rain for Three Years. Then One Storm Told Me What I'd Missed.

The Hose Test

I kept the stream aimed at the same spot—low on the roof’s edge, where the rake trim meets the eave—and moved inside to watch.

The water wasn’t dripping from the ceiling or running down a rafter. It was appearing on the inside face of the wall, about six inches below the roofline, then trickling down to the floor in a dark line that soaked into the plywood.

That didn’t make sense. Shingles overlap, each course covering the one below by at least two inches. Underlayment—mine was fifteen-pound felt—sheds water down and out. The system is designed for gravity. Water shouldn’t be traveling upward or sideways behind anything.

I went back up and kept spraying, this time watching the outside while my phone sat inside on the mower seat, recording video. When I angled the hose to mimic wind pushing rain upward and sideways, hitting the rake edge at maybe forty-five degrees, I could see water hitting the trim, then just… disappearing.

Not rolling off. Not beading up. Vanishing behind something.

I turned off the hose and climbed down to take a closer look at the joint where the metal drip edge tucked under the shingles. The drip edge was white painted aluminum, the L-shaped kind you get in ten-foot sections at Lowe’s, and I’d installed it myself when I did the roof. It looked fine—straight, tight to the fascia, nailed every eight inches.

That’s when I finally saw it. Or rather, saw what wasn’t there.

There was a shadow line, thin as a credit card, running along the top of the rake trim where the metal sat. I ran my fingernail along it and felt it catch. A gap. Small enough that I’d missed it on every casual inspection, wide enough that pressurized water—pushed by wind—could slip right through.

Once I knew what I was looking for, I could see it on both sides of the shed.