Flashing Failure & Perimeter Leaking
The most common cause of skylight leaks — by a significant margin. Step flashing, counter-flashing, and the curb apron around the skylight perimeter fail before the glass does. When flashing separates or corrodes, water follows the frame into the ceiling cavity without touching the glazing. A correct diagnosis determines whether the glass or the flashing is the entry point before any repair is attempted.