Short Answer
Potential causes include failed flashing, deteriorated sealants, improper installation, damaged skylight, and surrounding roof deterioration.
Detailed Explanation
Skylights are large penetrations through the roof surface, making them inherently vulnerable to water intrusion. The most common causes of skylight leaks include: flashing that has failed, deteriorated, or was improperly installed; sealants around the skylight frame that have cracked or shrunk with age; improper installation of the skylight or its flashing; physical damage to the skylight itself (cracked glass, damaged frame); and deterioration of the surrounding roofing materials. Because skylights are at the roof surface, they're exposed to the full force of rain, wind, snow, and ice. Proper flashing and installation are critical — a skylight that's poorly installed will leak regardless of the quality of the skylight itself.
Why It Matters
Skylight leaks are common and can cause significant interior damage. Proper diagnosis identifies whether the skylight, the flashing, or the surrounding roofing is the problem.
When Repair Makes Sense
The leak is caused by failed sealant or flashing that can be replaced without removing the skylight.
When Replacement Makes Sense
The skylight itself is damaged, the flashing can't be properly replaced in place, or the skylight is old and reaching end of life.