I inspect the skylights during a home inspection.
A leaking skylight is a common experience for homeowners. It’s essentially a piece of glass covering a hole in the roof. From outside, home inspectors can look at the glazing (the glass) for cracks or breaks, loosening of the flashing, and rusting or decaying frames.
The flashing installed around a skylight is similar to the flashing installed at a chimney stack and at a roof-to-wall intersection. The inspector should look for step and counter flashing. Skylights should also be inspected from the interior.
Look for watermarks and streaks coming from the skylight. Don’t confuse condensation marks with roof leaks. If the skylight opens, the inspector could open, close, unlock, and lock the skylight.
An operable skylight could be used as a vantage point to observe the roof covering. Homeowners should not be surprised if their skylight develops a leak.