Three common errors exist which most often cause skylights to be blamed for leakage.
If a skylight is mounted properly and sealed to its curb per the manufacturer’s instructions, it is very unlikely that it will leak.
The first and most common is improper flashing around the skylight curb. To determine if a leak is the result of poor flashing, allow water to run down the roof from a point above the location of the skylight. Do not run water directly on the skylight itself. You will likely see
evidence of the leak appearing at this point and you didn’t even wet the skylight.
Secondly, a person unfamiliar with the design of the skylight may decide that the skylight itself is not properly sealed and apply caulking to the edges and integral weep holes. These are designed to allow condensation and moisture to weep to the outside of the building and sealing them will actually cause moisture to overflow to the interior.
Thirdly, a low-grade skylight design without a thermally broken frame in the wrong environment may condensate. This also may be interpreted as a leak. It is important to select the proper skylight properties for the application within any building.