How Does a Skylight Leak Start and Where Does It Enter?

Most skylight leaks originate from a failure in the watertight seal between the skylight unit and your roof. The flashing, which is the metal or rubber strip that wraps the skylight base, can crack, corrode, or pull away from the roof surface over time. This creates a direct path for water to seep underneath during rain or snowmelt.

Another frequent source is the skylight curb, the wooden frame that raises the unit off the roof deck. If this curb is not properly sealed or if it rots, water can infiltrate. The glass or plastic glazing itself can also develop cracks or its perimeter seals can degrade, allowing moisture to bypass the primary barrier.

Repeated exposure to sun, rain, and temperature swings breaks down sealing materials. Ultraviolet radiation makes rubber seals brittle, while freeze-thaw cycles can crack flashing and caulk. An oceanic climate with mild wet winters and dry summers subjects materials to constant moisture followed by drying, accelerating wear.

Wind-driven rain is a major culprit, as it can force water upward under loose flashing or into tiny gaps. Heavy snow and ice dams are also problematic; melting water backs up under shingles and directly against the skylight's lower edge, finding any weakness in the seal.

A professional roofer can perform a thorough inspection, often using moisture meters to detect hidden dampness in the roof deck around the skylight. They will check the integrity of all flashing points, the sealant bead, and the condition of the shingles or roofing material surrounding the unit.

The repair might involve resealing, replacing sections of flashing, or in some cases, reinstalling the entire skylight. After the roof leak is fixed, water damage pros use tools like moisture mapping and structural drying to ensure all affected building materials are dry to prevent mold and structural decay.