Sealing around a leaking skylight requires a thorough approach that addresses both the glass seals and the exterior flashing system where the unit meets the roof deck. First, thoroughly clean the entire perimeter of the skylight, removing all dirt, old degraded caulk, leaves, and moss so that new waterproofing materials can bond effectively. Inspect the metal flashing pieces surrounding the base of the skylight for gaps, lifted edges, or rust holes, and apply a generous bead of high-grade, exterior-grade polyurethane or silicone sealant beneath and over the loose flashing joints. If the leak originates higher up where the glass meets the frame, apply a specialized structural glazing sealant designed for continuous outdoor exposure. However, if the flashing kit itself is heavily deteriorated or improperly installed underneath the surrounding shingles, applying surface caulking will only serve as a temporary band-aid, requiring professional flashing replacement for a permanent fix.
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