How do you stop a skylight from leaking?

Diagnose the source

• Condensation: water beads on the inside of the glass and drips on cool mornings or after showers, even in dry weather. That is humidity, not a roof leak; improve ventilation and run bath fans.
• Glazing seal: drips at the glass edge during rain, or fog between the panes, point to a failed seal.
• Flashing: stains on the drywall shaft below the upper corners, especially in wind-driven rain, point to the head or step flashing.
• Debris dam: leaves and pine straw piled on the uphill side push water under the flashing.

Short-term steps

Clear debris from the uphill side, check that the flashing is not lifted, and seal any exposed fastener heads. A tarp over the skylight is fine for an emergency. Running caulk around the entire frame often traps water and makes the eventual fix harder.

The lasting fix

Skylights are flashed much like a chimney: a head flashing on the uphill side, step flashing along the sides woven with each shingle course, and an apron at the bottom. Good practice adds a self-adhered membrane up the curb before the metal goes on. Replacing that flashing means pulling shingles back, so it pairs naturally with a roof replacement. If the unit is fogged, cracked, or about as old as the roof, replace it at the same time; see replacing skylights with your roof and flashing explained.