skylights, condensation and leaks

To solve leaks and condensation problems hire an experienced skylight professional/roofer. In many situations, solutions involve lifting parts of the roof, sealing, reinstallation or replacing of membranes and protective cladding, repairing of drywall tunnels associated with the skylight, etc.

Episodic Condensation

Extreme outdoor temperatures – below, say, 10º or 15ºF (9º-12ºC) - combined with high interior water vapor, can cause condensation, even if you have the best skylight, properly installed. That condensation isn’t truly a problem, if episodic and associated with extreme temperatures. The problem happens when there are leaks and condensation occurs in normal and common weather conditions.

Internal sources of condensation

Do not underestimate internal sources of condensation, and the possibility of problems due to them. People, plants, cooking, baths or laundry are a source of warm air which may condensate in skylights and its structures and be a cause of problems.

Indoor warmer air and water vapor may escape around the opening created for the skylight installation, where they often condensate, coming back into the house as water.

Problems with shafts

Some leaks and condensation problems have their sources at the skylight tunnel and drywalls around it. Possible gaps between the framing lumber and the skylight should be carefully sealed with a foam sealer. An interior vapor retarder is also often applied over the sides of the shaft or roof framing and over the foam.

Roof and flashing leaks

If your skylight doesn’t have appropriate underlayment and protective cladding, ice damming is a source of problems, even if the skylight has a good flashing system.

Problems involving the underside of metal flashing – due to deficient installation, materials, or design - are also a cause of condensation and leaks. Outdoor water and moisture can penetrate through them.

Current sealing

Flashing and underlayment are crucial and possible problems and deficiencies involving them should be fixed. But complementary sealing systems around the skylight structures can also be responsible for leakage.

If the water appears in or around the exterior of the skylight, sealing possible leaks associated with seams and joints is important. Lift the shingles next to the skylight, and clean them and around them. You must study the roofing cement where shingles meet the skylight borders, looking for water sources. Any seams and joints should be sealed with silicone or, preferably, urethane foam roofing.

Ice dams and skylights

In cold climates, the flashing systems of many skylight models aren’t enough to block the water associated with ice-dams. In this case you may install ice-dam protective cladding materials and membranes, between the roof deck and the sides of the skylight/flashing system. Asphalt and rubber membranes, carefully applied, can block possible water paths.

See: Skylights in rainy cold climates

Skylights and their glasses

Skylight condensation can be caused by an inappropriate glass. In this case, the best thing to do is to replace the skylight with a modern qualified one:

See: Skylights and glasses.