Flashing and Skylights: How Can You Be Sure Your Skylight Is Water-tight?

Susanne Clemenz

Skylights can brighten up a room, especially one with shaded windows. Some bathrooms, utility rooms, and closets have no windows, so skylights can provide natural light and ventilation. You'll need to weigh the advantages of skylights against the possibility of roof leaks. Correct flashing installation often is the critical factor.

Climate Affects How Well Flashing Systems Perform

The function of flashing is to provide an impervious barrier to water seepage. Consider these questions:

  • Does snow, perhaps a lot of it, sits on your roof for weeks or months at a time?
  • Do you experience fierce winds with driving rains from time to time?
  • Does your roof have previous or current leaks?
  • Do you want the skylight in a kitchen or bathroom where the extra moisture may cause skylight condensation?

What Type of Skylight Flashing Systems Are Available?

Skylights can be operable, stationary, cylindrical, manufactured, or custom-made. Flashing materials are aluminum or steel sections fitted closely to the skylight. Flashing materials may also include caulking and other waterproof underlayments. There are various flashing systems available:

  • For manufactured units with 2- to 4-inch high curbs, there are top (header) and bottom (sill) flashings with soldered joints at the corners, and overlapping side units. Flashing is nailed to the curb, not the roof, to discourage leakage. Correct installation starts with the bottom flashing, which goes on top of your shingles, and progresses to the top. Side and top flashing go under your shingles. Homeowners must make sure weatherproof gaskets are kept pliable and unbroken, so no debris gathers on operable gaskets, and that the skylight closes completely. Regular inspections are essential.
  • Flush-mounted skylights are fixed panes inset with L-brackets into headers which project enough to receive one-piece soldered head and sill flashings. Side flashing consists of L-shaped step shingles that match your roof. They overlap from the bottom up, and are woven under the roofing shingles, matching their overlap.
  • Correct flashing installation for tubular skylights includes positioning a short, pipe-like cylinder with a flange that radiates out. The flange is slipped under the shingles.

Before you purchase a skylight, have your roof and attic inspected for leaks, and repair any problems. This avoids confusion if a leak occurs after installation. And remember that skylight condensation can seem like a roof leak, but isn't. Only you can weigh risks against benefits, but correct flashing installation by an experienced skylight installer can provide the peace of mind you're looking for!


About the Author
Suzanne Clemenz designed her passive solar home and interacted with the contractors every day of the 6-month project. She started drawing floor plans and making models in the early '70s after purchasing several building lots. Recently she expanded and remodelled her newly-purchased home, working with contractors on the floorplan, electrical changes, painting, installation of wood laminate flooring, flood prevention walls and stonework, major drainage issues, an irrigation system and a landscaping. Researching and keeping up on issues and products related to home design and maintenance is an ongoing avocation.

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