Introduction

install a watertight skylight
Photo: Anthony Tieuli
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Q: I've heard that all skylights, eventually, leak. Is it possible to install one so that it stays watertight?
—Angelina Holcomb, Westwood, Mass.

Tom Silva replies: Although complaints about leaking skylights were once valid, new designs and better flashing methods have largely put an end to water-infiltration worries. In fact, the Velux skylight I'm installing here boasts a 10-year warranty against leakage.

A warranty that confident doesn't allow for shortcuts on installation, though; the flashing steps have to be followed to the letter.

On a roof with rafters, I frame the rough opening from below by doubling the rafters on the sides and nailing a doubled-up header and sill to the top and bottom of the opening, respectively. (Check with your local building inspector if you have a truss roof.) The rest of the steps take place on the roof, where a fall-protection rope and harness are a must. If you're intimidated by heights or reluctant to don the safety gear, leave the job to a pro.
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    Tools List

    • fall protection harness
      Fall-protection gear
    • chalk line
      Chalk line
    • drill
      Drill/driver
    • circular saw
      Circular saw
    • hammer
      Coil roofing nailer or a hammer
    • snap-off utility knife
      Utility knife

    Shopping List

    1. Skylight kit (includes counterflashing)

    2. Flashing kit (includes self-adhesive membrane; step, saddle, and sill flashing)

    3. Deck screws

    4. Extra roofing shingles

    5. 1½-inch galvanized roofing nails