Step 2: Flash The Sill

install watertight skylight take out roof piece, add roof sheathing around edges
Photo: Anthony Tieuli
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Have a helper inside carefully lower the cutout as you cut the fourth side. Nail the roof sheathing down around the perimeter of the opening. Stick a strip of self-adhesive membrane across the bottom edge of the opening, as shown. Cut and fold the top 1 inch or so of the strip over, onto the exposed sill.
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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