Installing a Deck-Mounted Skylight

Skylights transform a stagnant, shadowed room into a bright, living space by capturing daylight from the best source possible: the sky. A successful installation is entirely defined by your commitment to the flashing sequence, which serves as the final, absolute defense against the elements. Before you cut into your roof deck, ensure you have a clear path from the attic side to avoid mechanical or electrical obstructions hidden behind the drywall. When done well, the unit sits perfectly level, integrated into the shingle pattern so that water flows effortlessly around the frame rather than against it.

  1. Locate and cut the opening square. Locate your rafters from the attic, then drill four pilot holes upward through the roof deck to establish the exact corners. Use a reciprocating saw to cut the roof deck from the outside, keeping your cuts square to the rafters.
  2. Build square support headers. Install header beams between your rafters to support the cut ends, ensuring they are flush with the existing rafter layout. Secure the headers with heavy-duty structural screws driven through the side of the rafters.
  3. Seal the curb perimeter tight. Build a wooden curb around the perimeter of the opening, rising roughly 4 inches above the roof surface. Secure the curb to the roof deck and rafters, ensuring all joints are tight and perfectly squared.
  4. Wrap with waterproof barrier. Wrap the curb and the surrounding roof deck with self-adhered waterproof underlayment. Overlap the seams generously, starting from the bottom of the curb and working your way up to ensure water sheds outward.
  5. Mount frame dead square. Place the skylight frame over the curb, ensuring it is centered and square. Use the manufacturer-provided mounting brackets to screw the frame securely into the side of the wooden curb.
  6. Interweave flashing with shingles. Work from the bottom up, installing the sill flashing, side step-flashings, and finally the head flashing. Interweave the step-flashings with your existing shingles to create a continuous water-shedding path.