For a leakproof skylight use a special flashing kit and installation techniques we show here.
Install 6-in.-wide strips of a self-sticking waterproof underlayment. This underlayment will direct any water that may get through the metal flashing onto the roofing felt. Install from the bottom up, lapping each piece on top of the lower one.
Set the bottom one-piece flashing on top of the shingle course. Nail it only at the upper corners; don’t nail it into the roof.
Weave the step flashing up the side of the skylight as you install each shingle course. Nail at the upper corner.
The top (head) flashing is one piece that wraps around the sides. This fabricated piece has soldered and sealed seams and corners. Fit and install the next row of shingles, leaving about 1/2 in. of flashing exposed.
If you have to replace shingles around a skylight, examine the old flashing. Most residential skylights sit on a raised curb made watertight with metal flashing. If it’s carefully removed when the old roof is torn off, it should be reusable. If not, you’ll have to buy new flashing ($50 to $100) either from the skylight manufacturer or from a roofing company that has a metal fabrication shop (look under “Roofing” in the Yellow Pages or online).
First remove the skylight’s counterflashing. On some units, you have to remove the whole glass frame (lead photo below). On other models, you simply unscrew a metal channel from the curb. Next pry off the old shingles, carefully pulling nails to save the flashing. To reassemble, follow the steps as outlined by the photos, and you’ll have a leakproof installation. Note that the metal flashing pieces don’t need to be sealed to each other. Since water runs downhill, they only need to be installed in the right order. So put away that roofing cement.
If you’re hiring a roofing crew, ask them to carefully remove the old flashing and reuse it if it’s in good shape.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.