If you're installing a self-flashing skylight, you're now ready to position the skylight. But if your skylight is a curb-mounted unit, you need to flash the curb. Your skylight might come with a flashing system, as shown in the video. Be sure to follow the manufacturer's instructions carefully. This is the most critical part of the skylight installations bad flashing job can result in a leaky roof.
Unless you've worked with sheet metal and have a propane torch or large soldering iron, you'll want to have a sheet metal shop make the flashing pieces for you.
If you do decide to make your own flashings, use lead, it's easier to work with than copper or aluminum. With little effort, you can bend and solder lead and solder the joints between flashings for a long lasting, watertight seal. Make paper patterns of the flashings to fit the curb; form the pieces, and then solder the joints in the saddle and apron flashings.
Flashing a curb so it forms a watertight seal between the outside and inside of your home requires special care and thoroughness. If you follow the instructions below, and any guidelines from the manufacturer of the skylight, you should be able to enjoy the raindrops dancing on your skylight, instead of dripping into your house.
Slide the saddle, or top flashing, underneath both shingles or shakes and the roofing felt. Remove any nails that keep you from sliding the saddle all the way up under the shingles. As you position the saddle, take care not to puncture the roofing felt, as this can cause leaks.
Set the curb over the roof opening, sliding it up from the bottom until it's perfectly aligned with the opening. Check the curb for squareness. Then, using 16-penny nails, toenail the curb through the sheathing to the frame (rafters and headers). Remove the corner braces from the curb.
At the top of the sloping of the curb, place step flashing underneath each end of the flange on the roof. Remove the skylight and liberally cover the area within the lines with roofing cement.
Next, position the skylight over the opening, making sure all four corners are aligned with the corners of the roof opening. Press the flange firmly into the roofing cement and nail the flange to the roof with the roofing nails. Cover the nail heads and the flange with a generous amount of roofing cement.
If your roof is surfaced with hot-mopped asphalt or with polyurethane foam, you may want a roofing contractor to restore your roof. You can replace shingles or shakes yourself; trim them as necessary to fit against the edge of the curb.