Green Renovation: Adding Skylights, Part 6 (Final)
Final part of a six-part series, Green Renovation: Adding Skylights
Previous articles in this series explained why choosing skylights is a green renovation and how to position, prepare, cut the holes for and frame your skylights. This final article in the series on adding skylights to your old house is about flashing.
For the serious flashers, you know you don't want to pay $80 for a flashing kit when you can fashion your own flashing at a fraction of the price. So here's exactly how it's done.
The Flashing Unit
The metal flashing consists of three sections: the bottom flashing, the step flashing on the sides, and the top flashing.
Begin at the bottom. The lower flashing should be a continuous piece of L flashing that extends about 8 inches down the roof. There should be two courses of shakes/shingles under the metal. The L flashing should extend at least 6 inches beyond the sides of the skylight. You want to cut the corners of the flashing so that one flap flattens down on the roof and the other wraps around the curb.
Photo 1 shows the cut pattern, and Photo 2 shows a piece of flashing cut and in place. Tin snips are all you need to cut the metal. A little gentle pounding with a mallet will bend the flashing into position around the corner.
In all of the cuts to make flashing corners, the cut is started at the top corner of the flashing and is made at a 45-degree angle down to the crease. The pointy corners are not needed and are cut off to reduce the chance of getting injured.
You can secure the flashing with a roofing nail into the top of the curb, which will be covered when the skylight is in place.
The first piece of step flashing (side piece) is cut similarly to the bottom piece, as seen in Photo 3. Put it into place on top of the bottom flashing. There is no roofing material between these two pieces--think of them as a continuous section of flashing, seen in Photo 4. Very important: caulk the corner joint with high-quality caulk. Shoot a little caulk into the corner when you place the bottom piece; then add a little more with the first piece of step flashing.
Leave a gap. Your roofing should stop 1 or 2 inches from the side of the skylight so that there is plenty of drainage room. Don't run the shakes/shingles too close to the skylight, or you will have dams of needles and leaves build up.
The second piece of step flashing will sit atop a course of roofing. This piece is cut so that the bottom extends a couple of inches down the roof, and the side is even with the side of the skylight. Photo 5 shows a mock-up of the placement, with the shake removed for clarity.
Continue up the sides of the skylight with the step flashing, with each course of shake/shingles getting a piece of step flashing.
The top is finished much the same as the bottom. The last piece of step flashing is cut for the corner (see Photo 6) and a continuous piece of L flashing--long enough to extend 6 inches past the sides of the skylight--is cut to fit the corner (as in Photo7). The top piece of flashing should extend up under the existing shakes/shingles by several inches.
Finishing Your Skylight Curb Top
You can finish off the top edge of the 2x6 curbing with a strip of roofing felt, cut and folded at the corners so it extends a couple of inches down the side of the curb. Or you can buy narrow L flashing and fashion a cap over the top of the 2x6.
And that's it. You are flashed. All you need to do is drywall the well, heft the skylight into position, set it with the provided screws, and your skylight is in place.
Now, put on your coolest sunglasses and get ready to enjoy the natural rays of daylight flooding into your once dimly-lit room.
Jim Mallery, a semi-retired journalist and onetime registered contractor, has extensive experience remodeling, repairing, and rebuilding homes.