How I Did It: Installing a Skylight


1 How I Did It: Installing a Skylight

Light spilling down from a skylight can improve the aesthetics of nearly any room. But sawing into your roof is not a do-it-yourself project to undertake on a whim—it can't be undone if you make a mistake.

However, with careful measuring, installing a skylight is doable and affordable. My husband and I recently completed one in our home. We bought the skylight and flashing kit needed for our installation for around $320, and after adding the few other needed materials our project still came in at under $400. That's at least $1500 less than what we would have paid a contractor to do the same job.

Here's how we did it. To see this project in action, watch our videos on YouTube. (Video 1, Video 2).

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2 Step 1: Cut Opening in Drywall

After we decided approximately where we wanted the skylight, we located the two ceiling rafters that would straddle the ceiling opening we made. A stud finder works well for this. Remember that rafters are commonly 2 feet apart on center rather than the standard 16 inches for wall studs.

We inserted the keyhole saw into our drywall ceiling near the middle of where the skylight will be located. We then went up to the attic to find the hole and make sure there wasn't anything between the drywall and the roof that would get in the way of the skylight. (Rerouting ductwork, plumbing, and electrical is certainly doable, but if it's easier to pick a different location for your skylight, it makes sense to do it.) This way, if you find something and decide it'd better to move the skylight, you only have a small hole to patch in the ceiling. It's important to catch things early.

We found no obstructions, so next we checked the instructions that came with our skylight to determine its exact size and how large an opening we needed to make.

Measuring from a straight wall, we used a chalk line to mark the dimensions of the opening. From our hole near the middle of where the opening would eventually be, we used the keyhole saw to cut from rafter to rafter (that's the distance our 22.5-inch skylight was made to fit.) Then we sawed along the rafters until we reached the top and bottom lines we'd marked with the chalk line, and used a utility knife to cut the remaining two lines.

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3 Step 2: Cutting the Opening in the Roof




4 Step 3: Installing the Skylight

To install the skylight fixture, you need to expose the plywood around the roof opening you just cut, out to about 16 to 24 inches. To do this, you use a cat's paw to find the nails holding down the shingles; we pried them up so as to gently peel the shingles away from the plywood (if you do this carefully you should be able to reuse the shingles once the skylight is in place). We then pried any loose roofing nails so we had a totally flat surface to work from.

Once that was done, we covered the exposed plywood with ice-and-water roofing underlayment on all four sides of the skylight hole. We cut 12-inch-wide strips.

We then set the skylight over the top of the hole. It's best to have a set of eyes from inside the house so you can line it up with the side of the rafter and the opening in the plywood. If you cut the hole correctly, you should have wood on all four sides on which to nail the flange (that's the lip around the skylight that has prepunched holes through which you'll nail it to the roof).

After nailing down the skylight, we used an extra layer of ice and water roofing underlayment to cover its edges and sit under the step flashing.

5 Step 4: Installing Shingles and Flashing

Now we were ready to reinstall the shingles and step flashing—those L-shaped pieces of metal that divert water away from the skylight.

To reinstall your shingles, start from the lowest point, working upward. As we worked our way up, we nailed a small piece of flashing next to the skylight before we laid down each row of shingles. The subsequent rows of shingles covered this up. (We had to insert a large piece of flashing along the entire length of the top of the skylight that slides under the shingles above it. Another large piece of flashing sits above the shingles on the lower end of the skylight.)

We then needed to cut some of the shingles to fit flush against the skylight and overtop of the flashing. To cut a shingle, flip it over, measure how wide it needs to be, mark where the cut needs to be made, and cut it from the underside with your roofing knife. (Always cut shingles from the underside; trying to cut through the rough materials on top will quickly dull your blade.)

We kept nailing shingles—moving inward and upward—until we'd shingled completely around the skylight. We put a dab of Vulkem polyurethane joint sealant on any nail that was exposed (not covered by a shingle) to prevent leaks.

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6 Step 5: Finishing the Cavity

Now our skylight was installed, but we still had a hole in the ceiling that opened into the attic. So the next step was to build a frame that would allow us to drywall the edges of that cavity, creating a neat path for sunlight from the new skylight to enter the room while closing off the attic, as seen here.

To start, we installed some wood pieces we'd later use to attach the drywall. At the narrow ends of the skylight, we nailed to the rafters 2 x 4 wood backers that travel vertically (flush with the edge of the ceiling drywall up to the corner of the skylight where the drywall will slide into a groove on the skylight). We also put in 2 x 4s to fit horizontally between them just above the drywall ceiling, too, so that every cut edge of drywall in the light well would have wood to which we could attach it.


To fill the area behind the frame we just built, we used recycled foam insulation that we had laying around, but a person can use other kinds, depending on cost or climate. After installing the insulation, we tacked poly over the frame as a moisture barrier.

To drywall the cavity, we needed two 4 x 8 sheets of 1/2-inch drywall, as well as 1-5/8 screws and a cordless drill gun with a Phillips end to screw them into your wood frame. There will be a groove at the top on each side of the skylight in which to slide the sheetrock. (For a refresher, read PM's Drywall Made Simple.)

After that, all that was left was the joy of taping and painting the drywall.