How to Install a Leak-Free Skylight

Dear Pat: I would like to install a skylight in my living room ceiling. I am a little concerned about this project because my neighbor's skylight always leaks during storms. What is the proper way to install one? — Karen L.

Dear Karen: If you talk with any builder who has installed many skylights, he will tell you there have been some leakers. They generally do not leak often, but when there is a severe storm, which can blow rainwater at unusual angles, the water can get up under the shingles and skylight flashing. From there it follows the framing and drips down somewhere from the ceiling.

There are some newer products and tricks of the trade to minimize and, perhaps, eliminate leaks even during the most severe storms. First, though, you must use the standard basic techniques for creating a stable opening in the roof and ceiling for the skylight.

It will be a lot easier and better to install a skylight sized to fit perfectly between the rafters, which are on 16- or 24-inch centers. Almost all the skylight companies offer skylights in these widths. The only problem with this is the skylight might not be centered perfectly in the ceiling.

If it is important to you to have it perfectly centered, you will likely have to saw through an existing rafter. If you do this, it is wise to add sister rafters next to the ones on each side of it for a double thickness. Install 2x8 headers at the top and bottom of the opening.

Once the framing is completed from indoors, drill holes and install long screws in the corners so they extend up through the shingles. These indicate the precise location of the skylight on the roof.

Before you go up on the roof to cut the hole, wear proper safety support gear in case you slip. Take your cell phone along. Also, always let a nearby neighbor know when you are working on a roof so they can check on you and hear you call for help if needed.

You must be careful working with the shingles, especially if they are older and brittle. The center ones will be removed, but the perimeter ones will become part of the water sealing system with the skylight flashing. It is usually easier to loosen the self-adhesive strip on the shingles when they are cool.

Once the shingles are removed and loose, work on the underlayment layer. Using a chalkline, snap the cut lines from screw to screw on the underlayment. Cut the corners at an angle and fold the underlayment back several inches on each side. Remove the screws and saw the rectangular hole through the sheathing.

Remove the glass section from the skylight and screw the skylight frame over the hole. It is usually attached with metal angle brackets. For the best leak-free seal, cut one-foot-wide strips of self-adhesive flexible plastic roof membrane.

Stick one edge of the membrane against the vertical sides of the frame. Stick small reinforcing pieces at the corners. The other side should stick to the underlayment that is folded up. Next, fold the underlayment back flat against the roof. Install metal step flashing over the underlayment and under the shingles. Reinstall the remaining shingles and the skylight top over the frame per the manufacturer's instructions.

Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com. To find out more about Pat Logan and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.