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Tips on preventing skylight leaks and curing the ones that do leak
Thirty years ago, when I first went into construction, an old carpenter wisely told me, “Son, there ain’t but two kinds of skylights, those that are leaking, and those that are going to.” If you want to prevent skylight leaks and/or cure the leaks that you have, it will require diligence, trial and error, and a lack of agoraphobia (fear of heights), which is not to be confused with angoraphobia, the fear of fuzzy sweaters.
NEW SKYLIGHTS
Most new skylights now come with self curbing flashing. What this means is that you, the installer, do not have to build a curb, or raised box, for the skylight to rest on. For installation into an existing roof, follow the manufacturer’s directions for cut-out and framing. Read the installation manual very carefully. The directions will give you specific points to use the provided silicone sealant, usually at all corners and joints. Really the only additional areas of concern if you have followed the instructions dutifully, is to seal the roofing material to the flashing as you are installing it. Make sure that your flashing fits under the roofing at the top of the skylight only, and that it is above the roofing on the sides and bottom. Purchase a tube of asphalt roof sealant to seal shingle roofing to the flashing, or silicone sealant for other roofing materials, as indicated in the instructions. Pay close attention to any exposed screw heads and put a dab of clear sealant on those too.
EXISTING SKYLIGHTS
Here is where the rubber meets the road, so to speak. Anything penetrating the surface of your roof is exposed to tremendous amounts of heat, humidity, moisture, freezing, hail damage, tree limb damage, etc… And if you have any underlying roof problems such as mechanical shifting of the decking, inadequate ventilation, poor installation techniques of the roofing material or the skylight, you will have a leak. The surest way to know you have a leak is to watch the drywall or trim boards around the skylight. If they are wet during a rain, and it is more than just normal condensation, chances are that you have a leak. If you have attic access to the skylight well, get into the attic and check carefully with a good flashlight for water stains. If you find them, the only way to stop a leak is from outside on the roof. There is nothing that you can do from inside to stop a leak.
Safely access the roof, if the height is too much for you, the roofing material is loose or deteriorated, the pitch is 7/12 or more, or you just feel unsafe up there, STOP. Call a professional roofer, and let them attempt the repair. Your life or paralysis is not worth the money you will save doing it yourself.
If you can safely get on the roof, inspect the skylight carefully. Check all corners, exposed screw heads, flashing, joints, and surrounding roofing for water entry points. Seal all of these that you find. If your inspection reveals a breach or crack in the glass surface, you will need to replace the skylight. Press down on the roof decking around the skylight with your foot to check for rotted decking. If the decking is bad, you have bigger problems than the skylight. If the decking is OK, proceed with your silicone caulk to methodically seal all possible entry points that you can find. Start with the roofing at the highest point and move down slope on one side all the way to the bottom of the skylight, then move to the other side.
Keep in mind that your (or your roofers) chances of locating and stopping the leak on the first try are 60% at best. Don’t get upset with your roofer if you still have a leak after paying him. Just like you, he wants it fixed the first time too. I have never met a roofer who will warranty a skylight repair. It may cost you several trip charges. Treat your roofer well, he doesn’t make money off of your repair, and it takes him away from money making larger jobs. And you will need him in the future.
If the leak persists after several attempts at repair, the curbing or the insulated glass may have failed and you will need to replace the skylight. The best defense is a good offense, so you should either check out your roof yearly and seal any roof penetrations that you see, including the skylight, or have your roof inspected by a professional yearly.
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