Why is My Skylight Leaking? Should I Seal My Skylight?

Skylights can be a wonderful asset to your home. They add natural light and save energy by reducing the need for artificial lighting, and some open and close to provide additional ventilation. Skylights are not such a joy, however, when they leak.

Almost all skylights will leak at some point, and the cause is usually one of three things: improper installation, a broken window seal or deterioration of the flashing. If your skylight wasn’t installed anytime recently, one of the latter two is to blame.

Sealing a Skylight

To figure out the cause of the leak, you’ll have to climb on the roof and do a test (or you can hire a professional roofer to do this if you’re uncomfortable). Run water from the hose over the skylight and pay attention to the leak. If there’s water where the glass and window meet, you have a broken seal.

There are two ways to address a broken seal: resealing or replacing the skylight entirely. Resealing is fine if the leak has not yet caused moisture and condensation to collect between layers of glass (we’ve all see those opaque-looking skylights), but replacement is the only option if condensation has already formed.

Resealing and replacement are usually best left to professionals, but those experienced in DIY projects may be able to handle the work. Professional resealing usually costs about $300 to $600, while replacement costs anywhere from $500 to $2,000 or more, depending on the type and size of skylight, and your geographic location. Generally, replacement is much cheaper when your roof is being replaced - the cost might be $800 during roof replacement but $1,600 any other time.

Re-flashing

Flashing is metal barrier that is placed over roof joints to prevent leaks and moisture problems. Flashing is always installed around skylights to serve as a line of defense against water leaks, but sometimes it fails.

Skylight flashing is replaced by peeling back the roof shingles around the skylight, installing new flashing and then replacing the shingles. A DIY kit to fix the problem costs about $100, but that’s not advisable unless you’re handy because you could damage nearby shingles or cause yet another leak. Hiring a professional to do the job costs about $300 to $500 on average.

Other Causes

Broken seals and faulty flashing are the two most common causes of leaky skylights, but sometimes the problem is simpler or less obvious. Here are a few things to look for before you call the roofing contractor:

• If your skylight opens and closes, is it fully closed? Some people mistakenly assume that the skylight is faulty not realizing it was left (slightly) open.
• When does the leak occur - only when there’s snow and ice on the roof? Only in the fall? Check the area near the skylight to make sure ice, snow, leaves and other debris are not blocking water from sliding off the roof.
• Is the flashing damaged elsewhere on the roof? Leaks in other areas of the roof can send water traveling underneath the shingles and toward the skylight. This problem will likely require a professional fix, but you might save some labor hours by diagnosing the problem on your own.

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