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The Times
  • Q-and-A: Why does my skylight leak?

  • Anytime there is a roof penetration, such as a chimney, plumbing vent or skylight, the chances are very likely it will leak. I don't know what kind of skylight you have, but there are two main reasons a roof penetration leaks.

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  • Q: My husband and I are at our wits' end with our leaky skylights. We covered a brick patio in the mid-1980s with a pitched roof with three "long lights." The amount of light transmitted into the outdoor space, as well as our family room, was wonderful.
    After several years, the skylights leaked uncontrollably. We replaced the long lights with domed skylights. Eventually, they also leaked. We were told that the problem was the roof, which we replaced. Twenty years later, we still have leaky skylights, and I am ready to pull the entire structure down and replace it with a pergola. We are ready to downsize and my husband feels the covered patio is a great selling feature. Can you offer any suggestions?
    A: Anytime there is a roof penetration, such as a chimney, plumbing vent or skylight, the chances are very likely it will leak. I don't know what kind of skylight you have, but there are two main reasons a roof penetration leaks:
    -- A low-pitched roof that drains so slowly during a heavy rain that water actually ponds on the roof's surface. A roof covering is water-resistant, not waterproof, so low-pitched roofs must have additional water barriers under the shingles or roof coating.     
    -- The skylights were not installed or flashed properly. Flashings are custom made for each application, and they are designed to divert water away from the item that penetrates the roof's covering. Metal flashings are commonly used in residential construction because they are easy to form, and, when installed properly, they will outlast the life expectancy of the roof coverings.
    In some cases, a rubberized, self-adhesive flashing material is used in conjunction with metal flashings to form a waterproof seal. When only metal flashings are used, they must be sealed to the roof's decking with a roofing mastic, as well as metal fasteners.     
    As a builder, the only skylights I would install were "curb mounted." I refused to install any of the low-profile, bubble-type skylights because I found them impossible to flash and seal. A curb-mounted skylight is one that has a frame that is raised about 4 inches above the roof area, and a quality-built skylight will have built-in flashings, making installation easier.
    I would imagine a patio roof has a low slope, and water will pond on the roof before it has a chance to drain. If you have the low-profile skylights or you want to use the dome or tunnel skylights, a carpenter can build a frame between the rafters so the skylights can be elevated above any ponding water.     
    The custom frame is then flashed with metal flashings or a self-adhesive rubber coating, and then the skylight is installed atop the new frame. Examples of various types of skylights can be found at http://www.veluxusa.com/.      
    Page 2 of 2 - Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at C. Dwight Barnett, Evansville Courier & Press, P.O. Box 268, Evansville, Ind. 47702 or e-mail him at d.Barnett@insightbb.com.    

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