Why do my dormer windows leak?

Monday, September 10, 2018

Although dormer windows have walls and a roof, just like the main structure of the house below them, they are a roof penetration—the same as a skylight, chimney, or plumbing vent pipe. Once you understand this, along with the fact that all sides of a dormer must have flashings that are properly installed and maintained in places where they meet the roof—which is all the way around—you see why they can be a problem.

   This issue is compounded in some newer homes, where the designer used dormers only to dress up the roof for the curb appeal of the home. They are not part of the occupied area of the house and open into the attic, or are simply applied over the roof sheathing. Many people them called “fake dormers,” but builders prefer the label “inactive” or “passive” dormers, as opposed to “active dormers” that open into a living space and provide natural light. Any minor leaks are not observed in passive dormers until they become severe enough to stain the ceiling of the home below. 

   What can you do? Assuming the dormer structure and window are installed correctly, you want to check them regularly for any wood rot at the window trim or staining around or below the windows. If you are not comfortable on a roof, looking with a pair of binoculars will do. 

    You can also check in attic for signs of leaks at passive dormers that have an opening into it, being careful to only step on the bottom chords of trusses or ceiling joists where attic flooring is not installed. Here’s a few of the defects that can cause dormers and their windows to leak:

  1. Improperly installed or deteriorated roof-to-wall flashings.
  2. Lack of flashing at top of trim over window.
  3. Deteriorated caulk around window
  4. Roofing leak at dormer roof
  5. Roof damage from falling branch or hail  

    Many homeowners also have a licensed roofer walk their entire roof every year or two to report on the condition and make any minor repairs.

    Also, see our blog post The inspector says that a missing kickout flashing caused water damage inside the wall. What's "kickout flashing"?



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