How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

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What causes leaks at a fake roof dormer?

Friday, June 15, 2018

We often hear them called “fake dormers,” but builders prefer the label “inactive” or “passive” dormers, as opposed to the “active dormers” that open into a living space and provide natural light. The big difference between leakage in a passive dormer and an active dormer is that leaks in a passive one do not get noticed as soon. Water intrusion is not observed in passive dormers until it becomes severe enough to stain the ceiling of the room below.

    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.


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

    You can also check in the 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 or roof-to-roof valley flashings at top back of dormer.

2) Lack of flashing at top of trim over window.

3) Deteriorated caulk around window and sill.

4) Roofing leak above dormer due to age deterioration or poor installation.

5) Roof damage from falling branch or hail (not always visible from the ground)  

     Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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