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)
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To learn more about roofs and attics, see these other blog posts:
• Why is my roof sheathing sagging between the trusses?
• Why is granule loss a problem for an asphalt shingle roof?
• What are the mistakes to avoid when doing attic improvements?
• What causes roof shingles to curl up at corners?
• What causes shingles to buckle along a line on the roof?
• What causes a sagging roof ridge line?
• What causes bubble-like blisters in a built-up and gravel roof?
• Why does it cost so much more to replace a steep roof than a low slope roof?
• What is "ponding" on a flat roof?
• Is an attic required to have a light by the building code?
• How can I inspect my roof for hurricane damage?
• Why is premature curl of roof shingles a problem?
• How can I tell if a roof has more than one layer of shingles?
• What are the common problems with attic insulation?
• What is the life expectancy of an asbestos cement shingle roof?
• What's the average lifespan of a roof?
• Why is it a mistake to replace a roof and not replace its flashings?
• Why is there no attic access hatch in the house?
• What is the building code requirement for an attic access hatch, scuttle, or door?
• Does a roof with multiple layers of shingles last longer?
• What can I do to prevent roof leaks?
• Are roof trusses better than roof rafters (stick framing)?
• Why is a popped nail in a shingle roof a problem? How do I fix it?
• What are the most common problems with wood roof trusses?
• What causes a lump or dip in the roof?
• If my roof is not leaking, why does it need to be replaced?
• How can I be sure my roofing contractor got a permit?
• How many layers of roofing are allowed on a home?
• What are the dark lines running parallel to shingles on my roof?
• Can metal roofing be used on a low slope/pitch roof?
• How can I make my roof last longer?
• What are the warning signs of a dangerous attic pull-down ladder?
• How can I find out the age of a roof?
• Should I buy a house that needs a new roof?
• Should I buy a house with an old roof?
• What are those metal boxes on the roof?
• What does "lack of tab adhesion" in an asphalt shingle roof mean?
• Why do roof edges start leaking?
• Do home inspectors go on the roof? Do they get in the attic?
• Should I put gutters on the house?
• How much of a roof truss can I cut out to make a storage platform in the attic?
• What's the difference between an "architectural" and a regular shingle roof?
• What does a home inspector look for when examining a roof?
• Do stains on the ceiling mean the roof is leaking?
• How can I tell if the house needs a new roof?
• Why does my homeowner's insurance want a roof inspection?
• What are the hazards to avoid when going into an attic?
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.