Ask the Carpenter: Tracing those mysterious ceiling stains

Ask the Expert Home Improvement
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Q. We are at a loss and hope you can help. We own a house built in 1930. We replaced the roof about 12 years ago; it is a hip roof with asphalt shingles over tar paper with a rubber liner around the edges. It remains in good shape, with no curling or fishmouthing of the shingles or visible cracks; however, a water stain has appeared on the ceiling in my son’s second-floor room, centered above a window that is in the middle of the wall. We first noticed the stain at the beginning of the summer, when we put in the window air conditioner (which we remove seasonally), and it has steadily grown.

The attic above is unfinished, and the stain appears to have grown along a ceiling joist, as it has a very regular, linear appearance. We have examined the attic and so has a roofer and a carpenter who was working on the house. We also have examined the roof from the outside, and a contractor with whom we have worked in the past has done the same, as did the roofer. Nobody has been able to identify where the water is coming from.

We placed newspaper across the ceiling joists in the attic in the area around the stain to see whether we could identify where the water is dripping from (we thought maybe it was coming in the ridge vent), but the paper has not gotten wet even though it covers the area of the stain for about 5 feet in either direction. We have not seen any other ceiling stains, so the leak seems to be isolated. The ceiling is starting to crack. What could be causing it?


A. Wow, it sounds like a lot of qualified folks have had eyeballs on this, so I feel at a disadvantage. It was smart to lay paper down on the joist. I suggest looking in four places. First, next time it rains, you need to scour the attic space with a bright flashlight, looking and listening for drips. Second, you need to reexamine the rubber roof seams. Third, I’d look closer at your gutter/fascia area. Is the gutter clogged and full of water? Is water leaking in at the edge of the roof fascia and running on the top of the ceiling boards before showing up as a leak? Lastly, I’d look at the top of that window and inspect the top trim flashing to ensure that it is not damaged and allowing in water.


Q. We have an odd problem that I’ve never seen anywhere else. The top-floor bathroom in our 1911 house is in a gable. When we gutted and rebuilt it years ago, we opened up the ceiling to make the room look bigger. We put in a pretty powerful vent fan, and there is a large window plus an AC vent, so the room is as well ventilated as a bathroom could be.

We often get darkish brown spots on the ceiling that look like varnish drips or something similar. My husband (who works in the construction industry) thinks it is dust caught in condensation, but I don’t ever see much condensation. There are none of these spots on the vertical walls of the bathroom, just on the slope of the ceiling where it follows the lines of the gable. We wash them away periodically, but they return, not necessarily in exactly the same places.

What is causing these brown spots, and what can we do to prevent them from coming back?


A. Your husband is correct. The same thing happens in my bathroom, which has a cathedral ceiling. I also have a powerful fan set on a 30-minute timer. This fan is no match for my wife and two daughters and their super hot, super long showers. Unfortunately, you are going to have to keep washing away those stains.

Rob Robillard is a general contractor, carpenter, editor of, and principal of a carpentry and renovation business. Send your questions to or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at