Bathroom Ceiling Leak: Leak in plumbing vent pipe flashing leaves stains on bathroom ceiling

Janet asks,

I think I may have a bathroom ceiling leak. I discovered a water stain all around the ceiling in our small bathroom, and a few weeks later noticed another water stain in the shape of a circle more than a foot in circumference about 6 inches in from the original water stain all around where the ceiling meets the walls. We had a plumber come in and he sawed a hole in the ceiling and found nothing leaked! We live near the ocean and the bay in New Jersey and were told that possibly the wind blew in rain. Could this really be the problem behind our bathroom ceiling leak?

Our Answer

Yes, it is possible this is the source of your bathroom ceiling leak. In fact, most ceiling leaks in bathrooms are caused by leaks in the plumbing vent pipe flashing above the bathroom where the vent pipe goes through the roof. Plumbing vent flashings are manufactured aluminum flashing sections with rubber gaskets that surround the pipe. Over time, the rubber breaks down and rainwater leaks through the roof, drips down around the pipe and ends up on the ceiling above the bathroom. The fact that this happens only periodically may be due to wind-driven rain, causing leaks only when the rain is driven from a particular direction.
The first step to a cure for this bathroom ceiling leak source is to evaluate the rubber portion of the plumbing vent flashing I described above. If you find it is cracked, torn or just deteriorated, you can replace it or just reseal it with asphalt roof cement.
By the way, we hate the fact that the first thing too many plumbers do in situation like this is to rip open a ceiling! Frankly, there are many less-destructive ways to track down bathroom ceiling leaks that don’t involve a pry bar or a hammer!