Plaster ceiling water stains under flat rubber roof


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Old 02-26-21, 11:09 PM
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Plaster ceiling water stains under flat rubber roof

I am attaching a photo of ceiling stains on an old plaster ceiling covering about approximately a square yard area. The roof above is flat and covered with EPDM rubber. The room is generally warm during the winter in the NE. There were a couple of good snowstorms and I did not shovel the roof. Most of the snow is now gone, but recently the roof area above the stain was covered in ice. As this is now melted I have gone over the membrane and find it to be absolutely intact. I do not know how there could possibly be any leakage and I am puzzled by the large area of the stain. Could someone help on this? Thanks very much. Please disregard the first image.

 
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Old 02-26-21, 11:40 PM
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Things can look waterproof but may not be. Take a shower pan membrane for instance. You must do a 24 hour water test on it to know for sure. If it holds water, and there is no leakage you're good to go. Your epdm is like a giant shower pan. The only way to know if it leaks for sure is to fill it up with water and see if it leaks. Water at the edges, or anywhere for that matter, would all likely run downhill to the center of the room because that is where the sag will be from years of deflection.

If its not leaking, the stain could be from frost. Thin underinsulated ceiling joists... no vapor barrier... combined with the snow and ice on the roof. Just a guess though.

It's more likely that there is a leak somewhere, maybe at a seam, edge, parapet, wall, scupper or coping. If there was never a stain before, and it's just suddenly appeared, its more likely to be a leak than from frost.
 
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Old 02-27-21, 08:45 AM
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I really appreciate your thoughtful reply. How often do you see EPDM become porous? I don't believe I've ever seen that mentioned. This roof looks almost new (it's 7 years old), nice sheen, no greying or rough serface. I'd tend to rule out a porosity issue. Also I've checked for small dents and scratches and found nothing (I've rarely walked on it.) Whatever, a good EPDM roof coating should work, but before I purchase I'll look further.
I do think your "bowl" theory has merit. This is a very old house (20's) and there is some depression in this area. I rule out most edges but I will look again at the one existing seam and the edge that butts up against the house. There is a small angle so water will run down from the house edge and across the seam to the suspicious area. Will again check the seam and the wall caulk as well.
To expand one of your ideas. The space between the roof and the ceiling is uninsulated and probably not completely air tight. Would it make sense that with ice sitting on the leak area for a long time and a warm room, that condensation could form much as in the case of a cold glass of liquid in a warm room? I guess this is what you were alluding to, but thought it was a long shot (as I do.)
I will keep you posted. In other years I have always shoveled the roof after a snowstorm but this year didn't for the first time after heavy snow. I think this may have been a factor as, with a warm room below, it would allow water to be against the roof for many days (weeks?) until the snow completely melted thus aggravating.any potential breaches.
 
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Old 02-27-21, 12:29 PM
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The thing is... If you never had a problem before, what changed. If the roof has always been kept scooped but this year it was covered in ice... Yeah that could lead to more frost. Hard to believe it's uninsulated. I saw so much frost in one attic before that when it thawed, it was like a pipe had broke. It was just running out of the ceiling and down the walls like someone had turned on a garden hose. So I know it happens. Whether that's what it was, no good way to know.

As for a solution, I'd rip the whole ceiling down to the joists and have it commercially spray foamed before you put up new drywall. Once you open it up you could maybe use a hose to look for any leaks. If you don't find any and it doesn't leak when it rains... Possibly frost then.
 
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Old 03-01-21, 11:12 AM
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I wasn't going to rule out coincidence so wasn't sure about not shovelling being the culprit. But the more you say, the more I am concvinced that frost was at fault. The last remaining patch of ice on the roof was directly above the soiled area. The photo I sent wasn't very good, but it should have clearly shown a ceiling area 2-3 feet in diameter with mild discoloration, evenly distributed. I don't think a leak with a single source would have done that, do you? On Wed. I will double-check the caulk line at the exterior wall and the one seam several feet downstream from it, and will again look for epdm punctures, but I do think you've nailed it. And from now on I will go back to shoveling! Don't know how many more snowstorms we'll have here in MA.
Do you have trouble sleeping? I do too and never fall asleep much before 2am.
Again, your terrific help is very much appreciated!!!
 
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Old 03-01-21, 11:29 AM
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Do you have trouble sleeping?
Sometimes I'm up late and when I go to bed my brain won't shut off.

Glad to help. Hope you get it whipped.
 
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Old 03-02-21, 02:48 PM
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Just curious: What is the risk of a puncture or even a cut when you shovel the roof? Is there a special roof shoveling scoop?
 
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Old 03-03-21, 08:07 AM
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Good question. I use a plastic shovel, not metal, and I try to leave a protective layer of snow so I don't scrape. I inspected the roof again this AM and it looks flawless.
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