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A leak in the bathroom, above the kitchen, started as a small water stain on the ceiling. I opened the ceiling and determined insulation (2 insulation pieces), that was placed to absorb the sewer pipe, was soaked. After two weeks of investigation, the toilet, sewer pipe, vent piping and copper cold water pipe appear not to be the issue. The vent pipe goes to the roof, and after rain storms, that too appears to be a non-issue. I had sound insulation covering the sewer plumbing, which also covered the cold copper line that feeds the toilet.

Could this sound insulation around cold copper pipe create enough condensation over time (13 years since the house was built) that it finally came through the drywall. I realize now I should have used the black foam copper pipe insulation.

Any insight would be appreciated before I close up the ceiling.

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I'm confused...is there an actual plumbing leak anywhere? If there isn't, it could be condensation, but another theory is that there's a leak at the connection (sink/toilet/bath) drain that causes the water to travel down the outside of the pipe and get trapped by the insulation. – DA01 Dec 16 '12 at 22:46


Insulation does not, by itself, cause condensation.

Insulation (in conjunction with other factors) prevents condensation.

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Umm, yes and no. Condensation occurs on surfaces that are cooler than the dew point of the surrounding air. Could be insulation, pipe, whatever. Insulation would typically keep it's surface from getting that cool, but it could happen. It can also trap moisture, lowering the dewpoint and causing condensation. But then one would have to ask where is this moisture coming from? – bcworkz Dec 18 '12 at 0:09

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