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.