When renovating a house once, I had a persistent leak that occurred after every heavy rain. The leak through the kitchen wall, oddly enough, and there were no signs of water in the attic.

I knew there was a plumbing vent stack in the area, so we removed the drywall and sure enough, the vent pipe was the source of the problem. It turns out that the plumber had not tightened a connection, and rain water had been seeping out of that connection. In other words, the rain water entered the pipe at the roof and seeped out of the pipe at a loose connection behind the wall.

To diagnose the problem, the plumber got up on the roof with a garden hose and poured water down the vent pipe!

The plumber said this was the first time he had ever seen this happen. Next time, I'm going to be sure that all connections are tightened before I close up the walls.

Former builder and instructor of "Save Time and Money in Home Remodeling" cont. ed. course at Emory University