Plumbing Leak in Duplex

[Art Maydan]

My duplex has water leaking through the downstairs bathroom ceiling (link). Upstairs, the toilet is directly above this. I had a contractor come before. He lifted up the upstairs toilet and there was water around the pipe. He replaced the wax seal and caulked the empty space around it.

http://tinypic.com/r/2zdyhjm/9

http://tinypic.com/r/23rmja9/9

The issue didn't go away and I had another contractor come. He confirmed it's the toilet and said it's possible the first contractor did a bad job and if he re-seals the toilet, that will be enough. He says that might not be the source though and we have to open the wall to see what the issue is.

Judging by the pictures, is anyone here able to get an idea of what's going on? Do you think I need to open the wall? This guy said he'd open the wall and do an inspection for $200. That's not counting actually repairing it and he said I'd need to hire someone else to repair the drywall once the water issue is fixed. Does that sound right or should I be able to find someone who can quote me more precisely and do the entire job, drywall included?

[Michael Boyer]

Here's another angle if the toilet repair does not fix it. Not sure if you have looked at a possible sweating cold pipe in the walls. For example, a cold water supply pipe above that vent might have warm moist bathroom air from the downstairs shower/bath migrate and condense on the cold surface causing a drip drop minor leak. Hence the parallel water spots.

Just from what I see (the small, parallel water marks) this could be consistent with a cold water supply pipe running vertically above the lower bath (in the cavity) and warm moist air contacting it. For that matter, the toilet can sweat, too, explaining some of that water the plumber saw.

I had this happen once. I insulated the cold water pipe (with the flexible black kind with adhesive strip) and blocked the passage for warm moist air to get into the wall cavity. So far so good. I was able to do it from an adjoining unfinished laundry, so I did not have to open the wall.

Making sure the lower and upper bath have good ventilation (powerful, working exhaust fan). That might help. Or you could try a dehumidifier, too. 

But the larger fix may be something like a mixing valve or insulating those cold pipes or adding ventilation. It would probably not hurt to look at the cause now.

Best of luck.