Damp on the ceiling of the flat downstairs looks like a leak - what should I do?

Question

A couple of days ago the downstairs neighbour knocked to say he was seeing some damp on the ceiling of his bathroom that might indicate a leak coming from my flat, so I went down to look and it does look suspiciously like leak damage (one corner of the room has black mould in it, about an inch diameter, with brown tide marks radiating out from there). His bathroom is directly below my bathroom (I live in a relatively modern building, about 8 years old, so his flat is an identical clone of mine in terms of layout).

There is absolutely no sign of a leak in my bathroom (no damp or puddles on the floor or up the walls) so my question is where do I start? I have read that water often travels a fair distance before pooling at the lowest point, and my bathroom is an integrated unit which has drywall on one wall but the rest of it is basically floor to ceiling tiles - if possible I would like to avoid ripping out and breaking all my tiles on a wild goose chase.

Questions:

• does it make sense to cut a peep hole in the drywall ceiling of the flat below, before trying to rip out tiles from my bathroom?
• what is the most likely culprit? I have read in several places that the wax seal on the toilet is a suspect - is it possible for this to be leaking only into the downstairs ceiling, and not outwards into my bathroom as well?
• any suggestions for troubleshooting and figuring out where the leak is, without pulling out the entire bathroom?

Thanks!

Answer 1

Sounds like a Wax seal issue to me, it would only leak when you flush, and would certainly drip through openings in the floor or tiles. They are only good for a limited time, but good news they are only about $7 and easy to change if you have a helper.

Loosen bolts, lift toilet, have partner remove and replace seal, plop down toilet, sit on it, then tighten the bolts without breaking the toilet. Since it's a rental, Tell your landlord to credit you $100 and everyone wins.

Answer 2

I agree with Scott DV, absolutely start with the toilet seal. But, don't touch (cut, harm or destroy) the drywall or whatever in the downstairs bath. If the toilet seal stops any further problems. Drywall like anything else can dry out in a week & be perfectly fine. All that you might offer to do down there is priming & painting.