A mystery worthy of Ray Wohlfarth

DCContrarian

Maybe. I'll let you be the judge. It had me scratching my head for a while.

I got asked to look at an intermittent plumbing leak. House is one story with a full basement, and from time to there would be water on the floor of the basement. Looking up, the plywood subfloor above shows signs of water staining. There are two full bathrooms above the spot. They share a wall that runs north-south, one bathroom on the east side of the wall, one on the west side. The leak spot seems to be below the shared wall.

My first thought is that either the shower mixing valve is leaking in one of the baths, or water is getting behind the escutcheon of one of the valves and trickling down. So I take off both escutcheons and look down into the wall with my endoscope, but there doesn't seem to be any sign that water has been there. I run the showers for a while just to check, but don't see anything.

So now I inspect the shared wall. From north to south on that wall is the tub from the east bath, then the tub on the west bath, then the east sink and the east toilet. The west sink and west toilet are on a different wall so they're out. The east bath is eight feet long, there are six stud bays in the wall, and from north to south they are empty, east bath, west bath, empty, east sink supply and drain, toilet supply. The water supply comes up below the sink, the hot and cold go horizontally north to the two baths and the cold goes south to the toilet. The two tubs and the toilet have drains that go below the floor and join the stack, the sink drain runs north through the wall and joins the drain for the west tub. Got it?

The original plumber made nice big holes for everything, the ones for the sink are in the vanity and don't have escutcheons, so I'm able to get my endoscope in and look around. I inspect the bottom plate of each stud bay, and I find the one with signs of water is the empty one between the sink and the west tub. Aha! There are three pipes running through this bay from the sink to the west tub — hot, cold and drain.

The hot and cold are obviously intact. I suspect maybe the drain has a hole it in, like someone got it with a screw through the drywall or something. That might explain why this is an intermittent leak, if it's in the side of the pipe it might only leak when the flow is high. But I inspect the pipe and don't see anything. I run the water in the sink for about 20 minutes, try stopping the drain and letting it go all at once, but I can't get it to leak.

Then I realize what it must be. What did I see?

hot_rod

Around the tub spout on a tub shower installation, or the waste and overflow on the tub

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1806969#Comment_1806969

Nope. No leakage in the stud bay of either tub.

retiredguy

The sink overflow had a hole or leak in it and would leak when someone overfilled the sink to when the water would flow through that overflow.

dko

Saw condensation?

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1806977#Comment_1806977

Bingo. When I ran the showers with the escutcheons off, I saw condensation on the cold water pipes after about 20 minutes.

Remember I said, "The original plumber made nice big holes for everything, the ones for the sink are in the vanity and don't have escutcheons…"? That allows for a good exchange of air between the room and the wall. When the humidity in the bathroom is high that humid air gets into the wall and the cold pipe sweats. That middle bay is just where it happens to drip.

The reason it's intermittent is that conditions have to be just right, a combination of high humidity and cold water use.

I sealed all of the openings in the wall with spray foam. The basement is conditioned and nice and dry, the pipes don't sweat down there, so I didn't seal between the basement and the wall. I think that will fix it.

JUGHNE

Nursing home with wet floor in the dining room. RTU was directly above it…..has to be the source….right?

Wrong, everything above this wall/floor was dry. I was baffled until talking to the kitchen help and they said the floor at the cook's sink was always hot to the touch. It was almost 100 degrees on the floor in an air conditioned kitchen. The sink was over 50' from the water coming up thru the floor in the dining room.

Just about all the water lines in this 40 bed facility are above the ceiling. Except to that sink.

The H&C run down inside a wall about 6' from the sink which was on an outside wall, and it was obvious that the hot line was leaking.

I was able to cut the wall open and cap the hot line and later run hot water from another area thru the cabinets.

The water was following an electrical conduit trench to where all the risers came up in the boiler room.

The sink cabinet had been cooked for a long time as the particle board wood was all swelled up and the counter top was also swelling. The help told the head cook about this months ago but she never reported this.

Mad Dog_2

When all else fails, pour water around the outside of the tub or shower...hairline gaps....Silicone time..Mad Dog 🐕