go into the attic & look for plumbing pipes,
hvac ducts and take some pics.

where is the stain on the ceiling?
near a bath fan or hvac supply?

pics?

best of luck.

Thanks for your reply! There is really only crawl space above there, so its difficult to get up and look around. It is near a fan and hvac. I did think maybe it's condensation coming back down through the fan? We haven't run heat or AC lately. Attached are a couple pictures, but its not wet right now, so you can't see the bubbling or the condensation. You can see in the picture the little piece of pealing paint on the right is from where I poked a hole in the bubble. The other split paint was already there although it may be related. It's not really stained, but there are a few little mold/mildew spots. You can see that in the pic too.

Here's a shot of the full ceiling.

just a guess...but it might be that the bath
fan doesn't have a back draft damper, isn't
vented, and is putting the moisture back
onto the ceiling on the attic side.

the moisture could collect on the duct & drip
onto the back of the sheetrock.

could be openings around the supply box & bath
fan in the sheetrock are oversized...

could be a lot of things, you can't tell from here.
you'll have to take a look, and post some pics.

y'all use the bath vent fan when you shower in this
bathroom?
use this bathroom often?

what your location?

best of luck.

We never shower in that bathroom. It's the upstairs hallway bathroom, which will be the kids' bathroom eventually, but we don't have children yet, so it doesn't get used. We don't run the exhaust usually either (since we're not using the bathroom), but I've run it for a few minutes the last few days, just to clear it out. I haven't noticed any wetness since I started doing that, but that could be a coincidence, since the wetness was coming and going anyway. I have checked it after we get ready for work in the master bathroom the last couple days, in case there is a leaking water pipe running over it or something, but it hasnt been wet, so doesnt seem to be from that.

We're in the mid-atlantic, so its just starting to get chilly out, but it was unseasonably warm the day I noticed the wetness (around 70 degrees, when it would normally be 50s and 60s). We havent been using heat or AC lately.

Climb up into your attic and look for wet spots of the roof material. You could have a leak in your roof. Did it rain within a day or so of you seeing the water. You will find wet insulation up there if there is a leak. Also, look for black areas around the leak. If they are there it could be mold. Don't mess with mold as it can kill you and it will!!!!! (NSA, I'm not threatening anyone... okay) You have to have it removed as it will continue to grow!!!!!!!!!!!!!!!!!!!! Big $$$$ but it has to be done.

see why I don't often offer wags...

sooner rather than later someone will have to
take a look up there.
see what is around that area, any signs of water damage
on attic side of sheetrock? on roof decking?
lack of insulation?

I'd better quit before I make more wrong guesses!
but let us know...I'm curious.

best of luck

No, it hadn't rained, Toolbelt68.

Thanks for your input everyone. Guess we'll have to get someone to climb around up in the crawl space to really figure out what we're dealing with. I tried to stick my head up into the attic opening, but you can't see over to that area. Someone is going to have to climb in there and crawl over. Who would you hire for this sort of thing? Just general handyman?

It's been dry whenever I've checked it the past few days, so I'm not feeling too pressed about it right now, but I'm guessing if we don't figure out what it is, it's going to come back eventually.

Since water does not run uphill the source has to be above the wet spots, right? What is above the wet spot? Maybe an Air conditioner unit, vent ducts for the bathroom exhaust fan, or a leak in the roof.

A lot of water has to set on the ceiling drywall before it leaks through. It could have taken days for it to happen. If the fan duct is not sealed properly then condensation could form but it would take an awful of water to soak through the drywall ceiling.

Air conditioners have a pan that collects the water that is removed from the air. If the pipe that removes that water from the pan is clogged then the overflow could be the source of the water.

If all you see up in the attic is insulation then IâÂÂd lay money you have a roof leak!!

IâÂÂd hire a local kid to climb around up there, but thatâÂÂs me. In this day and age you need to have them sign a release clause⦠lol.

A general handyman should be able to find the leak.

Hope that helpsâ¦. toolbelt

Since water does not run uphill the source has to be above the wet spots, right? What is above the wet spot? Maybe an Air conditioner unit, vent ducts for the bathroom exhaust fan, or a leak in the roof.

Water can also run sideways and down, if it hits something horizontal; it doesn't only drip straight down.

I agree--get a general handyman to help you find the leak. Then you can figure out what sort of treatment it needs, and whether the handyman can do it, or you need a roofer, a window guy, whatever.

Send him up there w/ a digital camera.

Good luck! Don't put it off--water is hugely damaging.