Most building codes for quite a while now have required air to be vented outside. Venting to the attic or to the space between floors, which used to be done, seems like a recipe for growing mold, especially in Florida. I know when we added venting to our home in MA over 20 years ago we had to vent to the outside.

The Florida makes an exception for those big, whole house exhaust fans but not for smaller one like in a bathroom or over a stove.

CHAPTER 15 EXHAUST SYSTEMS
| 2017 Florida Building Code - Residential, Sixth Edition | ICC premiumACCESS

The bathroom exhaust runs are very long. They go from near the front of the home all the to the back and up near the roof vents. The master run is just hanging in space a few feet below the vent. The guest run goes up into the vent. I suspect the master one once did but broke loose at some point. While the master exhaust run does have a low point (and a taped up junction between two sections of duct) right above the laundry ceiling, the oven vent pipe is also in the same area. As best as I can tell, the dryer vent is nearby but a bit too far away from the area in question to be responsible. We'll see what the roofer says on Wednesday but at this point, unless he finds something obvious, I'm thinking of floating the idea of replacing the gooseneck vents for the oven vent and also the dryer vent just in case (maybe changing the angle as well as others have recommended). Plus, as we're expecting a lot of rain today, I might go up in the attic again and sit there watching for drips (now that sounds like fun, eh?). One thing complicating all this is that there's a foot or more of blown-in insulation covering everything up there.
--
bc

Unfortunately the rain we're getting isn't heavy enough to trigger the problem (yet, anyway) but while I was up there looking around I decided that I really had to get over my trepidation at climbing deeper into the attic so I could reach the laundry ceiling area.

I took a broom with me to clear away the insulation so that I could see the other side of the laundry ceiling. I've attached some more pictures. The first is the oven vent from the outside. The second is the oven vent from the inside. Note the black stains along the beam above the red arrow and the strip of yellow sealant. The third is a closer view of that area and shows that the yellow sealant gets very thin right near the beam where the stains are. Finally, the fourth shows the attic side of the laundry ceiling and what looks like water stains centered around the seam in the ceiling drywall.

I suspect the thinness of the yellow sealant at the beam is probably responsible for the leak.

Comments?
--
bc

Some parts of that stain in pic 3 look to be pretty dark... mold?

I didn't think that the flake board was sealed to the rafter... maybe glued though.

You can pick up a moisture meter pretty cheap at Amazon or probably home depot/lowes. That would tell you if that would had picked up mosture or it was just some kind of discoloration that was on the original wood. You could also use it to poke at other suspect places.

https://www.amazon.com/General-Tools...s%2C415&sr=8-3

Yes, probably mold from being wet on and off over a long period. There's no such stains anywhere else up there. At this point I'm going to leave it to the roofer. Going up there isn't good for my health. The risk of falling or mistakenly stepping onto the ceiling rather than a beam, not to mention the coughing fits I have after trying to move that blown in insulation around. It's time to apply (the late Jerry) Pournelle's law. If you don't know what you're doing, hire someone who does. :)
--
bc

I met with the roofer this morning. He recommends replacing the vent with a modern, all one piece unit and re-shingling the area. He wasn't sure why that yellow sealant was used in that area. He said that's not usually done. Perhaps it was a previous attempt to stop the leak and not part of the original roof job. Anyway, we'll see how it goes.
--
bc