Hallway ceiling moldy

9 days ago

We've been having a problem with light splotchy mold appearing on the ceiling nd the uppermost 1 foot or so of the walls in the central hallway of our house. The strangest thing about it is that after living here for ten years, this year is the first time it has happened and I can't figure out why it has appeared this year and not before.

More details:

The house was built in 1972, located in the northern 'burbs of Atlanta, and has slab hardwood floors throughout.

This isn't a large hallway, no more than 40 inches wide, L-shaped with about 16 feet the long way and about 4 feet the short way, 8-foot ceiling. It's in the middle of the bedroom-end of the house, with three bedrooms around the long end and a full bath off the end of the L, and the L-end connects to a short hall-stub that joins with the living room, wet-bar, door to basement, and foyer.

The hallway has a pull-down door for the attic at the long end, and then just after that as you move toward the L there is a full-house fan, which has metal louvers that stay shut unless the fan is running, and it only gets run on exceptionally rare occasions- basically we only run it if we need to clear smoke (kitchen or fireplace oopsies) or an odor from the house. There is a linen closet on the long end and there is a small closet on the L that is mainly used for cleaning supplies.

The bedrooms: only one (master) is inhabited as our family consists of two humans and two cats. One of the other bedrooms is basically just a storage-space/music room and the other is supposed to be a guest-room but is also where the litter boxes live so nobody has slept in in for several years. That room does have an air-filter

Ventilation: The house has central air conditioning. All the vents and return-registers are down low, just above baseboard level. There are no fresh-air vents in the hallway but it does have one return-register about halfway along the long end, on the side that doesn't have the L, and it's double-sided so it also serves the bedroom on the other side of the wall. None of the doors to the hallway are ever closed for very long, the bedroom doors almost never and the bathroom door not for longer than it takes to have a shower, which happens no more than once a day. Both bathrooms have fairly recent fans that do a great job, we run them for about twenty minutes after showering and there is no mold in the bathrooms. None anywhere else either for that matter.

Moisture: no intrusion that I know of, and the roof is only three years old and doing a great job. The attic has louver-vents at each end and I have never seen any sign of mold in the attic. This is a humid region, but again, no problems until this year, not even when we DID have a leak before the roof was replaced.

And again, what's the difference that made the mold appear this year and not before?

After some attempts at cleaning it I can see that once the problem gets solved I'll need to repaint the ceiling and walls, but obviously I don't want to do that UNTIL I know the problem has been solved.

What seems like the best idea is to install a ceiling-fan in the hallway, but that also feels like a 'band-aid' because it doesn't address whatever changed to cause the mold to grow.

Anybody have any ideas?

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Comments (5)

Sigrid
9 days ago
Something went wrong and you need to figure out what. I did a quick Google of the humidity records in the Atlanta area and nothing stands out as special this year, which suggests it's your house, not the weather. I did a very quick look, you might do a deeper dive and discover it's the weather, but I'm pretty sure it isn't.

So, what could be going wrong? A tiny leak in plumbing or the roof? A vent got plugged? Screen or filter got clogged? It's worth noting that water runs downhill and tends to travel along structural elements, meaning that a leak in the peak of your roof might appear in a wall, downhill from the actual source. I had a bathroom with an unlevel floor and all problems showed up as water under the sink, even if the actual source was on the other side of the room.

Humidity meters are cheap, although the cheapest ones are not very effective. A bunch of them might help find the source, although a careful inspection of attic, crawl spaces and other very awkward spaces is in order. Check things out at different times --- when it's raining, when someone's showering, etc. I had an odd water-in-the-basement problem and when I crawled under the porch (a very awkward space to access) on a day when it was pouring, the mystery was solved. The downspout had a leak and water was pouring onto the foundation right at the spot where the water came through.
the_veg
Original Author
9 days ago
Thanks Sigrid and we've actually had a very dry summer this year at least in terms of precipitation.
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Clyde Kalvin
8 days ago
You need to get a hygrometer and check what the humidity is in your home. Dry as far as precipitation is different then high humidity.
PRO
Leak Detection Los Angeles
2 days ago
Since your summer was dry, I would want to rule out a slow hidden leak before assuming it is just humidity. Take a look in the attic right above that hallway after a rain and check for damp insulation or stains on the roof deck. A cheap pin moisture meter pressed against the ceiling will also tell you if the drywall is still actively wet. If both come back clean, then it is just surface mildew and the humidity fix will do the trick.
3onthetree
2 days ago
Would need to see pictures to see the extent. A water leak most likely shows on the ceiling, not the walls, and has a very distinct pattern compared to being caused from moisture.

It isn't important about the rooms on the hallway, but the attic. Like whether the HVAC unit and supply ducts are there (first said slab, but also basement), whether you have storage, whether you have enough insulation, whether you have enough passive attic ventilation, whether the bath exhausts discharge outside. Also unclear description about return vents (reads as only 1 but a transfer grille).