The Weather Inside Is Frightful
November 20, 2009 11:40 AM   Subscribe

Mystery water dripping from the ceiling in the late night. No rain, so no leaking roof. No upstairs neighbors, so no one else to blame. Is this the Rising Damp the Britcom is named after or does my apartment need an exorcism or what?

I've been fairly satisfied with my poorly-insulated apartment in a single-story triplex for the 4 years I've lived here. The climate is very moderate in San Luis Obispo, very rarely over 90F in summer or below freezing in winter. I'd often noticed the walls get very warm on warm days, but at night, I sleep quite well in a cool - almost cold - room. I run the wall heater less than 30 nights a year (and the gas is included in the rent).

The last week was the first time it got near 40F at night this season, and I noticed something strange; the walls weren't just cold, they were damp. And with my bed in a corner with no headboard, that dampness started seeping into my pillows. But it always dried out when the sun came out. Then last night, I was awakened at 4AM by a drip on my forehead...from the plain white painted ceiling where droplets were visibly forming all over the place! It was supposed to rain later today, so I looked outside where it was dry as a bone; there was dew on the window... on the inside! WTF!

It was about 37F outside; I turned on the heater, curled up under the covers, and by morning, it had pretty much dried out. Only some brownish droplet-shaped spots on the ceiling remained as evidence I hadn't hallucinated the whole thing. The only source of indoors moisture is a very slow drip in the shower, but the wet was evenly spread throughout the small (3 rooms, 450 square feet) area. Does this have something to do with the meteorological term 'dewpoint'? I may have stumbled onto a solution... warm it up... but why did this happen now and never before in four full winters here?
posted by oneswellfoop to Home & Garden (9 answers total)
I don't know why it hasn't happened before, but I theorize that you had very high humidity in your apartment that day (took a long steamy shower plus ran the dishwasher and did laundry or something) and it condensed on cold surfaces like your ceiling that night when the mercury dropped.

It rains inside my kitchen in winter, sometimes, here in San Francisco: I have a skylight that's evidently not sufficiently insulated even for our mild winters, and if I run the dishwasher in the evening the steam it produces during drying drifts up into the skylight and condenses at night. Then I hear drops hitting the floor (surprisingly loudly!) in the middle of the night.
posted by Quietgal at 12:09 PM on November 20, 2009

It sounds as if the humidity in your house is especially high, and water is condensing on the walls and windows when their temperature drops. Is the house close to a body of water? Is there any reason the water table would be especially high this year? Lots of rain recently? Have you been cooking a lot of soup or pasta? Is the house built from concrete or other masonry?
posted by jon1270 at 12:16 PM on November 20, 2009

This does sound like dewpoint to me, but I'm not a meteorologist. And yes, warming things up will help. It's like a large version of the fog on the inside car windshield, or the water condensing on the outside of a cold glass.

Three factoids:
1. you've noticed the walls are warm on warm days. i.e. not a lot of insulation, thus cold walls on cold days.
2. People are inherently moist - we sweat (even when we don't notice it) and have very damp breath; we're the source of the fog on the inside of the windshield.
3. Warm air holds more moisture than cold air. That link about the sweating water glass should help.

In the early evening, the air outside cools down. The outside air may have been more humid during the day, but reaches a dewpoint, and the grass gets damp. Inside, you're keeping it just a bit warmer (presence of human body, cooking, shelter slows down temperature swings, etc), but your walls aren't well insulated and are coolig down pretty fast as the sun sets and the outside air gets colder. Eventually, you get to the dew point: there's a certain amount of water in the indoor air (humidity) and when the air cools to a temperature that is can no longer contain all that water, the water condenses on cold objects (like a glass of ice water in summer) such as your walls. Basically, if there's dew outside, and your apartment is set up for such a temperate climate that it's pretty much the same inside and out, there'll be dew inside.

A nice hypothesis, totally unproven.

I will add, though, that in my house, the fog after a hot shower, isn't contained to the mirror but condenses all over the walls. And yes, such events often leach brown/orange color out of the drywall, especially if there were smokers in the house previously, which can be pretty gross if it continues.
posted by aimedwander at 12:26 PM on November 20, 2009 [1 favorite]

Where is your water heater housed? This happened to me and it turned out to be the water heater, which is stored in the attic. It had developed a leak, and the drainpipe designed to carry out the water was badly made and also leaking.
posted by scarabic at 12:29 PM on November 20, 2009

aimedwander has it right. The key fact is that the walls are generally damp. It's not a point source and it goes away when the rooms warm up. Leaks don't do this.

If it's not common, you probably just had a batch of unusually damp air and unsually cold temps. It's likely to remain uncomon.
posted by rusty at 1:52 PM on November 20, 2009

This all makes good sense but still leaves the mystery of how it got extra humid inside my apartment... the water heater for all 3 triplex units is in a little shed out back... I actually missed taking a shower the day before the big drip (and the shower leak wasn't any worse than usual)... I have done no unusually moisture-heavy activities lately (except my sinuses are draining and that's snot, not water) and the apartment is well ventilated with a window fan with a thermostat that turns off automatically...

I did notice the bathroom near the shower was still wet when the rest of the apartment had dried out... maybe that leak is having a greater effect than I thought... and cooler weather means the fan shuts off earlier... hmm... going to keep the bathroom door shut tonight; see if I end up with a swamp in there while the rest of the place stays dry.
posted by oneswellfoop at 2:08 PM on November 20, 2009

Moist air could be coming in from another apartment, or something like the drywall could've gotten wet and it's slowly evaporating.
posted by electroboy at 2:32 PM on November 20, 2009

The shower drip concerns me. Take a look at the nozzle and see if there is any rotting around the bottom, where it meets the surrounding material. It may be leaking into your crawl space (have the owner look under the units) As it evaporates upward, it could be saturating the wallboard and causing an increase of humidity inside your triplex.
posted by Acacia at 12:01 AM on November 21, 2009

update: with bathroom door closed, the rest of the apartment stayed dry but the bathroom was experiencing a full monsoon @2AM... it appears the leak/drip in the shower, while not appearing different, was outputting more HOT water, upsetting the delicate ecological balance... Local Warming in Action... so it's time to get the landlord to call Joe the Plumber (no, not the political hack, we have a REAL plumber named Joe)...
posted by oneswellfoop at 1:03 PM on November 21, 2009

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