How to pinpoint the source of household mold.

January 27, 2006 1:57 PM

My father has a problem with mold and humidity in his house. It grows copiously on the exterior walls of exactly one bedroom. Condensation appears on the windows, to the extent that there is a puddle of water on the window sill every morning; and this is a year long phenomenon. (Interestingly, the area around the windows does not get moldy. )The humidity in this room is literally palpable. We pulled up the carpet today, but it was always moist to the touch, towels don't dry, etc. The walls have to be cleaned with bleach every month or two. There is an adjoining bathroom, and we've tried leaving the windows open but it seems to have no effect. In any case, there is another bathroom in the house which in never ventilated and there is practically no mold. At this point we need to pinpoint the source of the humidity, and why it is only found in this room. Any ideas? If you need more info just ask.
posted by zorro astor to home & garden (12 comments total)

could it be coming up through the foundation? i lived in an apartment where water leaked up through the floor.
posted by clarahamster at 2:20 PM on January 27, 2006

Does the plumbing go through that room ? Maybe there is a broken / leaky pipe in there. You might also try to peek (if possible) above that ceiling...could be a leaky roof. Just a couple of thoughts.
posted by lobstah at 2:20 PM on January 27, 2006

Check for plumbing leaks in the wall adjoining the bathroom and also in the cellar or crawl space below. In my opinion, the moisture (and there must be a lot of it) is coming from below, somehow. If you can scan the floor of that room from below and it is dry, well, I'm wrong. But water vapor does tend to move vertically.
posted by Hobgoblin at 2:27 PM on January 27, 2006

Are the rest of the house's windows double-glaze or two layer, and just this room has single layer of glass? That would do it.

Is it a bedroom? Breath is laden with water, and bedrooms generally have a personbreathing in them for 8 hours a night. (Is the door closed at night?)

Does it face somewhere cold that gets no sun to warm it up?
posted by -harlequin- at 2:37 PM on January 27, 2006

Actually, we've been thinking that the moisture might be coming from the ground. Would ground moisture actually make the air in the room humid, though? When you walk into the room you can literally feel the humidity. thanks for the comments so far.
posted by zorro astor at 2:44 PM on January 27, 2006

Without some details regarding location of the house (from your profile, Astoria, NY?), age, and its construction, only general advice is possible. But assuming its a standard frame house of relatively modern vintage, here are some starters.

To discover the cause of the problem, and permanently remedy the situation, you have to open up that wall, by removing the sheet rock (also known as dry wall), which is probably softened and degraded by all that moisture, anyway. It's likely there is some outside leak, either in the roof system, or the wall sheathing system, and water has made its way inside the wall, wetting any insulation there. Even a small amount of trapped water will take a long time to work it's way through drywall to evaporate (particularly since, in a lot of newer energy efficient houses, there is usually a plastic sheet vapor barrier under the outside siding holding it in), and in the meantime, additional seepage can occur to recharge it. Moreover, once the insulation is wet, it provides a home and moisture and enough warmth for colony insects such as carpenter ants to flourish. I once opened up a wall for a friend who thought he had a small roof leak, only to find soaked insulation and a 2 foot diameter nest of ant egg capsule, with probably more than 200,000 egg capsules.

You might first want to get up in the attic, and look carefully at the underside of the roof and the joists and soffit area along the top of the wall, checking for any evidence of leaks or water damage coming down. You may also find pipes near that area, which could be leaking.

From the outside of the house, you could carefully examine the lower sections of the roof, and especially the gutter system, if any in that area, looking for ways in which water could leak from, or overflow the gutters, making its way into the soffit, and down inside the wall. Here's a link to a This Old House segment with some info about reparing rotted soffits that may be of interest.

But in any case, if the insulation inside the wall is wet, to fix it, you are pretty much going to have to remove the existing sheet rock. With the wall open, the source of the problem is probably going to be obvious.
posted by paulsc at 2:46 PM on January 27, 2006

I'm livng in Tampa now, and the house is a concrete block biulding, probably built in the late 60s. If you've been to Florida you wil know what type of house I'm talking about. Your comments are helpful, but it still seems strange that such strong and diffuse humidity would not have already shown up materially in something visibly rotting. (Of course it could be rotting in the walls, as one may extrapolate from your post.) Will investigate further. Thanks.
posted by zorro astor at 2:58 PM on January 27, 2006

I live in Jacksonville, and know that type of construction. A lot of those style homes have metal roofs, and if your dad's does, it's quite possible he has minor leakage around the nails used to attach the metal panels, or even more basic problems, like insufficient pitch or venting. The metal panels have raised channels which are supposed to vent air from under the eaves up to roof peak, and create a means of venting any water vapor, but in a lot of cases, poor installation makes a system that doesn't work.

In any case, if he's ever gotten any water into the insulation by any route, and considering the house is in Tampa, there's about a 75% chance he's got a carpenter ant infestation in there, too. Once the colony gets going, they maintain moisture on the egg capsules by regurgitating moisture, food and feces in the nest, and it's like you have an invisible low volume, but constant water pump going in there. Amazing how much water they'll drag in to keep the brood going.
posted by paulsc at 3:26 PM on January 27, 2006

Probably not specific to your problem, but I've been hearing a lot of PSAs on the radio lately about how localized humidity and puddling moisure can be signs of a Carbon Monoxide problem in the house. Where is the water heater in relation to the room? Are there any other gas or propane appliances nearby?
Like I say, probably not relevant to your house but I thought I'd mention it for the benefit of future archive searches.
posted by BigLankyBastard at 9:01 PM on January 27, 2006

A long shot, but make sure that your clothes dryer (if you have one) is vented to the outside and the vent is not clogged. I've seen some truly unbelievable vent installations (including, yes, venting into a wall cavity) and vent lines, particularly those flexible shiny ones, can get clogged with lint. All that water in the clothes has to go somewhere.

If the adjacent bathroom has a vent fan, check it too. Easy check is to find the vent on the exterior wall where the air should be coming out (the bathroom one may be routed through the roof so not so easy then) and see if in fact you feel a breeze when the fan/dryer is running.

One observation: if you live in Tampa, I would think that the windows you mentioned would not get cold enough to condense water, even at night. If there's puddling, I would at least consider that the windows might be leaking. Are they a different kind of window from those in the rest of the house? Do they face in the direction of the prevailing winds?

Note that paulsc's ideas are more likely, but you never know.
posted by skyscraper at 9:09 PM on January 27, 2006

Hey, update this when you find out, would you?

I'm saying plumbing leak, improper venting, roof leak--in that order. Definitely suspect the plumbing leak. I had similar symptoms (but to a lesser degree) with a pinhole leak in a water pipe under the slab. Fixing it was a royal pain, as you might suspect.
posted by RikiTikiTavi at 9:57 PM on January 27, 2006

There are no appliances or such anywhere near the room. I doubt it's a plumbing issue because the room is a corner room and the problem is on the exterior walls. Will need to check out the ceiling next. If nothing there, in a couple of weeks we're going to dig a ditch down to the foundation and tar is so as to keep water from leeching in. In the meantime, removing the carpet seems to be having a good effect.
posted by zorro astor at 2:16 PM on January 28, 2006