Crawl Space, Mold Problem

Old 08-14-03, 01:58 PM
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Crawl Space, Mold Problem

I have a 2000 sq ft house on a 3 ft crawl space. Recently, I have noticed a stale musty odor inside the house. I inspected the crawl space and found the following: 3 areas with standing water (1/4” deep and about 1ft dia) and what looks like white mold on many of the floor joist. I also found many of the items I store under the house contain mold.

The dirt floor is covered with plastic sheeting and appears to be in good condition. I could not find any leaks or a obvious water source. The crawl space is well vented on each side of the house. What is the best approach to remove the mold? My wife is complaining about her health. I am considering a dehumidifier in the crawl space. Is this the right approach? What size and model?

Need some help.

Old 08-15-03, 07:15 AM
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Where are you located?

In some climates, crawl spaces should not be ventilated during hot, humid weather (July and August around these parts). Whenever the average temperature and relative humidity of the air outside the house exceeds that located in the crawlspace, the space should be sealed from outside air infiltration, otherwise the humidity with condense insode the basement, prolly the source of the pulldes you are seeing on your vapor barrier.

When this humid weather finally breaks, and the dew point finally drops below the temperature of yoru crawlspace, consider running a fan to pull out the moist air beneath your house and allow drier air to enter through your crawlspace vents. When it gets humid again, seal up the crawlspace.
Old 08-15-03, 07:49 AM
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You can kill the mildew with a mixture of bleach 25% in water. On the beams and such, just spray it on and leave it. It will remove the color from desired items, otherwise. Standing water is normally the result of water running up under the house somehow. Check your downspouts, grading, and general water flow on your property to avoid water draining toward the dwelling.

Storing things of value in dark, humid areas can invite mildew unless they are cleaned prior to storage and draped or otherwise protected from the high humidity and the presence of mildew spores.

A stale, musty odor inside the house might indicate a source of air from the crawlspace into the house. Some of these may be openings in the HVAC ducting under the house, access ports to the crawlspace from the living space. Normally, the vapor barrier would keep the moisture levels down and prevent intrusion of the moisture into the house. Other sources of musty smells in the house are hidden leaks under sinks, vanities, and in walls where air conditioning equipment drains are blocked. If you have air conditioning, there may be some benefit to checking the filters and drain pans for cleanliness.

Unless the crawlspace is sealed, it seems that a dehumidifier would be of little value. You could improve the flow of air under the house by the use of a fan to pull air through the crawlspace. There are fans designed and sold for this purpose. They draw little power and move surprising amounts of air. There is considerable controversy about forced ventilation of crawlspaces as well as ventilation of crawlspaces at all.

If your wife feels ill, perhaps she should visit a physician to see what ails her.

Hope this helps.
Old 08-15-03, 09:30 AM
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I live in Atlanta and the rainfall this year has been incredible. I think I will try the air circulation idea. This seems to be the low cost approach and it may achieve the desired effects. Will this require a special vent fan, or will any high velocity fan move the air sufficiently.

Thanks for responses.
Old 08-15-03, 10:51 AM
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In Atlanta (warm/hot and humid), you are prolly better off NOT ventilating the crawlspace.

If you ventilate the crawlspace with outside air that has a dewpoint higher than the ambient temp inside the crawlspace, you will get condensation forming on every surface in the basement that is cooler than the dewpoint of the outside air. Any HVAC ducts that run through the crawlspace will be especially effective at forming condensation due to the cool temps of the air circulating inside them.

Many building codes in warm/hot humid climates have been changed recently to require that crawlspaces remain unventilated. The cadilac solution to this problem in new construction is to discharge small amount of cool, air conditioned air into the crawlspace to help keep it dry during warm/hot humid weather conditions. See the info at this link:

If it were my house, in order to reduce the humidity and moisture in the crawlspace, I'd seal it up and run a very large dehumidifer down there until the fall brings cooler and dryer weather, at which point I'd open it up again.

The spraying of bleach solution recommended above will be effective at killing any mold/mildew that is currently growing.
Old 08-15-03, 11:00 AM
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Received 0 Upvotes on 0 Posts Towards the bottom of this brief it discusses Crawl Spaces and what to do if you choose to vent this area or not.

First you must identify the source of the moisture before you can address the problem. Based on the information you gave, it is more than likely that the plastic on the floor is not sealed and it allowed water to bypass it. Tape the seams of the plastic to avoid water from accumulating on top of the plastic again.

Next, when the air-conditioning has been in use for some time, go into the crawl space and feel the subflooring or ceiling of the crawl space. If the temperature of the subflooring is much cooler than the rest of the crawl space, you have a problem. If the subflooring is cool and damp, you have a bigger problem. If condensation is present, you have a severe problem. I do believe you have a severe problem based on the information you gave and it would account for the white mold on your floor joists.

The severity of your problem is probably a direct result of a combination of factors and not just one. For example, if you tape the seams of the plastic on the floor, the problem will be lessened dramatically. Basically all that does is reduce or eliminate a source of the problem.

Since warm air condenses on cooler surfaces, there are several ways of addressing it where it will reduce or eliminate another source of the problem. Utilizing a high velocity fan does in no way address a source of the problem. In fact in my opinion all it will do is aggrevate the problem.

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