Mold and a Sick House Mold removal in homes with indoor moisture problems

Editor's Note: You can link to FAQs and articles by Thad Godish and others in our Mold Center.

Q. I have what I would consider a sick house. During the winter months (I live in ND) we had some condensation problems on our windows. All of them were covered with a black/green looking mold. We wiped this clean as often as possible and when spring arrived, I cleaned all the surfaces with a diluted bleach. We also had a condensation problem on one of our exterior walls. This caused mold to grow up about 2 feet on the interior wall. I have since had an Ultra Violet(UV) Air purifier installed. Prior to installation we had air sampling done as well as several surface cultures. The pre-installation sampling included higher levels of Cladosporium Species indoors than out and also Malbranchea 1. 0 Colony Forming Units (CFU), Pithomyces 1. 0 CFU, Epicoccum, 1. 0 CFU and Basidiomycete 1. 0 CFU were found indoors and not out. In the post installation test, the indoor quantity of Cladosporium was significantly less inside than out (From 400 CFU out to 68 CFU in). However, we again had species inside that were not detected outside. - Grant, North Dakota
A. Condensation on windows and occasionally walls is not uncommon in very cold winter climates such as those experienced in North Dakota and many parts of Canada.
Condensation is particularly a problem in houses that have older single pane windows or some of the earlier thermopane ones. It is also a problem in houses that have high indoor moisture generation rates from showering and the building site.
One can mostly avoid such problems by installing triple-pane windows and insuring that the shower area is well exhausted during and after showering. Site-generated moisture is a much more complex issue.
The fact that mold was found growing in the wall indicates that the walls don't have a vapor barrier or if it does it was not properly installed. It is the job of a vapor barrier to prevent water from passing into walls, hitting a cold surface and then condensing. In older houses it is usually cost-prohibitive to install a vapor barrier unless other renovation work is being done.
If you have mold growing in your wall, the best approach is to remove the interior wall covering and enter the cavity (not literally). If considerable decay is present, remove and replace affected timbers. If infestation does not involve decay, vacuum infested surfaces with a high-powered shop vac (at least 5 HP), brush with a stiff brush, and vacuum again. Then apply a mold inhibiting paint. To minimize exposure to you and other members of your family, take appropriate precautions including isolating the area, use polyethylene drop cloth, and respirator. Don't carry infested materials out without first wrapping them lest you spread mold spores around your house.
The ultra-violet air purifier will provide no benefit to you as it does not reduce one's exposure. It can kill mold spores. However, it does not matter whether mold spores are dead or alive when it comes to causing allergic symptoms or asthma attacks. Using a UV purifiers can alter air tests results when culturable-viable (culture media) sampling is conducted. Measured concentrations should be lower.
Cladosporium is a black mold and it commonly grows on condensate-affected window-related surfaces. Higher indoor concentrations indicate a source of infestation. Lower values of indoor mold after the installation of the UV purifier do not indicate that health-affecting mold levels no longer exist. It matters not whether mold spores are alive or dead when it comes to most mold-related health problems.