There are literally millions of mold spores floating around in the air all the time and everywhere. Indoor and outdoor air both contain enough spores for a mold colony to begin growing within two days under the right conditions. So mold is definitely contagious.

     An air filtration using a HEPA filter can be used to reduce the level of mold spores in indoor air. A UV-light in an air conditioning air handler is another alternative that, while useful for killing bacteria in the air, is only minimally effective killing mold spores. Even with a HEPA filter in place, air infiltration in a home will allow a steady flow of spores into your home. A “mold house” near you will put more mold spores in the air and, if the breeze is blowing your way, may temporarily elevate the mold spore count in the outdoor air around your home. But, even without a mold-infested house nearby, there are already more than enough spores floating around to start  mold growth inside your home.

    The rare exception occurs when you share a common wall with a neighbor that has an ongoing moisture intrusion problem, such as with a townhouse or condominium. We came across an example of this a few days ago, where a adjoining townhouse garage had a long-term roof failure (see photo below) and mold was coming through the shared wall between the two garages. A plumbing leak in a multistory condo can also spread mold into the walls below, especially if it is a slow leak with no drips or puddling evidence. But both these examples are based on moisture or high humidity from an adjacent property migrating to your home.

    So the key to eliminating the possibility of mold growth in your home is not related to a neighbor’s mold problems. Mold needs three things to begin growing: an organic food source, warm temperature and moisture. Take away any one of those three requirements and mold won’t grow, but the last one that is by far the easiest to control. Keeping the relative humidity of your indoor air below 60% is your single, best preventative for mold, according to the U.S. Environmental Protection Agency (EPA). They further recommend taking it down to 30% to 50% for assured mold prevention.        If your hygrometer has a 68% reading like the one above, it’s time to dehumidify the air. Roof leaks, plumbing leaks, and any other moisture intrusion in the home should be dried-out quickly when discovered, too.

     A central air conditioning system reduces humidity as it cools the air when the system is working properly, and a dehumidifier is another way to remove air moisture. Some new a/c thermostats also monitor indoor humidity and can be set to maintain a specific humidity level. Another alternative is a humidistat, which activates the a/c system as necessary to maintain a desired humidity level. 

    But if you want a cheap way to monitor your indoor humidity, we suggest getting an analog hygrometer. The one shown below costs less than $5 on Amazon, and can also be purchased at many hardware and home improvement stores. A brass case and fancy design costs more, but the $5 one works just fine.

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Here’s links to a collection of our other blog posts about MOLD, LEAD AND OTHER CONTAMINANTS:

• Should I buy a house with mold?  

• Why do new homes have more moisture and mold problems than older houses?

• Can infrared thermal imaging find mold behind a wall? 

• What is the right humidity level in a mobile home?

• Who can clean up mold found during a home inspection in Florida?

• How do I look for and find mold in my mobile home? 

• How can I tell if there is asbestos in a house?

• How can I prevent mold in my Florida winter home when I'm gone for the summer? 

• Should I use bleach to clean up mold? 

• What are those powdery white areas on my brick walls?

• What should I do if mold is found during a home inspection?

   Visit our MOLD, LEAD AND OTHER CONTAMINATES page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.