Causes Of Crawl Space Mold. 5 Issues That Can Cause You Mold Problems That You Should Be Alarmed About


Crawl Space Mold

Mold growth heavy enough to write in!

The cause of crawl space mold is simply moisture.   There are at least 5 different things that can cause you problems when concerning moisture in your crawl space.  All of these items can cause mold in your crawl space.  They can do it on their own, or then can all contribute to being the cause of mold in your crawl space.

  1.  Not getting water away from your house will cause crawl space mold:  If you are not properly getting the rain fun off from your gutter systems far enough away from your house, you are allowing that moisture into your crawl space.  Once that moisture is in the crawl, you now have a good environment for crawl space mold growth!  As a rule, you want to make sure you have down spout extensions that get water 4-6ft away from your house.  The standard 2ft down spout extension that the builder leaves you, does not come anywhere close to removing the water away from the house.  Explanation of why this is important: Think of the entire surface area of your roof.  All that area collects rain water and usually channels it down to just 4 or 5 down spouts.  Depending on how heavy the rain is, that could create huge amounts of water coming down to just 4 or 5 points.  Once the water makes it down the down spouts, water will pool around the block walls and footers of the crawl space. That water then works its way into the crawl.  When this happens, the over relative humidity of the crawl space begins to rise.

  2. Air ventilation in your crawl space can cause crawl space mold: Over 90% of the homes that have crawl spaces, also have crawl space vents.  They have built in crawl space vents since they have been building homes with crawls.  (Recently, builder best practices seem to be going away from having vents)  With outdoor vents used in the majority of older homes, you get and eb and flow of air into the crawl space.  Outside air constantly changes.  It can be very dry air one day, then very heavy wet air the next.  Moisture always travels to were it is dry.  Think of it this way.  When you drop a drop of water on a paper town, the water spreads out.  So if you have humid air outside, it will get sucked into the crawl space area if that air is dryer.  When this happens in the summer, you then get relative humidity to rise over 60% in the crawl space, you then have an environment that is ripe for crawl space mold growth.

  3. Condensation issues with your HVAC duct work will cause crawl space mold:   This issue usually happens when you have other contributing factors that have raised the relative humidity levels.  As you run your air conditioning unit, that cold air runs through the duct work.  The cooler duct work starts to condensate as the moist warmer air from the crawl hits it.  You then get your version of a mini rain forest.  Duct work condensates, water droplets drop onto the ground below.  (or vapor barrier).  This then helps raise the relative humidity levels even higher, which then makes the condensation levels higher.

  4. Vapor Barrier:  Most homes that have crawl spaces, seem to have at least some fashion of a vapor barrier.  Vapor barriers job is simple to do as the name implies.  Trap moisture from rising from the ground into the crawl space.  When you do not have or do not have a properly install vapor barrier, you can have a cause of crawl space mold.
  5. HVAC Drip Lines will cause crawl space mold:  There was a time, when builders would let the drip line from the HVAC system just empty into the crawl space.  While that isn’t an acceptable practice any more, we still see some older homes where this was done.  The HVAC systems collects a large amount of moisture from the air in your home.  The drip line is how it gets rid that moisture.  If it does lets it “drip” into the crawl space, you just created a large unnecessary source of moisture for your crawl!

Any one of these issues can cause mold in your crawl space.  Often times, they all work together to create high levels of relative humidity.  Once that relative humidity is above 60%, you get an environment that is ripe for mold growth.  If you want to avoid mold in your crawl space, you need to try and limits the things mentioned above.  For more information on mold and mold remediation, visit our site

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