Sustainable Construction Services recently completed a project in Cherokee County, Georgia involving mold in a crawlspace.  We thought it would be important for you to know the background and some details of the project so that if you own a home on a crawlspace or basement you can know what to look for and what steps to take.

The following picture is what we encountered when entering the crawlspace for the first time.  When we walked in there was a distinct musty odor and just looking around we could see that almost every square inch of wood was covered in black, grey and green mold.  It is important to note that this was an extreme case in that the building was still under construction.  The speed that the mold appeared and the amount of mold growth is very rare but shows that with just a little water and something to grow on mold will flourish.

This crawl space was designed the same way most traditional crawl spaces are designed in that it had a dirt floor and several vents in the walls to let fresh air into the space.  The vents are designed to let air blow in one side and out the other.  The problem with this design is that crawl spaces are victims of what is called the stack effect. 

The stack effect works similar to a chimney.  As the air in your fireplace heats up it becomes less dense and rises up and out of the chimney.  The fire then draws fresh air from your home to warm up and eventually this air will also rise up and out of the chimney. 

Throughout your home air is constantly moving.  It may be blown by your HVAC system or it may move because of changes in temperature and density.  As the less dense air in your home rises up into your attic and eventually out of the attic vents it draws fresh air into your home.  If you live on a crawl space some of the air being drawn into your home is coming from the crawl space.  Because of this the vents in your crawl space are not allowing air to flow in and out of the space but they are all drawing air in, which will eventually end up in your home. 

Since the crawl space is not performing as it was originally designed, the moisture in the air as well as any moisture coming from the ground or concrete foundation is essentially trapped in the crawl space.  This is the moisture that the mold will use to form. 

The fist step in the Cherokee County project was to get rid of the mold.  First the mold was treated with a cleaner that killed and removed the actual mold.  Once the mold had been cleaned a preventative spray was used to help prevent regrowth of the mold.

Now that the mold had been removed it was time to fix the original problem, the moisture in the crawl space. 

There are countless different ways to seal a crawl space.  The first step is to seal the crawl space off from outside air.  This can be done by adding concrete to the dirt floor or adding a vapor barrier to the dirt floor and walls.  The decision on what material to use is primarily based on how you are going to use your crawl space.  If you rarely to never use it a thinner, less expensive vapor barrier is probably the way to go.  If you use your crawl space for storage a thicker, more durable vapor barrier or even concrete would be a good fit.  When sealing the crawl space not only is the floor covered but generally the walls are covered with a vapor barrier or spray on insulation (which can act as a vapor barrier and help keep your energy costs down) and the outside air vents are closed and sealed off.

Once the crawl space has been sealed we recommend that you either introduce conditioned air into the area or add a dehumidifier.  This is an important step because as tight as we can seal a crawl space air is going to find a way in.  By introducing conditioned air from a HVAC system or adding a dehumidifier we will be able to control the moisture content in the air and ensure no future mold problems.

As you can see by the picture above, at the Cherokee County project we elected to add a moisture barrier.  Because of the size of the crawl space and the inaccessibility of the HVAC system we added two dehumidifiers to control the moisture content in the air.

Crawlspace design and mold can be serious problems to a home.  If you have a crawlspace you should seriously consider an encapsulation system including a vapor barrier and either conditioned air or a dehumidifier.  If you have a mold problem please contact us and get it taken care of before it begins to affect your health.