Relative Humidity means how full of water the air is relative to the maximum amount of water it can hold at a given temperature. When RH is at 100%, the air can not hold any more water and must give up its moisture. This simply means that it will either rain or it will come out on surfaces as condensation.
When warm humid air enters a crawl space, if the crawl space air was colder than the crawl space surfaces, it would rain in the crawl space. But that is never the case. The source of the cold is the earth and the source of the warmth is the air coming in from the vents, so the surfaces in your crawl space are always colder than the air in a crawl space.
So on a summer day, we get condensation, which means our crawl space walls get wet. Our air ducts get wet, especially if we have the air conditioning on because the ducts are cold. Our cold water pipes get wet. And as you can see here, the porous concrete gets wet.
There is a direct correlation between relative humidity and wood moisture content. Wood in a damp environment will become damp itself - damp wood rots and mold grows on it.
Our floor joists, girders, sill plates and insulation get wet with condensation. As the insulation gets wet, it gets heavy and falls to the crawl space floor. All these wet surfaces in a crawl space will eventually have to dry to somewhere. They dry into the crawl space air over the next weeks and months - and meanwhile, mold and wood-destroying fungi are having a party, eating your house.
Fiberglass floor insulation and moisture: a very bad combination!
Mold grows on insulation because it has some organic material in the resin used to set the fibers. When fiberglass insulation is just a little damp, it loses a whole LOT of its insulation value.
The next stop on our crawl space mold tour is the wooden subfloor joists. These joists are often the first place that you see mold growth because of the air from outside is being drawn up through the rest of the house due to air pressure.
This home had a 6 mil polyethylene ground cover. But, because it had holes in it and it wasn't sealed at the perimeter up the walls. For a vapor barrier to be effective in the long term, it must be durable. In this picture, you can see where water is sitting on top of the barrier and will allow mold growth.
In this album, you can join the Healthy Spaces team in a tour of an Owensboro, KY crawl space suffering from mold and high humidity. Here at Healthy Spaces, we believe that education on mold and how it can affect your living environment is essential for homeowners. Your home is one building and it operates as a system. You can't have one part of the building that is sick and another part that is healthy.
If you believe that your crawl space is growing mold that is impacting your family's health, contact our team here at Healthy Spaces at 812-602-4025 and our friendly staff will be happy to set up your free assessment.