Did you know that there are building code specifications still in practice in some areas of the US that actually encourage mold growth? It’s unfortunate, but true. These codes have to do with the false idea that crawl space air can be ventilated to keep out moisture. This flawed idea of the ventilated crawl space has to do with the simple idea that vents let air circulate and dry up, which prevents moisture from collecting in your crawl space to cause mold. It makes sense, since air is known to dry things up. For this reason, these building codes specify the size, number, and position of crawl space vents.
But this outdated practice overlooks some key problems. While it’s true that ventilation exchanges air flow, the air in a crawl space circulates differently than we would expect it to and the relationship between the air vents and the air exchange rate within a crawl space are incorrect. With vented crawl spaces, hot summer days allow hot, humid air to cool in the crawl space. As the air is cooled, the humidity increases within the crawl space. Once the air exceeds 100% humidity it starts condensing on cool surfaces in your crawl space. These hazardous codes specifying crawl space vents were apparently made on incorrect assumptions or guesswork that was not discovered until recently. Now building designers recommend that crawl spaces be conditioned or encapsulated and unvented. This completely isolates the crawl space from the ground and the outside air with a vapor barrier and installs a dehumidifier. Crawl spaces can be the worst place to start mold growth. This is because mold, mold spores, and other volatile organic compounds will rise up through all levels of the house when the air is hot. This spreads mold to other surfaces and makes the air unhealthy to breathe. At least one third of the air breathed in a home is coming from the crawl space or basement. Of course, when considering the health of your crawl space, you have to take into account the climate of your home environment, the size of the space, the materials used, and a number of other factors that may be too complex for laymen. You must rely on a competent building designer to understand how your own crawl space will stay dry throughout the year.