Just as every attic requires proper ventilation and circulation for heat exchange and humidity control, the same is true for the crawl space beneath your home if it’s raised. This can be particularly challenging for raised homes that sit lower to the ground or closed crawl homes with a solid foundation wall around the entire structure that is open in the middle, or separated by a labyrinth of chain walls and compartments. The general rule of thumb in the attic is that there should be a minimum of one square foot of ventilation for every three hundred square feet of attic space, which can be achieved by gable vents or ventilated soffit panels staggered every few feet around the eaves of the home. This same rule of thumb should also be followed in the crawl space, whether the crawl space is open on all sides or by making sure vent openings are present in the foundation wall if not. In fact, the need for proper ventilation and circulation is even more important in the crawl space, since you are dealing with a number of humidity and moisture factors that typically don’t exist in the attic. It becomes less a matter of energy efficiency and more a matter of preserving the structural integrity of your subfloor and protecting it from long-term moisture damage that can sometimes necessitate extensive repairs or entire rebuilds.
A common problem in low or closed crawl space homes is the rising damp from the ground beneath. The humidity constantly rising from the ground beneath your home turns into a gas during the hottest parts of the day, and without the right amount of open air and circulation, this vapor can attack the framing of your home in the form of mold and wood rot, weakening your subfloor and potentially causing damage on a massive scale. Moisture and condensation from plumbing pipes under the home, old leaks that were never allowed to fully dry in the humid environment of the crawl, outside flooding events and differences in the dewpoints of building materials are all factors that require proper ventilation and circulation to keep the threat of moisture damage at bay.
Depending on the layout of your home, there are a few different steps you can take to make sure your crawl space can breathe and dry itself out properly when needed. First, if your home has an open crawl space in which you can see underneath from all sides, make sure that the landscaping around your home is such that excess water is allowed to drain out from underneath rather than being trapped inside due to changes in elevation that sometimes occur during the building process. The land should never slope towards a home of any construction type, so if the soil outside your exterior walls is higher than the soil underneath, make fixing that the first priority in your moisture control mission. While inspecting your crawl space, look for leaks, listen for drops from plumbing pipes, and be on the lookout for any areas of standing water which could also be wreaking havoc on your subfloors.
In the case of closed crawl space construction, you should have open and unobstructed vents about every five to ten feet around the house, and you may event want to lay down a moisture barrier on the soil underneath to help block some of the rising damp coming up from the ground. However, these barriers have a limited life span, and it’s still vitally important to control the humidity above them. Even if you have the right amount and positioning of vents, you may still need to install a timed blower or exhaust fan near some of the vents to achieve the right amount of circulation, especially in the case of multiple closed chain walls within the vented exterior. If you notice moisture damage already present on your subfloor and framing, contact your local licensed mold remediation professional. They can treat your subfloor with a borate product that will make the wood more resistant to moisture in the future, and give you even more tips about protecting your home from moisture damage.