CONTROLLING CRAWL SPACE MOISTURE: HOW AND WHY IT SHOULD BE DONE

A homeowner's guide to controlling moisture, mold, and the destruction of structural framing in crawl spaces.

Many homes in Indiana and Michigan have crawl spaces. Most homeowners are either unaware of moisture problems in the crawl area until it causes structural problems, or are at a loss as to how to handle the problem once they notice it. The following is an informative guideline to solving crawl space moisture and related problems.

Contrary to popular belief and older building code recommendations, venting of the crawl space is detrimental to solving a moisture problem. In one case, according to the National Association of Home Builders, a home in La Plata, MD had a crawl area moisture problem that was only made worse by adding vents and ventilation fans. Only after closing off the vents and adding a dehumidifier was the problem improved (see Nation's Building News Volume 18, Number 3). Warm, moist air (very common to this area in the warmer months) entering the crawl area through a vent will condense into water droplets on cool surfaces such as the floor, water pipes, framing members, exposed nail or screw heads, items stored in the crawl, or any other surfaces that may exist. This is the same process that causes water to condense on the interior of glass windows during the colder months. According to chief executive officer of the Institute for Environmental Assessment, when it comes to mold growth "As (contractors), you can't control the other factors (food, temperature), but you can control moisture". "Keeping this in mind, the first step is to create controlled environment" in the crawl area and the first step is sealing off any vents or other openings. In their handbook "Mold Remediation in Schools and Commercial Buildings" (publication EPA 402-k-01-001) the Environmental Protection Agency says "The key to mold control is moisture control" and "ventilate only if the outside air is cold and dry, dehumidify if the outside air is warm and moist" and finally "Don't let foundations stay wet. Provide drainage and slope the ground away from the foundation". As an added benefit, sealing the vents will decrease the likelihood of frozen pipes, and saves on energy costs as less cold air is allowed into the crawl area.

Once air moisture condensation is controlled, a drainage system of some type will usually need to be installed. Nearly every crawl space will experience ground-moisture problems at some point. While it is not always evident in drier times, water will enter the crawl area during wetter times. This may happen on an annual basis, or every few years. Regardless of how often the problem occurs, the damage caused by rotting of wood framing and mold should not be ignored. Drainage systems may be constructed of drain tile for dirt floors, or with newer products designed for concrete floor applications. With either type of system, the installation of at least one sump pit with a pump and proper discharge will be required. More than one would be needed for larger crawl areas, or where crawl areas are divided into sections.

As mentioned above, once a moisture problem is finally noticed there is usually structural damage that will need to be repaired. The most common form of structural damage is to the floor joists, sill plates, and band joists. All of these items are critical to the structural integrity of the home and should be repaired by a contractor experienced in crawl space structural repair and renovation. This is also the time to address installation of supporting posts and/or beams, along with any foundation wall crack repairs. These repairs can be expensive, as framing work in a confined area such as a crawl space is much more difficult than working in a more open area. This is also the time to remove all debris and any unused wiring and/or piping for a safer and cleaner working environment.

If there is no gutter and downspout system or if the existing one is in need of repair, this should be taken care of. Once an adequate system is in place, it should have some type of downspout extension to carry the water a minimum of 10' away from the foundation walls, instead of emptying next to the walls. While this can be achieved in a variety of ways, an underground extension system leading to a grate box with a drywell is the best option. Another exterior concern is the grading of the landscaping. Soil and landscaping around the foundation should slope a minimum of ½" per foot for the first ten feet from the foundation wall out. If a proper grade cannot be achieved, then the installation of an exterior curtain drain or a dewatering ditch may be necessary. While the exterior solutions are necessary to help lessen a moisture problem, they will rarely solve it completely. At this point, you have sealed off the crawl area, installed a drainage system, and corrected any exterior problems that may be contributing to the moisture problem. There are still a couple of things you should do to completely solve the problem and improve the energy efficiency and comfort of your home.

The next step is to install a vapor barrier of some type. In a crawl with a dirt floor, a specially designed, tear-resistant vapor barrier should be installed. Properly installed, it should overlap at the seams and the entire perimeter should run up the foundation wall a minimum of one foot and be sealed there with an adhesive urethane. This same process can be used in crawls with a concrete cap or floor, although installing ½" or thicker foam panels will do the trick and provide insulating properties, not to mention a much more comfortable surface to crawl on when working or storing things in the crawl. The foam panels should be butted tightly together. These barriers are necessary to stop the transmission of moisture vapor up from the ground and into the crawl environment. Although the ground or floor may look dry, negative pressure (caused by heating and cooling systems, ventilation, or fans in the main levels of the home) will draw moisture vapor up through the soil or floor, where it will eventually settle on the surfaces within the crawl area, potentially defeating all the efforts put forth up to this point.

Insulating the interior foundation walls with rigid foam panels butted tightly together will act as a moisture barrier against exterior ground moisture entering via a capillary (water "wicking" from the outside in) action that can occur in all forms of foundation wall construction, but especially prevalent in cinder block walls. In addition to forming a moisture barrier, this will provide insulating properties as well, lowering your overall energy cost in both the summer and winter. Box sill (the area between the top of the foundation wall and the bottom of the main floor) insulation is important as well, and is best achieved using batten fiberglass insulation with a minimum 4" thickness. Please Note- if there is insulation in between the floor joists, it should be removed. It is no longer necessary, as the entire perimeter has been insulated from the exterior temperature extremes, and is a collection site for both condensation and insects. The final step to turning your crawl space into a "Controlled Space" is to add a dehumidifier. A 40-pint unit will usually do the trick, but be sure to check the manufacturer's recommendations for your situation. The dehumidifier should drain directly to the sump pit, allowing it to run as often as it needs to without the hassle of emptying a bucket every few hours. Be sure to follow the manufacturer's recommended settings.

Once the above recommendations have been put in place, you will have a controlled environment in your crawl area. The comfort level and value of your home has been dramatically increased, you have eliminated one of the leading causes of mold problems, and stopped the potential for framing damage leading to costly repairs. If done properly, you will also pick up some valuable storage space.

In the past, homeowners thought that a wet or damp crawl space was something they just "had to live with" not knowing the damage that could be done to the structure or the impact mold can have on personal health. As you can see, it does not have to be that way. This type of work is expensive investment, but comes with many short and long term returns. Considering resale value, personal health, energy savings, and preventing structural damage, this work may be one of the best investments you can make in your home. In addition, many states are now revising their building codes concerning crawl spaces to match the above recommendations (see Indiana Builders Association "Informational Report on Mold" January 2002).

James Nova, President of Nova Foundation Repair, Inc. in La Porte, Indiana wrote this informational article.