Too much moisture in a home can lead to mold, mildew, and other biological growth. The presence of these molds can lead to a variety of health problems including allergies (my problem) asthma and more serious respiratory problems. In addition to health problems, excess moisture can lead to problems such as rot, structural damage, and paint failure and create a hospitable environment for pests. For example, termites require moisture in order to survive. Although ridding an infested house of termites requires an integrated pest management approach that includes a conventional chemical treatment or the use of baits, there are steps a homeowner should take to make a house less ideal for termite invasions to minimize the use of chemicals. Subterranean termites and drywood termites are the two general types. Subterranean termites "nest" in the soil and from there they can attack structures by building shelter tubes from the soil to the wood in structures. Subterranean termites cause more of the damage to homes and structures than drywood termites so will be my primary focus here. Termites will attack any material with cellulose, including wood, paper coated wall board, and paper (as in that treasured book collection). Wood that is at least 30 percent water saturated provides enough moisture. Additionally, termites will find free-standing water such as condensation, rain or plumbing leaks and use this moisture as their main source for survival.
Correcting and preventing moisture problems is a first defense against termites and should be considered before prophylactic application of barrier termiticide post construction. It is to be noted that many states (especially in the south east) require the application of termiticide chemical barrier before construction as part of site preparation. These preconstruction treatments are required to be effective for five years. It is reported that the newer, biodegradable chemicals are effective for 5-11 years; however, some termiticides breakdown easily in water and should not be applied within 50 feet of a water well or the water table. Other chemicals are more persistent and cling to soil. There are other techniques that should be used first and should be used as part of a termite management strategy. According to BIRC (The Bio-Integral Resource Center in Berkeley, CA) prevention and early detection are the most effective methods of reducing the use of toxic chemical in termite control. As a side note BIRC has an “ask the expert” section of their organization web site where they will help you identify the least toxic solution to your pest problem. They are really nice so ask away.
Rain water should not run up against the house (nor should plant irrigation water). The soil level against the exterior walls should slope away from the building. Even in areas where the natural topography is towards the house and artificial slope should be created in a shallow “V” to prevent water from pooling around the foundation. The ground around the home's foundation should be graded to slope down and away from the house at a rate of 1/2" to 1" per linear foot to drain surface water away from the house. If need be a French drain should be dug an adequate distance from the house. Most houses are built with the soil level sloped away from the building, but landscaping and time can undermine this. Plants should not be planted closely against a structure to avoid “watering the building” instead of the plants.
Water from down spouts should be directed away from the house, discharging at least a few feet from the foundation. If the natural flow of water is to pool in any location, it may be advisable to direct all down spouts to a dry well system or pipe to a more natural drainage location. Test any underground drains with a hose to make sure they are working properly. Often underground drains become blocked with debris or broken and allow water to drain against the building. Drains that are not working should be repaired or replaced. Be sure that driveways, sidewalks, and patios slope down and away from foundation walls at 1/4" per linear foot.
If these solutions do not eliminate a moisture problem then the next steps will have to be taken. In extreme cases, you may have to dig out around the foundation and replace the fill with an exterior drain tile and with a good draining material such clean gravel. Because this can be very expensive in existing homes, all the previous solutions should be rigorously tried first. In some areas, there may not be enough room outside the dwelling to provide proper drainage - in these cases; it is often recommended that interior drain tile and a sump pump be installed to remove water from basements and crawlspaces. This is very expensive and messy, but is extremely effective.