What's a little water under the house going to hurt, you ask? Excess moisture can lead to a glut of problems, such as repulsive odors, rotted framing, structural pests, foundation movement, efflorescence, and allergy-irritating mold.
A musty or pungent odor usually accompanies efflorescence and excessive moisture. Accordingly, a good nose proves invaluable in investigating the problem.
Here are some common causes of moisture:
Leaks in water and sewer lines: A failing plumbing fitting or corroded pipe is often the culprit. Fit a replacement or install a repair "sleeve" around the damaged section of pipe.
Leaks in sinks, tubs, and toilets: A wet basement may be the result of a leaking toilet, tub, or valve located in the walls above.
Overwatering planters surrounding the house: Adjust watering time, water less often, install an automatic timer, or adjust sprinkler heads to solve this problem. Convert the traditional sprinkler system to a drip irrigation system.
If your moisture problems aren't related to plumbing and watering, you may have some type of drainage issue. You can reduce problems with several common techniques:
Install rain gutters: Without gutters, rainwater collects at the foundation and eventually ends up in the crawlspace or basement. If you already have gutters, keep them clean and make sure that your gutters and downspouts direct water a safe distance away from your house.
Drain water away from the house: The earth within 30 inches of the foundation should slope down and away at a rate of 1/10 inch per foot.
Improve ventilation: Passive ventilation is natural ventilation that doesn't use mechanical equipment. Foundation vents (metal screens or louvers) and daylight windows for basements are the best sources of passive ventilation. Active ventilation involves mechanical equipment, such as an exhaust fan.
Passive ventilation allows nature to be your workhorse. You save on your utility bill and help the environment by not relying on fossil fuel. But don't hesitate to use active ventilation if your crawlspace or basement needs it.
If you use passive ventilation, you must keep vents clean to allow maximum airflow. Thinning shrubbery, vines, and ground cover may be necessary from time to time.
Install a vapor barrier: Excessive dampness in a crawlspace or basement can condense, causing floor framing to become damp, covered with fungus, efflorescence, and rot. To prevent this damage to the floor framing, install a vapor barrier consisting of one or more layers of sheet plastic (six mil visqueen) on top of the soil in the crawlspace or basement.
The plastic should be lapped a minimum of 6 inches and sealed with duct tape at the seams. Cut around piers and along the inside edge of the foundation. In severe cases, the plastic can run up the sides of piers and the foundation and be secured with duct tape or anchored with a line of soil at the perimeter.
Try a French Drain: If the previous suggestions don't help, it's time to call in a soils engineer to determine whether the condition requires the installation of a French Drain, which is an elaborate drainage system.