Owner discovers moisture problem under house

Q. While doing some wiring under my house, I found a moisture problem that looks serious. The ground is muddy, and there are small puddles in various places. What concerns me most are water droplets hanging from the floor framing and mold that seems to be growing on everything. I asked my next door neighbor for permission to look under his house. His soil was also wet, but there was no moisture or mold on the framing or other building components. Why am I having this problem?

A. Ground moisture under houses is common in some neighborhoods. It is often caused by the drainage characteristics of the property or locale. The effects are obviously worse during wet weather or when landscaping is overwatered. In most many cases, as with your neighbor's home, this is not a serious problem. However, if the crawl space under a building is not adequately vented, increased humidity can cause moisture condensation on building components, leading to problems involving fungus and/or mold. In all likelihood, your neighbor's subarea is adequately vented, while yours is probably not.

The building code requires cross-ventilation of crawl spaces below buildings, with vent openings equal to at least one square foot for each 150 square feet of floor area. If your home does not comply, additional ventilation should be provided by installing more vent openings or by adding a mechanical ventilation system. When adequate venting is not possible, the alternative requirement is to cover the ground with a plastic membrane to reduce humidity. Evaluation by a licensed general contractor or a qualified home inspector is advised to determine the most practical approach.

Since you may also have mold in your subarea, evaluation by a certified environmental assessor is advised. It is also likely that there is fungus infection of wood members. Therefore, evaluation by a licensed pest control operator (commonly known as a termite inspector) is also advised.

Q. Our dishwasher has an airgap device in the drain line, but it is installed under the sink because there is no hole for installing it in the rim of the sink. The people who are buying our home hired a home inspector, and he says the airgap must be located above the sink. As long as it is working, what difference does it make if it's installed above or below the sink?

A. Most people have seen an airgap on the rim of a kitchen sink, without knowing what it is or why it is there. An airgap is the 2½-inch round object that gurgles when the dishwasher is draining. It is there to comply with a heath safety requirement: to prevent a potential sewage backup in the sink from draining into the dishwasher. But why, you ask, does it matter if the airgap is installed under the sink? Here's the reason:

A dishwasher drain hose can become clogged with food particles. When this happens, water is unable to flow through the airgap to the sink drain. Instead, water is expelled through the opening in the side of the airgap. When the airgap is installed in the sink rim, the water can flow directly into the sink. If the airgap is located beneath the counter, overflow can cause flooding of the cabinet and the kitchen floor.

To avoid water damage, have a plumber bore a hole in the rim of your sink to enable proper installation of the airgap.

• To write to Barry Stone, visit him on the web at www.housedetective.com, or write AMG, 1776 Jami Lee Court, Suite 218, San Luis Obispo, CA 94301.

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