QDEAR BARRY: My vacation home sits vacant for several months at a time. When I return, the water always has a strong sulfur smell, like rotten eggs. What could be causing this problem? Is it unsafe? How can I keep it from happening? -- Patrice

ADEAR PATRICE: Water heaters contain a specialized metal rod known as a sacrificial anode. Its purpose is to absorb the corrosive effects of minerals in the water and thereby prevent deterioration of the water tank. Gradual deterioration of this rod produces small quantities of sulfur and hydrogen gases. When the water heater is used daily, these gases pass from the plumbing system without being noticed. When the house is vacant and no water is drawn from the tank, the sulfur and hydrogen accumulate. The sulfur dissolves in the water, causing the rotten egg smell you notice. The way to eliminate this smell is to drain the tank to the yard, by way of a hose.

The sulfur itself isn't harmful; hydrogen, however, is highly combustible. Hydrogen accumulates at the top of the water heater tank. When it is released through open faucets, it can ignite or explode if exposed to a flame or spark. For example, if the dishwasher is the first fixture you operate after you have been away from the property for a long time, the fixture can become filled with hydrogen. A spark from the electronic controls can cause the appliance to blow up. For this reason, draining your water heater to the exterior is doubly recommended.

To prevent the formation of gases in your water heater, you can winterize the plumbing system. This involves opening all faucets, turning off the main water supply valve to the building and draining the water heater.

DEAR BARRY: There's a lot of moisture and humidity in the crawl space under my house. The insulation is so saturated with condensation that it is falling down in places. Mold appears to be growing on the wood framing. What can I do to correct this? -- Ken

DEAR KEN: Condensation in the sub-area beneath a house usually indicates insufficient ventilation. The building code requires that crawl spaces be cross-ventilated and that the combined area of total vent openings be at least one square foot for each 150 square feet of floor area. This is a minimum requirement; it's not sufficient in all cases. When vents are not provided or when they are blocked by insulation, or if the vapor membrane on the insulation is on the downward side, rather than against the subfloor, moisture can condense. That can cause mold, as you have noticed, or fungus, resulting in dry rot to the floor structure.

You should try to eliminate the moisture problem, and also to evaluate and correct any problems the moisture has caused, such as mold, fungus or dry rot damage.

First, remove all the floor insulation. That way, a licensed pest control operator can make a thorough evaluation of the wood framing and subfloor sheathing. Mold testing would also be advisable to ensure against any health risks associated with mold.

And finally, be sure that the sub-area is thoroughly ventilated, at least in accordance with minimum building code standards.

Barry Stone is a professional home inspector. If you have questions or comments, contact him through his Web site, www.housedetective.com, or send mail to 1776 Jami Lee Court, Suite 218, San Luis Obispo, Calif. 93401.

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