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Homeowners with excess moisture in their crawl spaces often wage war with wood-destroying organisms, such as wood-decaying fungi, termites and wood-boring beetles. But winning the war means first solving the moisture problem, not battling the bugs and fungi.
The first step is to ask, “What is the problem?” and then once it’s identified, “What is the best way to correct it?” Chemical treatment to prevent an invasion of wood-destroying organisms is not a means of correcting the moisture problem. Before calling in pest control operators, homeowners should find the moisture trouble spots in their crawl spaces and take steps to alleviate the wetness.
A moisture barrier of 4 or 6 mm. of plastic sheeting covering a minimum of 70 percent of the crawl space will often reduce moisture levels. The plastic should cover the dampest areas of the crawl space, and the homeowner should make sure that water does not collect on top of the plastic.
Improving crawl space ventilation may also help. Homes should have one square foot of ventilation per 150 square feet of crawl space area without a moisture barrier, or one square foot of ventilation per 300 square feet with one (moisture barrier). Ventilators should be kept open as long as the weather is warm, and obstacles, such as shrubs, that might impede air circulation, should be pruned or removed.
To insure proper drainage, the contours of the land around the home should slope down and away from the house on all sides. Obviously, you need to make the slope gradual enough so that water doesn’t puddle inches from the foundation. If altering the contour is not feasible, the homeowner should consider installing some sort of exterior drainage system. There should be a 24-inch clearance between the soil and any wood, although 18-inch clearances are fairly common. Pressure-treated lumber is recommended for areas with less than 18 inches of clearance or with direct wood/soil contact.
Using borates may be advisable if moisture levels cannot be reduced or if evidence of active wood rot and insect infestations exists. Unlike some other pesticides, borates, chemicals derived from borax, are effective against fungi as well as insects. Borates should be applied by licensed pest control operators to bare wood surfaces by spraying, painting or injection.
It can take several weeks or months for borates to fully penetrate into the wood. The higher the moisture level of the wood, the quicker the penetration occurs. Before deciding on chemical treatments, homeowners should request that pest control operators identify moisture problem areas and collect wood/moisture readings. Mold, mildew or sap-staining fungi are indications that moisture has been a problem at some point, but not necessarily at present. These particular fungi do not affect the structural integrity of the wood, and unless the moisture level is near saturation, over 25-percent, the more serious wood-rotting fungi will not develop. The same is true for wood-destroying insects. They also prefer wood with high protein and moisture levels.
The bottom line is that unless a real problem is identified, then homeowners should not sign up for treatments that they may not need nor will accomplish what some sales representative’s claim.