Facts About Wood Damage Cause by Rot

Identifying causes of dry rot and tips for wood restoration and repair

by www.Aerotechlabs.com

Wood rot is evident in many home construction materials, the repairs for which constitute 10 percent of wood production sales. While many blame termites for such damage, no evidence supports this. Termites leave visible signs of their presence, deteriorating wood as they tunnel within and eat it. Sawdust particles are telltale signs of their encampment. Wood rot, on the contrary, is caused by undue exposure of untreated wood to moisture. Consequently, prevention constitutes both avoiding such exposure and employing a prevention and treatment program where rot already exists. Wood with 20 percent moisture content and green lumber remain at risk.

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Two types of rot trouble homeowners. The first is white and yellow with a stringy and spongy look. The other is brown and crumbly in appearance, and a tendency to break into cubes has earned it the nickname "brown cubical rot." These visible manifestations of wood rot are called "fruiting bodies." About 3 inches in diameter, these crusts or brackets are evidence that the particular decay fungi is present within the wood. Serpula lacrimans, Poria incrassata and Gleophyllum trabeum each have singular fruiting-body appearances. Fruiting bodies produce spores, which spread the decay fungus throughout the wood.

Decay fungi are living organisms that send hyphae through damp wood, taking food from the wood to grow, and thereby decomposing it. Even dry wood may become infected when placed near moisture. Water is transferred to decay by way of strands (rhizomorphs) of decay fungi. These strands are sometimes up to 30 feet in length. Serpula lacrimans has been known to transport water up three stories to the site of decay; however, most fungi need direct water at the decay site. Consequently, "dry rot" is a misleading and erroneous term.

To prevent wood rot, use treated wood or the heartwood of a decay-resistant species. Pacific yew, juniper, redwood, bald cypress, western red cedar or hardwoods like osage orange, black locust, red mulberry, catalpa or black walnut are all good choices. Build on a well-drained site and allow for cross-ventilation under buildings. Often, poorly vented crawlspaces develop wood rot as moisture from the soil penetrates the floor joists. Additionally, a vapor barrier on the soil assures that any moisture escaping the soil will be reabsorbed by the soil rather than the wood. Asphalt roofing paper or polyethylene sheets provide adequate protection.

To repair damaged wood, first find and remove the source of moisture. Wood will dry and decay will stop. Remodel and improve ventilation and drainage issues before replacing wood. Then cut one foot beyond the rotten wood, never placing new lumber on decay. Treat replacement lumber with chemical products. In lieu of replacing wood, remedially treat wood by permeating affected areas with chemical solutions. Diligent treatment of affected wood will protect the structural integrity of the home and prevent further damage. For more info, see http://ohioline.osu.edu/hyg-fact/3000/3300.html

Reprinted with permission from an abstract from Ohio State University Extension Fact Sheet, that was printed in the Aug/Sept. 2003 issue of the American Indoor Air Quality Council Newsletter.

First Published: Late-October, 2003
Updated: February 2007

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