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Wood Decay

The term "dry-rot" is often mistakenly applied to decay, suggesting that decay occurs in the absence of water. Most fungi can only decay wood which has free water within the cells which is when moisture exceeds 30% (by weight). Most wood in buildings range between 7-13%, and decay is not normally a problem in a well constructed, properly designed building with adequate ventilation and maintenance. The most common form of fungi decay in the Northwest, especially west of the Cascades is brown rot. Brown rot fungi is most common on softwoods, and at the advanced stages, their damage leaves the wood as a brown, crumbly mass with numerous cross-breaks perpendicular to the grain.

Signs of fungal attack in wood are often subtle. Decay is a gradual process which is divided into three stages: incipient, intermediate and advanced. No inspection device is capable of detecting incipient decay. However, clues to invasion may be detected as change in color, lack of luster or brashy appearance. Most decay can be detected at the intermediate and advanced stages by careful examination of the structure. Areas which are most subject to attack include: floors beneath kitchen and bathrooms, poorly vented crawl spaces, wood-soil contacts around perimeter of home, decks, wooden steps, railings and any areas where water is collected.

The simplest method for decay prevention and control is to eliminate any sources of moisture in the structure such as eliminating slow leaks, maintaining gutters, controlling ground water and keeping a vapor barrier over the soil in crawl spaces.
However, when Bugaboo gets the call to remedying a wood rot situation, we have some nifty solutions. 

First have the structural repairs done by a competent contractor. Then any remaining questionable wood can be treated with a borate solution.  One such product is is 

Identification

There are two main classes of wood rot. In one type, the decayed area has a brown discoloration and a crumbly appearance. It usually breaks up into variously-sized cubes, giving rise to the name "brown cubical rot." Another type of rot results in a white or yellow discoloration, with the decayed wood being "stringy" or "spongy."

Although many decay fungi may grow for long periods without producing any external evidence of their presence, others produce "fruiting bodies" on the surface of decaying wood. Fruiting bodies are usually "crusts" or shelflike "brackets" which are a few inches or so in diameter. The fruiting body of Serpula lacrimans, e.g., is a rust-brown, crust-like structure on the wood surface. It has a waxy appearance, with shallow, net-like folds or "wrinkles." The fruiting body of Poria incrassata is also crust-like. It is white to light buff when initially formed, but becomes brown as it ages and dries out. Small pores can be seen in the crust when it is examined with a hand lens. Gleophyllum trabeum forms bracket-like fruiting bodies. The upper surface of the fruiting body is dull gray-brown and smooth. The lower surface has elongate openings (pores) or split-like openings (gills). These fruiting bodies produce millions of tiny spores which may, in some cases, serve to spread the decay fungus to other areas.

Also, surface molds, "mildews," and stain fungi are often found growing on the surface of damp wood and can be confused with decay fungi. Although these organisms may discolor the wood, they do not break down wood fibers and thus do not weaken its structure. However, these organisms indicate that moisture is present and that decay will likely proceed if a wood-rotting fungus becomes established in the wood.

Life Cycle & Habits

Decay fungi are living organisms which send minute threads called "hyphae" through damp wood, taking their food from the wood as they grow. Gradually, the wood is decomposed and its strength is lost. Such damage is often inconspicuous until its final stages, and in a few instances homeowners have suddenly found floors breaking through or doors falling from their hinges due to wood rot.  When previously dry wood is placed in contact with moist soil, or in a location where it is subject to condensation (such as unventilated crawl space), it is likely that wood decay problems will occur. Rain leaks, faulty plumbing and leaky downspouts also are common sources of moisture. In some instances, water can be transported to the site of decay through strands or "rhizomorphs" of the decay fungi. Water-transporting strands may extend for thirty or more feet across brick, concrete or similar materials. The wood decay fungus, Serpula lacrimans, has been known to transport water up three stories to an area where decay is occurring. Poria incrassata is also capable of transporting water long distances. However, these fungi are exceptions to the rule. Most wood-rotting fungi must have a direct supply of water at the site of decay. Thus the term "dry-rot," sometimes applied to decay in wood structures, is erroneous.

Control Measures Prevention

1.If the decay hazard is high, select the heartwood of decay-resistant species or use wood   properly treated with a good preservative. Conifers from which decay-resistant lumber is produced include Pacific yew, juniper, redwood, baldcypress, and western red cedar. Durable hardwood species include osage orange, black locust, red mulberry, catalpa and black walnut.

2.Build on a well-drained site. Use proper grading to prevent water from seeping under the house. Install effective drain tile,  roof overhang, gutters, and downspouts. Place no untreated wood within 18 inches of the ground.

3.Provide adequate cross ventilation beneath buildings to eliminate dead air pockets. Install two square feet of opening for 25  linear feet of wall. Dense bushes or other plants should not be placed in front of these ventilators.

4.Install a vapor barrier on the soil surface to cause soil moisture to condense on the barrier and return to the soil rather than condensing on the floor and above joists. Satisfactory barriers can be made by covering the soil with asphalt roofing paper or polyethylene sheets.

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