Wood Rot and Wood Decay Fungi

Wood rot and wood decay fungi damage is often characterized as moisture damage. However, while excessive moisture may cause some damage to wood, what causes more significant damage to wood is wood decay fungi which feeds upon, consumes and destroys the wood.

Wood decay fungal spores may be omnipresent and can germinate when moisture levels reach the level necessary for fungal growth. While moisture levels above 28% are sited in various references, some references, such as the Ohio State University Extension Fact Sheet and the Wood Protection Guidelines published by the National Institute of Building Sciences, state that wood decay fungi may grow when moisture levels reach just 20% or above.

There is no question that the presence of elevated moisture levels within structures present conditions conducive to both wood destroying insects as well as wood decay fungi. As such, the primary practice to prevent damaged from wood decay fungi is to prevent and reduce moisture.

Moisture can become a problem within a structure from various sources. Soil borne moisture is usually a problem in crawl spaces because moisture which emanates from the soil can impinge and condense on the structural support framing lumber of the sub floor where wood decay fungi can then thrive. Soil borne moisture in crawl spaces is usually controlled by the installation of a vapor barrier and sufficient crawl space ventilation. In some situations it may be necessary to install power vents and/or specialized crawl space dehumidifier systems manufactured and installed for such purposes.

Moisture is often cited as a primary cause for termite damage however, this may not be so because while some of the wood where elevated moisture is present may have termite activity, nearly all such wood will be damaged by wood decay fungi when such wood is allowed to be subject to elevated moisture on a continued basis.

Other sources of moisture of concern include plumbing leaks, surface water due to incorrectly graded soil, roof leaks and other such sources. Since moisture has long been known as a condition conducive to wood destroying fungi, termites and other wood destroying pests, structural inspections conducted by pest and other professionals should include the detection and identification of moisture sources. Recommendations should be provided to address the correction of conducive conditions identified during such inspections.

Wood decay fungi damage can be differentiated from that of subterranean termites by the absence of mud and excavated galleries which are characteristic of termite activity. Additionally, while termites feed and damage wood with the grain, wood decay fungi damage can be across the grain. Wood decay fungi damage may vary dependent upon the type of fungi which damaged the wood.

Brown rot type fungi may stain the wood brown and the damaged wood will form cube like sections. Fungal damaged wood may take on a yellow or whitish coloration accompanied by a reduction in weight and density. Wood damaged by such fungi may also appear soft, spongy and/or string like when probed and inspected.

Conditions conducive to wood decay fungi, and other wood destroying organisms, are observed and detected during a thorough inspection conducted by an experienced and competent professional. Such inspections should be conducted on at least an annual basis to assure that conditions and telltale signs of WDO activity are observed prior to the occurrence of significant damage to the structure.