The support beam pictured is severely damaged by both wood decay fungi and subterranean termites.

Wood Destroying Organisms

Wood Destroying Organisms, or WDOs as they may be referred to by pest professionals, include a variety of insects and wood decay fungi.  Wood destroying insects may include certain types of ants, bees, beetles, termites and wasps. These insects include but may not be limited to carpenter ants, carpenter bees, various beetles and termites. Of these insect pests, termites are the most destructive structural pests

Conditions Conducive
Left unchecked, or not corrected, conditions conducive to WDOs can result in extensive structural damage. Nearly all WDOs require certain conditions which are conducive to their survival and growth. Of these, the most important is the presence of elevated levels of moisture. As such, the elimination and control of moisture sources can serve to prevent arrest or control certain WDOs and the associated resulting damage. This is so because these WDOs require the presence of certain levels of moisture to survive and thrive.

WDO Type Moisture Threshold
Decay Fungi ~ 25% and above as per Massachusetts Institute of Technology
Boring Beetles ~ 8% and above as per University of California, Davis
Subterranean Termites Termites are capable of importing moisture themselves so moisture content is not a limiting factor for subterranean termites. Sources of moisture include plumbing leaks, roof leaks, faulty construction, clogged gutters and leaders, faulty grade levels, soil borne moisture and others.  Suitable correction of these moisture sources is necessary to eliminate these moisture sources. Experienced and competent pest professionals who conduct WDO type inspections will provide information and recommendations to their customers regarding conditions conducive and moisture sources observed during annual inspections.

Inadequate crawl space ventilation is a contributing factor to excessive moisture levels in soil crawl spaces as well. This is so because soil borne moisture may elevate the moisture levels present within a crawl space such that certain insect pests and wood decay fungi may thrive resulting in damage to structural lumber.  The national building code recommends one square foot of crawl space vent for each one hundred and fifty feet of soil crawl space present. This recommendation is reduced to one square foot of crawl space vent for each 1,500 square foot of soil crawl space when a moisture barrier, such as poly sheeting, is in place. Note that this is a significant tenfold reduction in ventilation. In my observation and experience, this tenfold reduction does not provide adequate ventilation to properly address and prevent elevated moisture levels in all crawl spaces.  As such, the presence and threat of crawl space moisture should be included in all annual inspections for WDO purposes.