Even in arid Arizona, native subterranean termite species must remain within relatively moist soil in order to thrive. The two most economically significant subterranean termite species in the state, desert subterranean termites and arid-land subterranean termites, see workers leave their central nesting site where they maintain foraging paths in moist soil. Foraging only in relatively moist areas of soil ensure that workers only encounter properly moist food sources, which include all types of dead plant matter that degrade slowly, such as dead tree roots, fibrous plant stems, logs, twigs, telephone poles, fence posts, and structural wood that makes contact with the ground surface.
Most subterranean termite infestations start after workers locate structural wood in contact with soil, but modern building codes prohibit structural wood from making contact with soil for this very reason. However, subterranean termites are able to access above ground structural wood in homes by using a hardening mixture of saliva, soil and bits of wood to construct air-tight shelter tubes that connect the ground soil directly to substructural wood components in homes. Amazingly, shelter tubes pass through narrow cracks and crevices in cement and masonry foundations where they are often found connected to sill plates, joists and other structurally important lumber components.
Subterranean termites are not able to infest dry structural wood; instead, workers must avoid dessication by nesting within, and consuming moist, and preferably, decayed structural wood. Therefore, moisture retention within soil that is located within crawl spaces, and adjacent to exterior foundations, must be kept to a minimum in order to keep a home well protected from the pests.
High moisture levels in soil are often caused by clogged gutters, plumbing leaks, and improper rainwater diversion. If the ground surface surrounding a home’s foundation slopes inwards, rainwater flows into crawl spaces, causing substructural wood to become saturated with water vapor. Naturally, the commonality of lawn irrigation systems on residential properties in Arizona may also contribute to moisture retention in the soil within and around crawl spaces. If a home’s gutters effectively divert water, and if rainwater and water from sprinklers drain away from a home’s foundation, then blocking rising water vapor by laying a 4 to 6 mil polyethylene sheeting over crawl space soil may be the last step to ensure that a home is well protected from subterranean termite attacks. That being said, the application of a perimeter termiticide barrier around a home, and annual termite inspections are highly recommended given the high rate of subterranean termite infestations in Arizona homes.
Is your crawl space soil covered to prevent water vapor saturation in substructural wood?