Termite Resistance - One Line of Defense Isnt Enough

Claudette Reichel  |  6/24/2008 1:09:53 AM

Figure 1, Stainless steel mesh collar around pipes to be embedded in slab prevent hidden paths for termites

Use multiple methods to make your home resistant to damage from termites, especially Formosan subterranean termites, and other wood-destroying insects. Formosan termites can cause major structural damage within a year of infestation, so if they have been found in your area, include additional protection. Since basic controls and most state- approved, stand-alone treatments are not fool-proof, it’s wise to invest in a second line of defense or even a termite-resistant total structure (no untreated wood, foam or paper in the structural shell of the house, or even throughout the entire house).

Basic controls: Make sure that no untreated wood, such as concrete forms, is left in the soil after the foundation is completed. Do not use standard foam insulation in or near ground contact; termites and carpenter ants can tunnel through it undetected. Termites are attracted to and sustained by wet materials, so moisture-managed construction techniques are essential to prevent both decay and termite damage. (See Moisture Control section.)

In addition, make sure that your home is designed and constructed to allow for termite inspections and to prevent or shield hidden pathways (including porches, decks and their supports, garage, etc.). Leave an 8-in. clearance between cladding and finished grade so that future termite tunnels are visible, even if mulch is added to the soil. Keep plantings a minimum of 3 feet from the foundation. Use metal flashing caps or termite shields between raised foundations and framing to force termites to reveal themselves or their tunnels.

Soil Treatment: In chemical soil treatments, the soil beneath and around a building should be professionally treated with a labeled termiticide before adding slabs and piers, and a perimeter treatment should be performed after final grade. The soil is treated with a liquid termiticide under and around a structure to create a continuous chemical barrier that blocks potential routes of termite entry. If the chemical barrier is broken, such as from soil disturbance during construction or walking on it, termites could enter through those gaps. The chemicals approved for use may last from 5–15 years. Choose the longest lasting treatment available, but keep in mind that flooding or a high water table can affect it.

Steel mesh barrier system: A common hidden entry point for termites is through plumbing penetrations in a slab and mortar or other joints in foundations. Termites can go through 0.03-inch cracks. Conventional sealants and membranes are not reliable barriers since Formosan subterranean termites are known to chew through many noncellulosic materials they do not eat, including foam insulation, mortar, plastic, rubber and others.

A flexible stainless steel mesh can be cut, shaped and bonded on site by trained installers to provide effective and permanent termite barriers around plumbing holes, in expansion joints, over stemwall and pier foundation perimeters and other areas. When installed on a raised foundation, the mesh should extend through the cladding to force termites behind the foundation finish to reveal them.  (Figure 1, Steel Termimesh Barrier Around Pipes)

Borates are highly toxic to insects and decay fungi, but have low toxicity to people and the environment. Termites normally begin to feed on borate-treated wood products, then die off and not form tunnels on the treated wood to reach untreated wood or paper, an advantage over other termite resistant materials. Borate pressure-treated lumber and wood products manufactured with borates (plywood, engineered woods, cellulose insulation) can be used in framing, but should not be used outdoors or in ground contact. The borates can leach out if in flowing water or the ground. Normal fasteners can be used in borate treated woods.

A registered borate barrier system can be spray-applied to all structural wood in a 2-ft. uninterrupted band from the sill upward and on all wood floor framing. This treatment system is designed to prevent termite tunneling on the wood as a barrier to prevent access and damage to untreated wood beyond the band. This borate solution can penetrate wood over time, but may not always penetrate to the core for total protection.

EPS rigid foam (beadboard) made with borates is available and offers protection from hidden termite tunneling. But, until more performance experience is available, the recommendation to have no foam insulation in ground contact is prudent, even treated ones, especially in areas with high risk from Formosan subterranean termites.

Copper-based and other pressure treatments of wood (such as ACQ and Copper Azole) are stable so the wood can be used outdoors and in ground contact. It should be used for wood decks, porches, fencing and other outdoor uses. It is highly resistant to wood-destroying insects and decay. Termites will not feed on the treated wood but will tunnel over it to reach untreated wood. CCA treated wood has been phased out for general use due to concerns about the arsenic it contains.

Termite resistant materials contain no food for termites – including treated wood products, concrete, steel, many composites and plastics, fiber cement, brick and stone, borate containing foam and cellulose insulations, ceramics, glass and paperless drywall. Even concrete, steel and pressure-treated wood building systems can become infested with termites that find their way to moisture and untreated wood or paper such as untreated wood roof framing over concrete walls, paper in drywall and interior woodwork. Hidden pathways must still be prevented.

Landscape controls are important to protect both your house and trees. Formosan and other types of termites eat the core of live trees, which weaken them and have resulted in much tree damage to homes in storms. Choose termite-resistant mulches near your house and trees. Investigate and plant trees near your house that are less likely to become termite infested.

For more information on integrated pest management for protecting homes from termites, visit www.LouisianaHouse.org or your local LSU AgCenter extension agent.

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