The current thinking is that total eradication of termites from certain areas is unfeasible, and a more realistic approach involves containing existing insect populations and limiting risk to buildings. As with the moisture control strategies described above, the strategy for combating termites is based on the assumption that none of the following measures are 100 percent effective on their own, but, in combination, create conditions where the risk is negligible. The 6-S strategy includes the following lines of defense:⁸

• Suppression. This involves reducing termite populations in a particular area, and preventing their spread to new areas. An “area” can range from an entire state (though usually only if the termite is a recent introduction and still has limited distribution), to a single home. Methods of suppression include locating and destroying termite colonies, burning infested wood and heat-treating reclaimed lumber.

• Site management. Careful site preparation and clean-up helps to reduce the potential for termite infestation. If individual trees, forests or orchards have been cleared, it is essential to completely remove tree stumps and other buried wood from the site as well as construction debris that may contain cellulose. Water should be drained away from the site of the building. Wooden formwork for concrete should never be left in place.

• Soil barriers. Treating the soil is a popular and cost-effective option for protecting against conditions that lead to termite damage, especially in states like Louisiana and Florida where termites are a major issue. According to the North Carolina Department of Agriculture, the optimum time to protect against termites is during planning and construction, with the key objective of establishing a chemical barrier between the soil, where termites live, and the wood in the building.

Another option, which is sometimes used in California and Hawaii, is a physical barrier, such as precisely sized silica sand, crushed basalt, or granite beneath slab foundations and other locations. Optimum particle size ranges from 1/16-inch to 1/10-inch in diameter, as these particles are too heavy for the termites to move, and the spacing between them too small to move through. A more recent development is termite mesh to wrap the foundation, which protects at-grade or below-grade penetrations of foundations and slabs. Sufficiently fine mesh—1/32-inch—is recommended. Stainless steel mesh installed by licensed contractors will resist corrosion, though it can be costly.

Termiticide-impregnated membranes have also been used as a barrier, mostly in Japan, but don't have a long track record. They can be expected to have similar characteristics to termite shields in that they require very careful installation, and termites may be able to get around them. Termite bait systems can also be used as a substitute for the soil barrier, but require a long-term commitment to a contract with a professional company.

• Slab and foundation details. Slabs and foundation walls should be designed to inhibit the entry of termites into the building and to facilitate inspection for termite shelter tubes. If hollow concrete masonry units (CMUs) or double walls are used in foundations, they must be capped with concrete or masonry to eliminate holes. All exterior slab edges or foundation walls must be kept free of cladding for a height of 6 inches from the finished soil level to allow inspection for shelter tubes. This separation of cladding from the ground must allow for any landscaping to be done immediately after construction or likely in future.

An example of termite control for slab-on-ground construction. Images courtesy of American Wood Council

It's important to note that there should be no contact between the building woodwork and the soil or fill material. For best results, exterior woodwork should be at least 6 inches above ground and any wood in contact with or adjacent to the soil should be preservative treated.⁹ (For more details, see the section on code requirements on the next page.)