We have recently been battling the dreaded Coptotermes formosanus, or Formosan subterranean termite, here in the coastal South. Longer periods of insect activity correlate with higher temperatures and extended seasons driven by climate change. In addition, the termites’ range is extending north as temperatures increase, placing new geographic regions at risk of infestations.
Our own office, a wood-frame structure aged six years had a tiny penetration which allowed water into the wall, creating highly desirable conditions for termites, who entered through the (treated) sill plate at the perimeter wall and converted the open-cell spray-foam insulation into a termite gallery. We only realized the extent of the problem when they began chewing through the interior gyp board; we stripped away the interior wall finish to find the damage extended from slab to header, and about 10 feet in width. The robust colony was swarming in November, an unseasonal time of year.
Treated wood is resistant to termites and decay, but it isn’t traditionally used within walls at the interior side of weatherproof enclosures. The South has a lot of Southern yellow pine, which has a high concentration of the cellulose that termites love to eat, but the code requires only the sill plate and exposed framing to be pressure-treated with ACQ (alkaline copper quaternary – made up of copper, a bactericide and fungicide which makes wood resistant to biological attack, and a quaternary ammonium compound which acts as a biocide which increases the tolerance of the timber to copper-resistant bacteria and fungi, but also acts as an insecticide.)
Treated lumber is about 20% more expensive than untreated lumber, but its pest-resistance may become the preferred method for dealing with termites. Alternatives include using materials with even less vulnerability to insects, such as light-gauge metal framing, masonry, or concrete, which may have greater cost, but also offer long-term durability.
Siding historically provided the most vulnerable material for termites, but the development of fiber-reinforced siding (such as Hardi-board) has eclipsed wood materials. Where wood siding exists on historic structures, borate treatment (such as Bora-Care) may be effective for up to 12 years.
We never would have suspected that insulation would be susceptible to termites, but it seems they will destroy anything in their path. There are now expanded polystyrene insulation boards with built-in termite resistance (disodium octaborate) for moist environments. If the material gets wet briefly, it may dry without losing its insulative capacity. This material is being used as crawlspace or basement insulation, so long as the insulation is kept a minimum of 3” below the sill plate.
We also had termites enter through a penetration at the shower drain. These less-visible locations can be difficult to monitor for termite activity, and the solution is to use a stainless steel mesh barrier around piping. Similar to a termite shield, the mesh stops termites from entering through openings that are 0.66 by 0.44 millimeters, and the material is too hard for them to chew through. However, they can create mud tubes to seek other entry points.
In order to reduce termites’ ability to nest in the ground adjacent to buildings, sand or basaltic termite barriers create a chemical-free barrier of particles that are large enough that termites cannot move them, and small enough to fill gaps so termites cannot crawl between them. These barriers can be installed below and around the foundation or slab, but only over soil is stable and compacted. The drawbacks include: soils that expand when wet (including clay-ey river deltas) are likely to create gaps in particle barriers; introducing landscaping can present problems; and the basaltic material may be cost-prohibitive, unless you live in Hawaii.
The best termite offense is a good defensive perimeter: soil treatment, mesh and soil barriers, and insect- and water-resistant materials. And if you need a termite-resistant building envelope – well, let’s just say we’ve learned a few lessons.