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Exterior Insulated Foundations Need Termite Protection
A recent Toolbase Technote from the NAHB Research Center provides builders who are using exterior foam insulation for slab-on-grade, crawl-spaces and frost-protected shallow foundations with techniques that can be used to help prevent termite infestations.
Although the insulation is not a source of food for the insects, termites can tunnel through it to reach cellulose or the wood structure and they can be difficult to detect, the technical note advises. With an impenetrable exposed surface like concrete, the termites are more likely to build mud tunnels on the exterior of the wall when coming up from the soil to the wood framing members, making them easier to spot.
Much of the U.S. is prone to termites, from Florida to Connecticut and all points to the west, and the areas with the heaviest infestations are those where slab-on-grade or crawlspace foundations are typical, the note says. This can sause a dilemma for builders who want to use foam to enhance the thermal performance of their homes.
In some areas where there is a very high probability of termite infestation, installing exterior foam plastics can be limited by building codes. Where infestation is more moderate, the decision about how best to protect homes against serious termite damage is initially up to the builder, and after that it is left to the home owner to continue with a long-term program.
“Correct installation of the selected system(s), regular inspection and maintenance, and good building details are the best defense against termites and assurance of a long-lived home,” the note says. However, no one approach guarantees that a structure will be termite-proof, and it will best serve as a deterrent or as a method of detecting the presence of termites before they can inflict any real damage.
For builders using exterior rigid foam insulation on slabs, termite barriers should be considered to reduce the probability of infestation.
Physical barriers impeding the movement of the insects into the structure can include flashings between the foundation and the wood structural elements, waterproof membranes, aggregate mixtures under and around the foundation and stainless steel mesh.
Flashings are the most practical physical barriers, the note says, and although they may not prevent termites from finding their way to a home’s wood structural members, they will at least force them to the outside of the home, where their tunnels can be detected.
Chemical barriers can also be effective, although they need to be maintained. They work for only about five years at the most. Their primary downside is the environmental impact of the chemicals. Also, replenishing the chemicals is not entirely easy or effective, unless a reticulation system — a piping system to distribute the termicide — has been installed during construction, the note advises.
Baiting systems have been found to be quite effective if they are properly installed and maintained, and they are more environmentally friendly because they require only limited amounts of termiticide.
The note provides a list of simple construction and site management rules that should be followed to control moisture and termite food supply near the foundation:
- Grading must have a slope of at least 5% for the first 10 feet from the building on all sides.
- Driveways, patios and masonry walks that intersect the foundation should have a minimum 2% slope away from foundation.
- If the home is not designed with large — 2 or more feet — overhangs at the eaves, gutters and downspouts should be installed.
- Downspouts and sump pump water must discharge 3 or more feet from the building.
- Sprinkler heads should be located 2 or more feet from the house and adjusted so that water does not hit the building while operating.
- Condensate line(s) must discharge 2 or more feet from the building and be located 5 or more feet from the dryer vent.
- There must be no wood debris, either scraps from construction or remains of removed trees, in the backfill.
- Plants and turf must be at least 2 feet from the foundation.
- Organic mulch is not recommended within 2 feet of the foundation.
- Wood fences or decks that abut the house should be pressure-treated.
- All pipes, wiring and conduits that penetrate a slab at grade or masonry within 12 feet of grade should be sealed.
- Chemical and/or physical termite barriers should be installed.
- Home owner instructions should be posted near the water heater, electrical panel or furnace describing how to maintain the home to reduce the threat of termite infestation by controlling moisture and having annual termite inspections.
The technical note provides more information about the products that can be used, with a couple of links to more details on flashing for exterior foam insulation on slabs. To read the note, click here.
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