figure 4-6

Figure 4-6. Slab-on-Grade Termite Control Techniques

Techniques for controlling the entry of termites through residential foundations are necessary in much of the United States (see Figure 4-6). Consult with local building officials and codes for further details.

  1. Minimize soil moisture around the foundation by surface drainage and by using gutters, downspouts, and runouts to remove roof water.
  2. Remove all roots, stumps, and wood from the site. Wood stakes and form work should also be removed from the foundation area.
  3. Treat soil with termiticide on all sites vulnerable to termites (Labs et al. 1988).
  4. Place a bond beam or course of solid cap blocks on top of all concrete masonry foundation walls to ensure that no open cores are left exposed. Alternatively, fill all cores on the top course with mortar. The mortar joint beneath the top course or bond beam should be reinforced for additional insurance.
  5. Place the sill plate at least 8 inches above grade; it should be pressure-preservative treated to resist decay. Since termite shields are often damaged or not installed carefully enough, they are considered optional and should not be regarded as sufficient defense by themselves.
  6. Be sure that exterior wood siding and trim are at least 6 inches above grade.
  7. Construct porches and exterior slabs so that they slope away from the foundation wall, are reinforced with steel or wire mesh, usually are at least 2 inches below exterior siding, and are separated from all wood members by a 2-inch gap visible for inspection or a continuous metal flashing soldered at all seams.
  8. Fill the joint between a slab-on-grade floor and foundation wall with liquid-poured urethane caulk or coal tar pitch to form a termite and radon barrier.

Plastic foam and mineral wool insulation materials have no food value to termites, but they can provide protective cover and easy tunneling. Insulation installations can be detailed for ease of inspection, although often by sacrificing thermal efficiency.

In principle, termite shields offer protection, but should not be relied upon as a barrier. Termite shields are shown in this document as a component of all slab-on-grade designs. Their purpose is to force any insects ascending through the wall out to the exterior, where they can be seen. For this reason, termite shields must be continuous, and all seams must be sealed to prevent bypass by the insects.

These concerns over insulation and the unreliability of termite shields have led to the conclusion that soil treatment is the most effective technique to control termites with an insulated foundation. However, the restrictions on widely used termiticides may make this option either unavailable or cause the substitution of products that are more expensive and possibly less effective. This situation should encourage insulation techniques that enhance visual inspection and provide effective barriers to termites. For more information on termite mitigation techniques, see NAHB (2006).