TERMITE AND WOOD DECAY CONTROL TECHNIQUES
Figure 2-8F. Termite Control Techniques for Basements, Footing Detail
Figure 2-8S. Termite Control Techniques for Basements, Sill Detail
Techniques for controlling the entry of termites through residential foundations are advisable in much of the United States (see Figures 2-8F and 2-8S). The following recommendations apply where termites are a potential problem. Consult with local building officials and codes for further details.
- Minimize soil moisture around the basement by using gutters, downspouts, and runouts to remove roof water, and by installing a complete subdrainage system around the foundation.
- Remove all roots, stumps, and scrap wood from the site before, during, and after construction, including wood stakes and formwork from the foundation area.
- Treat soil with termiticide, or deploy properly-maintained bait stations on all sites vulnerable to termites.
- Place a bond beam or course of 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, and reinforce the mortar joint beneath the top course.
- Place the sill plate at least 8 inches above grade; it should be pressure-preservative treated to resist decay. The sill plate should be visible for inspection from the interior. Since termite shields are often damaged or not installed carefully enough, they should not be regarded as sufficient defense by themselves.
- Be sure that exterior wood siding and trim is at least 6 inches above grade.
- Construct porches and exterior slabs so that they slope away from the foundation wall, and are at least 2 inches below exterior siding. In addition, porches and exterior slabs should be separated from all wood members by a 2-inch gap visible for inspection or by a continuous metal flashing soldered at all seams.
- Fill the joint between the slab floor and foundation wall with urethane caulk or coal tar pitch to form a termite barrier.
- Use pressure-preservative-treated wood posts on the basement floor slab, or place posts on flashing or a concrete pedestal raised 1 inch above the floor.
- Flash hollow steel columns at the top to stop termites. Solid steel bearing plates can also serve as a termite shield at the top of a wood post or hollow steel column.
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 exterior insulation systems. 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).