- Sand Barriers
- Metal Termite Shields
- Monitoring, Detection and Identification
- Termite Treatment
Non-toxic termite control is the use of termite prevention and control without chemical use. Instead, physical controls are installed during construction such as sand barriers or metal termite shields. If termite infestation does occur, least toxic methods of treatment are used.
Most areas of Texas have termites. These include subterranean termites that live in the soil and drywood termites that attack dry wood. According to the Texas Agricultural Extension Service, there is a greater than 70 percent probability that wooden structures in Texas will be attacked by termites within 10 to 20 years. Termite problems within one year after construction have been reported.
When wood is used as a building material, termite prevention in the form of treated wood or naturally resistant wood will be required by building codes. Typically, chromated copper arsenate (CCA) pressure-treated wood is used. Two alternative chemical substances have gained popularity as more toxic substances such as chlordane have been banned for soil treatment. These include organophosphates and pyrethroids. However, these chemicals are toxic to people as well as termites, and can offgas and leach out into the soil and water table. They can be absorbed through the skin, lungs and through ingestion. Exposure to small children, workers, chemically-sensitive individuals and animals can lead to serious health problems.
Less toxic wood treatments are available. (See Wood Treatment Section.) However, alternatives to wood treatment and chemical treatment can be quite effective. Least-toxic strategies must be used in combination to achieve maximum effectiveness. Few pest control managers expect non-toxic methods to completely replace chemical use. However, they offer considerable potential for the reduction of chemical use, and may prevent such use in all but extreme situations.
|sand barrier, termite shields|
|Satisfactory in most conditions|
|Satisfactory in Limited Conditions|
|Unsatisfactory or Difficult|
Research and monitoring is underway to test the effectiveness of non-toxic termite prevention techniques. The USDA Southern Forest Experiment Station in Gulfport, Mississippi, and the University of Hawaii are doing research. Successful laboratory results have been obtained with the use of properly designed sand barriers. Pest control professionals in California have adapted and tested sand barriers with good results. Some studies in California have found some physical barriers to be 15% more effective than chemical treatments.
There are architects and pest management companies in Austin that can provide expertise and services in non-toxic termite prevention and control. However, not all professionals currently have knowledge or experience with non-toxic termite control.
Initial costs of non-toxic termite prevention may be 25% higher than chemical controls. However, these costs may be offset due to the long term nature of structural solutions. In addition, cost offsets can occur if traditional fill material is replaced with sand or cinder barriers, preventing the need for termiticides.
Lenders will typically look for traditional methods for the prevention of termites, such as the use of treated wood. Educating lenders about the effectiveness of non-toxic prevention measures and encouraging financing incentives for their use is a goal of the Green Builder Program.
For successful termite prevention using non-toxic methods, education and cooperation between the professional and the resident/owner will be necessary. Increased monitoring after construction will be necessary.
Building codes (such as Section R-310 of the CABO One and Two Family Dwelling Code) call for protection by chemical soil treatment, pressure-treated wood, naturally termite-resistant wood (such as heartwood of redwood and eastern red cedar), or physical barriers approved by the building official in areas with subterranean termites. Approved combinations of methods may be used.
For decay prevention, any wood (siding, trim, framing) within 6 inches of the finished grade must be protected. Additionally, wood girders within 12 inches, wood structural floor within 18 inches, and wood sills on masonry slabs within 8 inches must also be protected. Decay prevention and termite protection are addressed jointly with wood treatment and naturally resistant wood. Structural controls for termites such as sand barriers and termite shields will not eliminate the need for decay prevention in wood within the distances from the ground mentioned above.
The Honolulu building code was rewritten in 1991 to include the use of sand barriers instead of chemical controls. The City of Austin will examine precedents accepted by other jurisdictions on a case-by-case basis.
Any pest management program that uses the principles of Integrated Pest Management (IPM), or least toxic methods, will have the following components:
- Integration of least-toxic treatment methods and materials;
- Detection and identification.
No method of termite treatment can be assumed to be 100% effective. In homes with wood as a construction material, regular inspections should be performed, regardless of treatment and prevention methods. The best method is non-toxic prevention, however there are also non-toxic treatment methods if termites are found.
The only sure prevention of termite problems is the use of building materials other than wood. However, if wood is used, there are preventative measures available to the builder other than chemical treatments and treated wood products. A common tree in Austin known to resist termites is the familiar mountain cedar (actually a member of the juniper family). Although not commercially lumbered, natural cedar posts have traditionally been used as foundation piers on old structures, and extensively for fences and furniture. The use of juniper wood has some potential for application as a termite and insect resistant wood.Eliminating sources of chronic moisture in the home is one of the most important factors in managing subterranean termites, carpenter ants, and some wood boring beetles. Moist soil is necessary for termites to survive. Termites travel back and forth between soil and food sources because they must obtain moisture from the soil. In addition, capillary action and water vapor buildup can result in excessive dampness which can actually wick through a concrete slab or masonry foundation to the wood framing above it, thus attracting termites.
In above-ground foundations, moisture barrier films such as 6 mil polyethylene can be used to cover the area under the structure. This will help decrease moisture buildup in sub-flooring. Foundation wall vents should be placed to provide cross ventilation for homes with crawl spaces. If re-grading or remodeling covers vents, additional vents may be needed. Some experts recommend the use of moisture barriers under slab foundations as well.
Soil should always be from 6 to 18 inches below any wood member, the greater the distance, the better. Good siting and drainage design will help to prevent moisture buildup in and around the structure. All exterior grades should slope away from the structure to provide drainage. Porches and features such as planter boxes should be constructed and sealed to prevent moisture and soil contact with the structure.
Exterior landscaping should not cause moisture build-up around the foundation. A small air space should be retained between plant leaves and walls to prevent moisture and mold build-up. Automatic irrigation heads should be properly aligned or shielded to prevent direct spray onto the building.
Areas subject to moisture build-up, such as bathrooms, should be given special attention since they are likely to be attack areas. Areas under tubs and drains leading to the exterior (such as air conditioner drains) should be considered vulnerable spots.
All wood-to-soil and wood-to-concrete contacts should be eliminated for fence and deck posts, rail supports, and trellises etc. Posts should be placed in metal holders (commercially available). Even treated deck piers may not deter termites since they may bypass the treated piers to reach untreated decking above.
All wood subject to moisture, especially exterior wood, should be properly sealed. Exterior windows, even if under an overhang such as a porch, should be completely moisture sealed. Exterior siding, especially along the bottom wall edges, should be completely moisture sealed on all exposed surfaces.
All lumber scraps, wood debris and stumps should be removed from the site after construction is complete. Backfill under a foundation should never contain wood scraps, and scrap should never be left in crawlspaces or under foundations. Such scraps are invitations to termites to eat first the scrap and then move on to the main structure.
2.0 Sand Barriers
Sand barriers for subterranean termites are a physical deterrent because the termites cannot tunnel through it. Sand barriers can be applied in crawl spaces under pier and beam foundations, under slab foundations, and between the foundation and concrete porches, terraces, patios and steps. Other possible locations include under fence posts, underground electrical cables, water and gas lines, telephone and electrical poles, inside hollow tile cells and against retaining walls.
Sixteen grit sand or cinder is placed in a 20-inch band on the soil surface or in trenches next to foundation walls. The sand layer should be 4 inches thick at the foundation, and feathered out to meet grade at the outer edge of the 20-inch band. For trench installations, trenches should be 4″ deep and 6″ wide.
Some integrated pest management experts have developed a machine, called a sand pump, that blows sand under the house. For sand barriers around the outside perimeter of a foundation, they recommend a sand trench in order to avoid disturbance of the sand. In addition, a cap made of masonry or other materials may be recommended to protect the barrier from gardening, animals, etc. Tamping of sand can be done to increase impermeability to termite attack.
2.1 Slab Barriers
Termites can easily pass through small cracks, as small as 1/32″, which may occur in slab foundations. For sand barriers in conjunction with slab foundations, the sand or cinder must be applied before the foundation is poured. Installing the sand layer of the appropriate mesh size followed by a layer of coarser gravel for grading to the desired level has worked well. To cut costs, sand treatments may be installed in particularly vulnerable areas of the slab, such as around pipe penetrations, as opposed to under the entire slab.
Costs for cinder fill under a slab can often be competitive with the costs of standard fill and the initial chemical termite treatment.
2.2 Sand Selection
The size of sand particles is critical to the success of sand barriers. Sand or grit size should be no larger or smaller than that able to sift through a 16-mesh screen. Sand smaller than 16-grit can be carried away by termite workers; larger sand can support tunnel construction by termites. If the sand to be used has some particles smaller than 16-mesh size, sand can be screened with mesh of the appropriate size. Certain grades of sandblasting sand which come in bags may be suitable for barriers. Crushed volcanic cinder of the appropriate size is recommended by some experts.
Sand barriers can also be used to repair seals that have become broken between foundations and other building elements such as porches. Such settling and breaking of “cold” joint seals can occur due to subsidence and temperature extremes. In laboratory tests, sand was shown to retain its “seal” against structural members after movement similar to earthquakes. Although earthquakes are not a problem in our area, soil movement and settling due to expansive soils is often a problem.
Use of sand barriers is still experimental, and must be followed with post-installation as well as regular inspections. Sand barriers may cost 25 % more than conventional chemical treatments, however the physical barrier will provide long term protection. Chemical prevention is normally guaranteed for only one year, and introduces toxins into the home environment.
3.0 Metal Termite Shields
Metal termite shields are physical barriers to termites which prevent them from building invisible tunnels. In reality, metal shields function as a helpful termite detection device, forcing them to build tunnels on the outside of the shields which are easily seen. Metal termite shields also help prevent dampness from wicking to adjoining wood members which can result in rot, thus making the material more attractive to termites and other pests.
Metal shields are used in conjunction with concrete or solid masonry walls, and are fabricated of sheet metal which is unrolled and attached over the foundation walls. The edges are then bent at a 45 degree angle. Metal shields must be very tightly constructed, and all joints must be completely sealed. Any gaps in the seals will allow an entry point for termites. Joints may be sealed by soldering, or with a tar-like bituminous compound.
Metal flashing and metal plates can also be used as a barrier between piers and beams of structures such as decks, which are particularly vulnerable to termite attack.
4.0 Monitoring, Detection and Identification
The Bio-Integral Resource Center (see Resources, General Assistance) recommends the following steps:
- Monitor the building at least once per year.
- Identify the species of termite.
- Correct structural conditions that led to the infestation.
- Apply physical or biological controls.
- Spot treat with chemicals if necessary.
- Check for effectiveness and repeat if required.
Regular termite monitoring should be done with a plan of the structure in hand. This will help to identify inaccessible areas that may be hard to spot with a visual inspection. Annual or bi-annual inspections are recommended.
Subterranean termites build characteristic mud tubes for movement between nests. The appearance of these tubes are often the first sign of infestation. Detection can become difficult if such tubes are hidden inside walls, or termites are entering in cracks occurring in concrete slabs or foundations.
Dogs are being used by some individuals to aid in termite inspection. These dogs are trained to detect termites and other wood damaging insects, and can provide information about inaccessible areas of the structure. Their keen sense of smell coupled with their ability to wriggle into areas too small for human access can make the dog-assisted inspection a valuable tool.
5.0 Termite treatment
The first step in any termite treatment is accurate identification of the species. Next, location of nests must be found. Next, selection of a combination of least toxic strategies and tactics is necessary.
When selecting a pest management company, be sure to choose a reliable firm. Texas law requires commercial pesticide applicators to be certified. Check for certification documentation, references, and work experience, or check with the Structural Pest Control Board of Texas. Ask if the company practices integrated pest management techniques, or has an experimental license which may be necessary for some alternative techniques.
Non-toxic treatments include use of nematodes (microscopic worms), especially for chemically-sensitive individuals or environmentally-sensitive areas. Nematodes are pumped into the infested area, where they will kill the insects. Boric acid bait blocks can be placed around the structure, where they will attract the pests to consume termiticides without broad application of chemicals. Drywood termites can be treated with thermal, freezing, or electrical eradication techniques. Desiccating dusts, non-toxic substances resulting in pest dehydration and death, have also been used successfully on drywood termites.
These treatments can be combined with others, such as installing metal shields (if they have not been used previously), sealing of broken seals or open areas, and re-grading of soil outside the foundation to improve drainage or create a gap between soil and wood areas such as siding. In addition, termites can be physically removed by trapping or nest excavation.