Termites In Rigid Board Insulation

Termite infestations in buildings that have rigid board insulation are a growing problem in the southeastern United States. In this two-part series, Clemson University researchers assess the problem and recommend solutions.

Riddle: What can save you a bundle and cost you a small fortune at the same time?

Answer: Rigid board insulation when it is installed as a superhighway for termites.

With a surge in the use of rigid board insulation (RBI) over the last decade, there has been an equivalent surge in termite infestations associated with its use. Due to some of the more common insulation installation practices, the ability of pest control operators to effectively inspect and treat structures for termites is limited when rigid board insulation (RBI) is placed as a continuous sheet below grade. In recent literature, termite problems in RBI have been identified as a serious problem.

Foam board or rigid board insulation is used with good reason. One of the most common uses of RBI is as a perimeter sheathing placed along the exterior of foundation walls against the masonry structure. The insulation, including materials such as polystyrene and polyisocyanurate, has excellent properties and characteristics which make them ideal candidates for improving energy efficiency of structures.

However, as with most products that seem too good to be true, RBI is no exception. RBI can create a scenario in which subterranean termites, along with other insects, use the insulation as a pathway to gain hidden entry into the wooden members of a structure.

The use of RBI in construction has increased from 1985, when approximately 5% of buildings contained some RBI (Christian 1990), to 1992, when 50% of new buildings used RBI. The noted increase stems from low cost, good energy saving characteristics, excellent thermal properties, and high strength-to-weight ratios (Strzepek 1990).

But with these advantages come disadvantages. The strength and hardness of RBI can be affected by termite excretions (Building Research Station 1966) with potentially severe termite damage occurring to polystyrene (Gay & Wetherly 1969) and styrene resins (Shimizu et al. 1970). RBI does not appear to serve as a source of nutrition for termites since it is not passed through the digestive tract, but damage occurs from bitten-off fragments that are either incorporated into tunnels or discarded (Hicken 1971).

The problem with this type of perimeter insulation is increased by the addition of skin coats such as stucco or siding (aluminum, vinyl, wood, etc.), which hide the RBI from view and limit detection. RBI is also being placed under slabs and is used as form board into which concrete foundation is poured directly. When RBI is placed in direct contact with the soil it creates the same conducive circumstances as wood in contact with the soil.

In an effort to warn their member companies, the National Pest Control Association (NPCA) issued guidelines recommending that PCOs not accept jobs in which termite-conducive RBI problems cannot be corrected (Kramer 1993). This bold move by NPCA should send a signal to all PCOs to cautiously enter into contracts on homes with poorly placed RBI.

PCO SURVEY. In an effort to assess the termite/rigid board insulation problem in South Carolina, we developed a mail survey sent to a sample of 225 pest control companies belonging to the South Carolina Pest Control Association (SCPCA). At the time of this survey the association had 315 member companies and there were a total of 775 companies operating in the state of South Carolina.

Surveys requesting information for termite inspections and treatments conducted during 1993 were mailed in February 1994, and follow-up letters were sent at one, three, and eight weeks as reminders to return surveys. The questions covered four main areas:

• Demographics.

• Occurrence of RBI.

• Prevalence of RBI and structural damage.

• Treatment of structures when RBI was present.

There was an excellent response to the survey, with an 83% return on the 225 surveys mailed. Of those, 173 (77%) surveys represented respondents who conduct termite inspections or treatments. The data reported here are based on the responses from these companies. Not all survey questions will be discussed.

• Demographics. Most respondents to the survey were owners (73%) or managers (17%) of the pest control company surveyed. Since people in either of these positions have access to all company records, we felt the information they provided was accurate. Most companies (82%) had fewer than five technicians. However, these smaller companies performed 82% of all reported termite treatments.

• Occurrence of RBI. RBI on structures inspected or treated for termites was reported by 34% of the companies. Of these, 81% of the companies reported up to 10% of the structures they treated or inspected for termites had RBI, and 2% reported greater than 75% of the structures having RBI. With 59% of the companies reporting RBI installed below grade, we predict an increase in termite/RBI problems in the future.

• Prevalence of RBI and Structural Damage. Of the 34% reporting RBI, 81% of the companies reported termite damage to RBI installed above grade in up to 10% of the structures they inspected, and 72% of the companies reported damage to RBI installed below grade in up to 10% of the structures. Nine percent of the companies reported termite damage to RBI installed below grade in greater than 75% of the structures (see Table 1 below).

FREQUENCY OF DAMAGE
ABOVE GRADE		BELOW GRADE
OCCURENCE %	% OF TIME SEEN	OCCURENCE %	% OF TIME SEEN
1-10	81	1-10	72
11-25	15	11-25	11
26-50	42	26-50	4
51-75	0	51-75	5
76-100	0	76-100	9
Table 1: Percentage of the time termite damage to rigid board insulation was seen on structures (above and below grade) by survey respondents, by frequency of occurrence.

Termite damage to wooden structural members in the presence of RBI installed both above and below grade was significant. In up to 10% of all structures reported in this survey, 81% of the responding companies reported above grade damage and 72% reported below grade damage. Location of termite damage on a structure in the RBI or in wooden structural members was variable and not limited to any one location. However, RBI damage was documented most often between grade and footings (42%), and between grade level and sill plate (22%). Structural damage was most often reported just above grade level (20%), between grade level and footings (29%), and between grade level and sill plate (29%). The amount of damage in wooden members was positively correlated with the amount of damage seen just below grade, between grade and sill plate, and above the sill.

Twenty-five percent (25%) of the companies reported damage to RBI due to insects other than termites. Carpenter ants were the most frequently reported at 87%, but other insects such as solitary wasps in the family Sphecidae and beetles in the family Dermestidae were reported. This indicates that RBI is subject to damage on a wider scale than previously thought. Carpenter ants, for example, may be of importance from Northern California into British Columbia or in the Northeastern United States, where termite pressure is not as intense as in the Southeast.

• Treatment of Structures When RBI is Present. Treatment for termite control in the presence of RBI should be approached cautiously. In our survey, companies chose not to treat structures with RBI 57% of the time for a variety of reasons (see Table 2 below). Primarily they either determined the conducive circumstances were not correctable or treatable (34%), or they could not provide a guarantee for treatment (45%).

TO TREAT OR NOT TO TREAT
CHOSE TO TREAT: 43%	CHOSE NOT TO TREAT: 57%
METHOD USED %	REASON PCO CHOSE NOT TO TREAT %
Treated as they would any other structure and provided a guarantee. 24	Insulation created a situation conducive to infestation that was not treatable or correctable. 34
Treated but did not provide a guarantee. 33	Could not guarantee the treatment. 45
Removed insulation below grade, then treated. 31	Reasons other than those listed above. 21
Did something other than above options. 12
Table 2: Treatment options and the percentage of survey respondents who chose to treat structures versus those who chose not to treat structures.

Other reasons for not accepting a job when RBI was present (21%) included:

1) The customer did not want insulation removed.

2) The company gave the job to a competitor.

3) The PCO recognized the difficulty of treatment due to prior experience.

The companies (43%) that did choose to treat structures with RBI approached treatment in different ways. Nearly a quarter of the companies (24%) treated as they would any other structure and provided a guarantee, but more companies (33%) treated as usual without offering a guarantee. Other companies (31%) went to great lengths to remove insulation below grade to correct the problem, then treated.

Other approaches to treatment (12%) included:

1) Trenched out below the insulation prior to treatment, then backfilled.

2) Cut insulation off above grade then sealed bottom of insulation.

3) Recommended that a qualified builder replace insulation with a product not conducive to termite infestation and check the structure for soundness.

4) Treated only if RBI was not below grade.

5) Modified guarantee such that company was not responsible for damage as a result of hidden entry through RBI.

6) Treated only because they had "won" a bid.

7) Pretreated and only discovered later that RBI was installed.

The economic impact of damage to RBI and the structure is unknown, but in situations where termites are detected the cost of correction and repair are presumed to be at least equivalent to any energy savings that would have been realized. One South Carolina home was documented to have nearly $200,000 worth of termite damage hidden by RBI.

• Litigation. Of all the data gathered from this survey, the most disturbing finding is that 12% of the respondents have been involved in litigation due to termite damage hidden by RBI. Companies who were the sample for this survey belong to the SCPCA and are among the best in the country. Past experience with many of these companies demonstrates they are dedicated and skilled at their work, and thus are far less likely to find themselves in court for poor inspection and treatment practices.

• Model Energy Code. The Model Energy Code (MEC) is the standard building code for most of the country (Council of American Building Officials 1992). It mandates that RBI be placed around and under slab-on-ground floors. The MEC also mandates that RBI be placed not only in contact with the soil, but as deep as 3 feet below grade to reach beyond the frost line in parts of the country with colder winters. It is the continuous nature of the RBI that creates a termite-conducive situation.

• Recommendations. The best recommendation we can offer at this time when RBI has been placed in a continuous fashion on the perimeter of a structure is to remove a 6-inch strip just above grade. This vision strip or inspection gap provides the PCO visual access to the structure for a proper inspection. Without the ability to see termite shelter tubes, the PCO has very little chance of identifying a problem before a swarm occurs. It is important to realize that removal of RBI may not be possible if it has been placed behind steps, a porch, a patio or other inaccessible area, so these situations should be handled with particular caution when a warranty is provided.

Admittedly there will be an economic loss due to the thermal break (thermal short-circuit) caused by removing RBI, but the amount of damage potential due to termites is greater, particularly in the southeastern United States where termite pressure is immense. We recognize the value of RBI and its significant merit in keeping the cost of housing and energy affordable. RBI is a great insulator. We support and encourage its continued use for perimeter insulation if builders provide for a standard termite inspection. PCT

Brian C. Smith and Patricia A. Zungoli are with the Urban Entomology Research Laboratory, Clemson University, Clemson, S.C. Funding for this project was provided by DowElanco, the South Carolina Pest Control Association, and the South Carolina Agricultural Experiment Station. The authors wish to thank the members of the South Carolina Pest Control Association who participated in the survey. Kevin Hathorne and Terry Pizzuto of Clemson University provided technical support and Hoke S. Hill provided statistical guidance.

REFERENCES

Building Research Station (Watford, UK) Overseas Division. 1966. Plastics in Building. Overseas Building Notes. 108: 1-9.

Council of American Building Officials. 1992. Model Energy Code. Council of American Building Officials, Leesburg, VA. 87 pp.

Gay, F. J. and A.H. Wetherly, 1969. Termite Resistance of Plastics V. CSIRO, Canberra.

Guyette, J.E. 1994. Termites Targeting Foam Insulation. Pest Control. 62(2): 49,50,52.

Hicken, N.E. 1971. Termites: a world problem. Hutchinson & Co. Ltd., London, 233 pp.

Kramer, R.D. 1993. Foam Insulation and Termites. Service Letter ESPC 055075, Number 1284. National Pest Control Association, Inc. Dunn Loring, VA. 3 pp.

SAS Institute. 1985. SAS users guide: statistics. SAS Institute, Carey, NC. 956 pp.

Shimizu, K., Y. Nakashima, and A. Sakanoshita. 1970. Studies on termite damage to a synthetic high polymer. Bulletin of the Faculty of Agriculture, Miyazaki University. 17: 281-285. (English summary only)

Strzepek, W.R. 1990. Overview of physical properties of cellular thermal insulations, pp. 121-140 in Insulation Materials, Testing, and Applications. McElroy, D.L. and J.F. Kimpflen (eds). American Society for Testing and Materials, Philadelphia. 759 pp.