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Plant Industry - Structural Pest Stucco and Termites

FOAM INSULATION AND TERMITES

Certain building techniques have become popular in the past few years which use foam insulation at or below grade (below the soil). Smith & Zungoli (1995) and Clemson University report that this type construction can make termite protection and control very difficult. In many cases, foam insulation below grade (below ground) is as detrimental as direct wood to earth contact. Current common building methods which are a problem when foam is below grade include:

insulation forms made of foam (polystyrene, polyisocyanurate or similar products) between which concrete foundation walls are poured,
rigid board foam which extends below grade
chambers of foam within concrete blocks.

Smith & Zungoli also report that foam insulation in contact with the ground makes termite inspection, treatment, and prevention very difficult. Buildings constructed with foam insulation at or below grade cannot be properly inspected or treated for control of subterranean termites for the following reasons:

Foam insulation at or below grade provides the structure with ground contact that termites use to reach the wood undetected.
While termites do not eat foam insulation, they are able to tunnel through it in order to get to the wood in the structure.
A termite infestation inside foam insulation is often not visible to a homeowner or a pest control operator during a pest control inspection, until swarming and severe damage to the wood of a structure has occurred. Foam insulation installed behind stucco makes termite infestations even more difficult to detect.
To date, research has been inconclusive regarding the efficacious incorporation of pesticides into foam, during the manufacturing process.

FOAM INSULATION AND GROUND CONTACT

Building techniques using foam insulation have been around since the early 1980s. By 1992, it was estimated that 50 percent of new buildings use some form of foam insulation. Foam insulation has excellent thermal qualities, making it a good choice for energy conservation. For this reason, foam insulation typically is used on the outside of a concrete slab or block foundation, to form up a concrete slab, in hollow concrete blocks, and in expansion joints (where two concrete slabs meet). Problems with termite infestations arise when the foam insulation is placed as a continuous sheet with portions of it resting below grade (below ground). In the past, basic termite biology has been ignored in use of these materials below grade. Termites can use the below-grade foam insulation as a pathway into the structure by tunneling through the foam, or between the foam and masonry. Because insulation is hidden from view by aluminum, vinyl siding, wood, paint, stucco, etc. the termites can remain undetected until severe damage has occurred. For this reason, any energy savings that foam insulation helps to achieve can be negated by the cost of termite damage to the structure. Waterproofing or coating the foam insulation will not keep termites out.

Brian Smith and Pat Zungoli in a 1995 publication in Pest Control Technology magazine recommended that where foam insulation extends below grade that a six inch gap be created in the foam insulation. The insulation should be cut at ground level and again six inches higher. This would allow for an adequate termite inspection. In 1997, Georgia building codes were changed to require a six inch clearance between foam insulation and the soil and prohibit the installation of foam insulation below grade. This codes affects construction begun after October 1997.

IMPROPERLY INSTALLED SYNTHETIC STUCCO
MAY CREATE A MOISTURE PROBLEM

Synthetic stucco, an acrylic polymer which is applied over a fiberglass mesh, is an increasingly popular exterior wall finish that uses foam insulation. Recent reports from the pest control industry, the building industry, and local television news stations have indicated that there are some unique aspects of the installation of this wall system that may allow moisture damage if not properly finished. The mesh covers foam insulation board, which is attached to gypsum sheathing board, plywood or a masonry wall. The gypsum sheathing and the plywood are nailed to wood framing. The glass fiber mesh is then coated with a base coat and a finish coat of acrylic, to resemble stucco.

Wafer board, also known as oriented strand board (OSB), is recommended in the construction of synthetic stucco walls, due to a tendency to absorb water, according to a spokesperson for an Exterior Insulation and Finish Systems (EIFS) manufacturer. EIFS also states that, if used, the gypsum sheathing that has a glass mat, rather than paper surface, is preferred.

The debate with the synthetic stucco wall system hinges on whether moisture enters the synthetic stucco through small cracks in the surface of the stucco and/or through cracks around poorly caulked windows, doors, sealed joints and flashings. Nevertheless, once behind the synthetic stucco surface, water is trapped due to the low permeability of the synthetic stucco and the foam insulation. This creates two potential problems. Increased moisture favors development and growth of wood destroying fungi. Under certain circumstances, termites may form an aerial colony in the structure when sufficient moisture is available. In this situation, the termites will continue to feed on the structure even after contact with the soil is broken. Aerial colonies may be more difficult to locate and control than below ground or subterranean infestations of termites.

A builder familiar with decay and correction of synthetic stucco problems should inspect the structure to determine if water is getting behind the stucco-like finish. Appropriate caulking or sealing measures should then be taken.

^{Useful Links}

^{Florida Entomologist:

http://www.fcla.edu/FlaEnt/fe78p507.html}

¹Information taken from "Use of Foam Insulation Below Grade May Encourage Termites: A Guide for Builders and Homeowners". Spring, 1996. Clemson University Department of Pesticide Regulation.

Smith, B.C. and P. A. Zungoli. 1995. Termites in Rigid Board Insulation: Part 1. Pest Control Technology 23(10): pages 68, 69, 72-74

Smith, B.C. and P. A. Zungoli. 1995. Termites in Rigid Board Insulation: Part 2. Pest Control Technology 23 (11): pages 56, 65-66.

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