Insect resistance of foam building insulation board: this article illustrates and describes the causes of risk of wood destroying insect attack (like termites or carpenter ants) on buildings using foam foundation or wall insulation.

Note that the insect risk associated with foam insulating board details (or any building design and product) varies by geographic location and the types of insect pests that are or are not present. Therefore good construction details to avoid insect damage must suit local requirements and meet local building codes.

Foam Insulation Products and Risk of Wood Destroying Insect Damage: termites, carpenter ants, etc.

The following comments pertain regardless of whether the foam insulation products we are addressing are sprayed foam insulation or solid foam insulating boards or panels. Sketch of common foam insulating board details courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Photo: a foundation and floor slab installation in Minneapolis, Minnesota, using blue foam insulation board under and around the slab. By encasing the foam completely in concrete we think that the installer was avoiding a potential attack path for carpenter ants or other wood-destroying insects.

[Click to enlarge any image]

• Wood destroying insect effects of foam insulation: 
  
  foam insulation is not an insect barrier; while these materials do not provide food for termites, they are easily penetrated by termites or carpenter ants (as are other insulating materials).
  
  For this reason our opinion is that it is bad design to bring foundation insulating foam panels up into contact with building wood framing materials unless an approved insect barrier has also been installed.
  
  What can we do to improve the insect resistance of buildings where solid foam board or foam spray foundation insulation are being applied?
  • Chemical barrier that resists insect attack:
    
    is applied around and under the building. Chemical barriers for termites and other wood destroying insects used to work very well, but modern chemicals may be less effective/less durable over time due to changes in pesticides to make these chemicals less of an an environmental hazard.
    
    See TERMITE SHIELDS vs TERMITICIDE.
  • Mechanical barrier that resists insect attack: 
    
    a metal shield is set atop all wood sills, extending an inch or more past the building interior and exterior wall surfaces, bent on an angle downwards to shed water, with exact details specified by a pest control officer and installed during construction.
    
    A termite shield may be effective but remains a risky approach to bug-proofing if the shield is not inspected and if not kept visually accessible on both inside and outside of the buildings for periodic check - a termite mud tube might bypass a metal shield.
    
    See TERMITE SHIELDS vs TERMITICIDE.
  • Good architectural design to resist insect attack: 
    
    the best wood destroying insect resistant-building design is to keep wood and other insect-friendly materials at least 8" above ground, provide no protected path for insect entry into the structure (such as behind solid insulation boards)
  • Building maintenance to resist wood destroying insect attack: 
    
    keep surface water and roof spillage away from the building perimeter. Do not pile up leaves, organic debris, wood piles, or mulch against building walls. Hire a professional to inspect the building, especially at high-risk points.

Because insect damage on buildings is very often related to locations of water leaks or moisture traps, readers should also

see WATER ENTRY in BUILDINGS.

...

Continue reading at TERMITE SHIELDS vs TERMITICIDE or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see

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• CARPENTER BEES - attacking polyurethane foam trim
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