Pest-Resistant Ground Cover at Foundation Perimeter

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    Concrete (4 inches thick at 5% slope) provides a pest-resistant perimeter around the foundation
    Scope

    Discourage pests by creating a ground break around the entire perimeter of the building at the foundation to limit the availability of food, water, and shelter for pests.

    • Provide a 2-foot-wide ground break of pea gravel, crushed stone, graded basalt particles, concrete pavers, or a concrete skirt.
    • Keep bushes and trees at least 3 feet from the home.
    • Direct irrigation spray away from the walls and foundation.
    • Plant drought-resistant plants.
    • Do not over-irrigate.
    • Control surface water – slope the ground away from the building’s perimeter on all sides.
    • Direct rainwater from gutters and downspouts away from the building.
    • Provide outdoor storage (garage, shed, etc.) to encourage homeowners not to store items outside next to the foundation where they can provide harborage and cover for pests.
    • Provide a hard surface or gravel area to store garbage cans located where they will not be touching the house.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home programENERGY STAR Single-Family New Homes, and Indoor airPLUS.

    Description

    Pests include insects and animals that have a harmful effect on humans, food, or living conditions. Pests include insects, termites, cockroaches, spiders, dust mites, snakes, rodents, birds, bats, etc. when these animals become unwelcome intruders in the home.

    The first strategy is to keep pests out of the home by creating a ground break around the entire perimeter at the building foundation to limit the availability of food, water, and shelter.

    Provide a 2-foot-wide layer of pea gravel or crushed stone extending from the foundation around the perimeter on all sides of the home. Alternative pest-resistant ground breaks such as graded basalt particles, concrete pavers, or a poured concrete skirt are also effective. These ground covers should be 4 inches deep and sloped at a 5% grade away from the structure.

    Bushes and trees near a home provide food, a living place, and sheltered passage for pests such as rats, mice, birds, cockroaches and ants. Keep the branches of bushes and trees at least 3 feet from homes. If squirrels are a problem (and also in wildfire areas), tree branches should be at least 6 feet from the structure.

    Pooling water anywhere around the home can be an attractant for a variety of pests. Minimize the likelihood of pooling water with the following steps:

    • Control surface water – slope the ground away from the building’s perimeter on all sides (Figure 1).
    • Direct rainwater from gutters and downspouts away from the building (Figure 2).
    • Direct irrigation spray away from walls and foundation.
    • Provide drought-resistant plants.
    • Do not over-irrigate.

    Trash and clutter around the home, especially leaning against or touching the foundation or exterior walls, can provide shelter and cover for pests. Minimize the likelihood of this by providing the following for homeowners.

    • Provide outdoor storage (garage, shed, etc.) to encourage homeowners not to store items outside next to the home’s foundation where they can provide harborage and cover for pests.
    • Provide a hard surface or gravel area to store garbage cans where they will not be touching the house.
    • Screen in areas under decks with 1/8-inch metal screening or solid walls to keep animals from nesting under the deck. This will also reduce the wildfire danger of debris collecting under the deck where it could be fuel for fires from blowing embers.

    To control surface water, slope the ground away from the building perimeters on all sides
    Figure 1. To control surface water, slope the ground away from the building perimeters on all sides (Source: Building Science Corporation)

     

    Gutters and downspouts direct rainwater down and away from buildings to keep building walls and foundations drier
    Figure 2. Gutters and downspouts direct rainwater down and away from buildings to keep building walls and foundations drier (Source: Building Science Corporation).

     

    Pea Gravel or Crushed Stone as a Perimeter Pest-Resistant Ground Break

    Figures 3 and 4 and Photographs 1 and 2 illustrate the use of a 2-foot-wide perimeter ground break of pest-resistant pea gravel or crushed stone. The thickness of the pea gravel or crushed stone layer should be a minimum of 4 inches. The pea gravel or crushed stone ground break should slope away from the building at a grade of approximately 5% (1/2 inch per foot).

    A layer of pea gravel or crushed stone, 4 inches thick and sloped 5%, provides a pest-resistant ground break around the perimeter of a slab foundation
    Figure 3. A layer of pea gravel or crushed stone, 4 inches thick and sloped 5%, provides a pest-resistant ground break around the perimeter of a slab foundation (Source: Building Science Corporation).

     

    A layer of pea gravel or crushed stone, 4 inches thick and sloped 5%, provides a pest-resistant ground break around the perimeter of a basement foundation
    Figure 4.  A layer of pea gravel or crushed stone, 4 inches thick and sloped 5%, provides a pest-resistant ground break around the perimeter of a basement foundation (Source: Building Science Corporation)

     

    Crushed stone provides a pest-resistant perimeter around the foundation
    Photograph 1. Crushed stone provides a pest-resistant perimeter around the foundation (Source: Building Science Corporation). 

     

    Pea gravel provides a pest-resistant perimeter around the foundation
    Photograph 2. Pea gravel provides a pest-resistant perimeter around the foundation (Source: Building Science Corporation)

     

    Concrete Skirt as a Perimeter Pest-Resistant Ground Break

    Photographs 3 and 4 illustrate the use of a 2-foot-wide perimeter concrete skirt ground break. The thickness of the concrete skirt should be a minimum of 4 inches. The concrete should be cast on a 4- inch-=thick stone capillary break. Control joints should be provided every 4 feet. In Climate Zones 5 and  higher the concrete should be air entrained to a minimum of 5 percent at a compressive strength of 3,500 psi in order to resist freeze-thaw damage. The concrete skirt ground break should slope away from the building at approximately 5% (1/2 inch per foot).

    Concrete (4 inches thick at 5% slope) provides a pest-resistant perimeter around the foundation
    Photograph 3.  Concrete (4 inches thick at 5% slope) provides a pest-resistant perimeter around the foundation (Source: Building Science Corporation).

     

    A concrete skirt provides pest resistance at the building perimeter
    Photograph 4. A concrete skirt provides pest resistance at the building perimeter (Source: Building Science Corporation)​​​

     

     

    Concrete pavers set in 4 inches of sand provide a pest-resistant ground break at the building perimeter
    Photograph 5. Concrete pavers set in 4 inches of sand provide a pest-resistant ground break at the building perimeter (Source: Building Science Corporation

     

    Curtain Walls and Other Burrowing Rat Deterrents

    In areas where burrowing rats are an issue, consider the following steps:

    • Use crushed stone rather than pea gravel, with stone pieces 1-inch (2.5 cm) diameter or larger, laid in a band at least 2 feet (60 cm) wide and 6 inches deep.
    • Use "curtain walls" around and below a crawlspace foundation where necessary to keep out burrowing rats (see Figure 5). Construct vertical curtain walls that extend from the above-grade exterior of the wall down 2 feet below the surface and out 8 to 12 inches horizontal to form an "L" shaped flange directed away from the building to prevent rats from burrowing under foundations. Curtain walls can be constructed of 29-gauge corrugated iron, concrete, or bricks.

    For additional recommendations, see the Solution Center guide “Reduce Pest Intrusion.” Also see Pest Prevention by Design by Geiger and Cox (2012).

     

    Construct a vertical curtain wall of 29-gauge corrugated iron, concrete, or bricks that extends down 2 feet and out 8 to 12 inches to prevent rats from burrowing under crawlspace foundations
    Figure 5. Construct a vertical curtain wall of 29-gauge corrugated iron, concrete, or bricks that extends down 2 feet and out 8 to 12 inches to prevent rats from burrowing under crawlspace foundations (Source: Geiger and Cox 2012).

     

    Ensuring Success

    Consult a licensed architect or engineer to develop the detailed approach for pest resistance. The pest-resistant design can occur in conjunction with thermal efficiency and rainwater/groundwater control design details where the approaches are complimentary rather than incompatible.

    Climate

    Pests

    Rodents, birds, various insects, and other pests are present throughout the United States.

    Termites are prevalent in the central and southern United States (see termite infestation map).

    Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7)
    Figure 1. Termite Infestation Probability Map, Adapted from the 2021 International Residential Code (IRC), Figure R301.2(7) (Source: Courtesy of PNNL). 

     

    Right and Wrong Images
    Image
    A layer of pea gravel or crushed stone, 4 inches thick and sloped 5%, provides a pest-resistant ground break around the perimeter of a slab foundation
    A layer of pea gravel or crushed stone, 4 inches thick and sloped 5%, provides a pest-resistant ground break around the perimeter of a slab foundation

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

     

    2009, 2012, 2015, 2018, and 2021 International Residential Code (IRC)

    Section R202 defines Termite Resistant Material as pressure-preservative-treated wood in accordance with the AWPA standards in Section R317.1 in the 2018 and 2021 IRC (R318.1 in 2009, 2012, and 2015 IRC), naturally durable termite-resistant heartwood of species such as Alaska yellow cedar, redwood, Eastern red cedar and Western red cedar including all sapwood of Western red cedar, steel, concrete, masonry or other approved material.

    Sections R318.1 – R318.3 describe control methods including field-applied chemical treatments for soil and wood and metal or plastic barriers including shields on top of foundation walls. Section R318.4 notes that in areas indicated as having a very heavy probability of termite infestation, as shown in the termite probability map in 2021 IRC Figure R318.4 (R301.2(7) in 2018 IRC, R301.2(6) in 2009, 2012, and 2015 IRC), rigid foam including extruded or expanded polystyrene, polyisocyanurate and other foam plastics should not be installed on the exterior face of foundation walls or under foundation walls or slabs below grade and, if foam is applied on exterior above-grade walls, there must be at least six inches of clearance between the foam and the soil surface. There are exceptions to this restriction: if all structural members of the building are made of noncombustible or pressure-preservative-treated wood, or the foam is protected by some approved method, or if the foam is installed on the interior of basement walls.

    Figure R318.4 in the 2021 IRC (R301.2(7) in 2018 IRC, R301.2(6) in 2009, 2012, and 2015 IRC) is a Termite Infestation Probability Map, determining if the home will be constructed in an area of very heavy, moderate-to-heavy, slight-to-moderate, or none-to-slight termite infestation.

    Section R403.1.6 states that sill plates and sole plates shall be protected against decay and termites where required by sections R317 and R318.

    Section N1102.9 (N1102.2.10 in 2018 and 2015 IRC, N1102.2.9 in 2012 IRC, and N1102.2.8 in 2009 IRC) notes that slab-edge insulation is not required in jurisdictions designated by the code official as having a very heavy termite infestation probability.

    Retrofit:  2009, 2012, 2015, 2018,  and 2021 IRC

    Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)

    Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

    Existing Homes

    The approach and details provided in this guide apply to both new and existing homes.

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    Lstiburek,
    Brennan
    Organization(s)
    Building Science Corporation,
    BSC
    Publication Date
    Description
    Report describing steps homeowners can take to improve the indoor air quality in their home, including ventilating, preventing pests, and reducing pollutants in the home.
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

    Building Science Corporation

    Pacific Northwest National Laboratory

    Last Updated

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