Seal all penetrations in the foundation wall and at joints between the foundation and exterior above-grade walls. Seal all cracks around plumbing and wiring penetrations and cover with metal flashing. Take additional precautions in moderate to heavy termite areas including using solid concrete or filled concrete block at the top of foundation walls, reinforcing concrete slabs and walls to mininimize cracking, and using treated wood or metal sill plates. Take additional precauations in very heavy termite areas including not installing foam plastic insulation under slabs or on the exterior of below-grade walls, and keeping foam plastic insulation at least 6 inches above the final grade on exterior walls and at least 3 inches below the sill plate on interior conditioned crawlspace walls.
See the Compliance Tab for related codes and standards and criteria to meet the requirements of national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and EPA Indoor airPLUS.
Insects, rodents, and other pests are more than just a nuisance; they can carry diseases, aggravate allergies, and spread germs and they can cause considerable property and structural damage if their activities go undetected for any length of time. Fortunately, many of the air sealing and water management measures associated with energy efficiency and high performance, also help with keeping pests outside of the home.
Mice can squeeze through holes as small as ¼ inch and rats can enter holes as small as 5/8 inch. Rodents can chew through spray foam, wood, and some types of plastic. As a general practice, seal all holes that are greater than 1/4 inch by 1/4 inch with corrosion-resistant copper or stainless steel wire mesh to prevent entry by rodents, birds, and bats. Smaller holes can be caulked to seal out insects. To keep insects from getting into walls through air gaps behind siding or draining vents in brick walls, block their entry with wire screens. Seal all cracks around plumbing and wiring penetrations and cover the seal with escutcheons or metal flashing. Do not leave a rough surface that will trigger rodents’ instinctual response to start chewing. Do not leave blown foam exposed to the sun. Exposure to the sun will break it down and insects and rodents may nest in the foam.
For the gap under doors, install door sweeps that touch the ground and go the entire length of the bottom of the door. If properly installed, the sweep will brush the ground, but not hold the door open (a fire hazard). In areas prone to rodent infestation, do not use vinyl sweeps.
Making a house resistant to the entry of pests minimizes both the damage they can cause and the exposure of occupants to pest-related allergens, diseases, and asthma triggers. While the use of chemicals and poisons are common conventional methods for preventing or treating pest infestations, relying on their use increases ongoing maintenance activities and costs for the homeowner and they can contribute to health and safety concerns of their own. There are several steps that builders can take to reduce opportunities for pest intrusion and damage, without relying on chemicals.
Wet wood attracts carpenter ants and is easier for animals to gnaw through so it is important to construct the home so that it stays dry or dries out quickly if some components do get wet. The Building America Solution Center has several guides to help builders properly manage water drainage around the site and foundation; these can be accessed through the ENERGY STAR Water Management System Builder Checklist. The steps that builders take to seal the building envelope to prevent air leakage will also help to keep out insects and rodents. Several of these steps are described in the Building America Solution Center under the ENERGY STAR Thermal Enclosure System Rater Checklist, TES 5. Air Sealing.
In areas with a high likelihood of termite infestation, building codes restrict where and how rigid foam can be installed along the interior and exterior of basement and foundation walls. Although termites don’t eat the foam, they tunnel through it; therefore, its presence can hide their activities from building inspectors. Information about restrictions related to rigid foam is found in the guides Unvented Crawlspaces and Conditioned Basements and Rigid Foam Board Interior Insulation for Existing Foundation Walls. Precautions regarding the use of rigid foam insulation in termite-prone areas are listed below.
How to Reduce Pest Entry through Concrete Foundations
- Locate all seams, penetrations, and holes in concrete slab, concrete foundation walls, and at wall to slab seam. Brush away any loose dust or debris. Apply a generous and continuous bead of urethane caulk to any cracks, seams, or openings. See Figure 1.
- Reduce the likelihood of cracks in concrete by using concrete admixtures, welded wire fabric, reinforcing rods, or other technologies designed to reinforce the concrete and help prevent and control cracking. See Figure 2.
- Minimize seams with monolithic pours. Fill control joints with polyurethane caulk.
- If using concrete block foundation walls, make the top course solid block, filled block, bond beam, or masonry cap. See Figure 3.
- If a sump is installed, make sure it has an air-tight sump cover consisting of a mechanically attached cover with a full gasket seal. See the guide Gasketed/Sealed Sump Pump Covers.
- Install concrete or wire mesh curtain walls along crawlspace foundation walls; the curtain should extend 36 inches below grade.
Other Steps for Reducing Pest Entry
- Install pest barrier insect screening at the top and bottom of above-grade walls that have a ventilation gap behind the cladding. See Figure 4.
- Install metal flashing at the base of doors and a metal threshold under the doors; ensure that doors are tight fitting. Install self-closing doors. Install screen doors that have a heavy kick plate and a solid frame.
- Install solid blocking material around pipes to seal off holes.
How to Minimize Termite Entry
- Install physical barriers such as termite-resistant mesh over joints in foundation.
- Install termite-resistant barriers beneath the slab.
- Install termite shields between the foundation wall and the sill plate. Ensure that the metal is chemically compatible with the treated wood sill plate (many post 2004 non-arsenic wood treatments are corrosive to steel); or install sill seal or peel and stick membrane between the termite shield and the wood sill plate to prevent the metal from corroding.
- Choose the termite-resistant heartwood of durable species such as western red cedar, redwood, incense cedar, Port Orford cedar, black locust, northern white cedar, and Alaska cedar.
- See the Termite Infestation Probability Map, Figure R301.2(6) in the 2009 International Residential Code to determine the termite probability for your location and take the following additional precautions as necessary.
- If in areas classified as “Moderate to Heavy” on the termite infestation probability map, taking the following precautions:
- Foundation walls should be solid concrete or masonry with a top course of solid block, bond beam, or concrete-filled block.
- Interior concrete slabs should be constructed with 6 x 6 in. welded wire fabric, or the equivalent, and concrete walls should be constructed with reinforcing rods to reduce cracking.
- Sill plates should be made of metal or preservative-treated wood.
- If in areas classified as “Very Heavy” on the termite infestation probability map (i.e., Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and parts of California and Texas), take the following additional precautions:
- Foam plastic insulation should not be installed on the exterior face of below-grade foundation walls or under slabs.
- Foam plastic insulation installed on the exterior of above-grade foundation walls should be kept a minimum of 6 in. above the final grade and any landscape bedding materials and should be covered with moisture-resistant, pest-proof material (e.g., fiber cement board or galvanized insect screen at the bottom-edge of openings).
- Foam plastic insulation applied to the interior side of conditioned crawlspace walls should be kept a minimum of 3 in. below the sill plate.
- If in areas classified as “Moderate to Heavy” on the termite infestation probability map, taking the following precautions:
Clean areas to air seal prior to caulking to ensure a good seal. Inspect for air leakage afterwards, visually or with a blower door.
To ensure worker health, ventilation may be needed during the application of sealants and pest treatments.
Follow code requirements regarding the installation of foam insulation around foundations in termite-prone areas.
Consult the International Residential Code’s “Termite Infestation Probability Map” (2009 IRC Figure R301.2(6)) to determine if the home will be constructed in areas of very heavy, moderate-to-heavy, slight–to-moderate, or none-to-slight termite infestation. Additional precautions should be taken in areas classified Moderate to Heavy and Very heavy (see Compliance tab).
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.
Rater Field Checklist
4. Air Sealing (Unless otherwise noted below, “sealed” indicates the use of caulk, foam, or equivalent material).
4.1 Ducts, flues, shafts, plumbing, piping, wiring, exhaust fans, & other penetrations to unconditioned space sealed, with blocking / flashing as needed.
4.3 Above-grade sill plates adjacent to conditioned space sealed to foundation or sub-floor. Gasket also placed beneath above-grade sill plate if resting atop concrete / masonry & adjacent to conditioned space.26, 27
Footnote 26) Existing sill plates (e.g., in a home undergoing a gut rehabilitation) on the interior side of structural masonry or monolithic walls are exempt from this Item. In addition, other existing sill plates resting atop concrete or masonry and adjacent to conditioned space are permitted, in lieu of using a gasket, to be sealed with caulk, foam, or equivalent material at both the interior seam between the sill plate and the subfloor and the seam between the top of the sill plate and the sheathing. 27. In Climate Zones 1 through 3, a continuous stucco cladding system adjacent to sill and bottom plates is permitted to be used in lieu of sealing plates to foundation or sub-floor with caulk, foam, or equivalent material.
Footnote 27) Existing sill plates (e.g., in a home undergoing a gut rehabilitation) on the interior side of structural masonry or monolithic walls are exempt from this Item. In addition, other existing sill plates resting atop concrete or masonry and adjacent to conditioned space are permitted, in lieu of using a gasket, to be sealed with caulk, foam, or equivalent material at both the interior seam between the sill plate and the subfloor and the seam between the top of the sill plate and the sheathing.
Please see the ENERGY STAR Certified Homes Implementation Timeline for the program version and revision currently applicable in in your state.
Exhibit 1 Mandatory Requirements.
Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
Exhibit 1, Item 6) Certified under EPA Indoor airPLUS.
3.1 Minimize Pathways for Pest Entry.
- Seal all penetrations and joints between the foundation and exterior wall assemblies (ENERGY STAR requirement).
- Air seal all sump covers (ENERGY STAR requirement).
- When sealing larger gaps that provide potential points of entry for rodents, copper or stainless steel wool is recommended in addition to sealant.
- Additional precautions should be taken in areas classified as “Moderate to Heavy” termite infestation probability (as identified by 2015 IRC Figure R301.2 ):
- Sill plates should be made of metal or preservative-treated wood.
- Additional precautions should be taken in areas classified as “Very Heavy” termite infestation probability (as identified by 2015 IRC Figure R301.2) i.e., Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina and parts of California and Texas:
- Foam plastic insulation installed on the exterior of abovegrade foundation walls should be kept a minimum of 6 in. above the final grade and any landscape bedding materials and should be covered with moisture-resistant, pest-proof material (e.g., fiber cement board or galvanized insect screen at the bottom-edge of openings).
3.2 Rodent/Bird Screens for Building Openings. Provide corrosion-proof rodent/bird screens (e.g., copper or stainless steel mesh) for all building openings that cannot be fully sealed and caulked (e.g., ventilation system intake/exhaust outlets and attic vent openings).
Exception: This requirement does not apply to clothes dryer vents.
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 2009 IRC Figure R301.2(6) (R301.2(7) in 2018 IRC), rigid foam including extruded or expanded ploystyrene, 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.
Section N1101.3 (Section N1107.1.1 in 2015 and 2018, N1109.1 in 2021 IRC). 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 this code. (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.
Section R402.2.8 notes that slab-edge insulation is not required in jurisdictions designated by the code official as having a very heavy termite infestation.
Section R402.4 specifies that the home should be constructed to limit air leakage. Section 402.4.1 indicates specific areas to be caulked, gasketed, or sealed, including all joints, seams, and penetrations. Section 402.4.2 specifies that air leakage should be tested with an extensive visual inspection or with a blower door test with a maximum air leakage of <7 ACH 50.
Section R402.2.9 (R402.2.10 in 2015 and 2018 IECC) notes that slab-edge insulation is not required in jurisdictions designated by the code official as having a very heavy termite infestation.
Section R402.4 specifies that the home should be constructed to limit air leakage and should be blower door tested to confirm air leakage is <5 ACH 50 in Climate Zones 1-2 and <3 in Climate Zones 3-8. Table R402.4.1.1 specifies the installation of a continuous air barrier and notes specific air barrier details.
Section R101.4.3 (Section R501.1.1 in 2015, 2018, and 2021 IECC) 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 this code. (See code for additional requirements and exceptions.)
This Retrofit tab provides information that helps installers apply this “new home” guide to improvement projects for existing homes. This tab is organized with headings that mirror the new home tabs, such as “Scope,” “Description,” “Success,” etc. If there is no retrofit-specific information for a section, that heading is not included.
Inspect the perimeter of the existing home.
- Note that tree branches, gutters, anything leaning against the house, and all gaps, cracks, cavities, or open chases with access to the outside may give pests access to the house.
- Remove all materials touching the house, including tree branches and bushes.
- Note that damp wood encourages entry by insects and pests. Untreated wood should not touch the ground. To prevent water from pooling around the house ensure proper drainage, by sloping the grade away from the house 0.5 inch per foot for 10 feet on all the sides. See the guide Final Grade Slopes Away from Foundations for more information on water management.
Inspect the house foundations, including the inside of the crawlspace.
- See the Pre-Retrofit Assessment of Crawlspaces and Basements for guidance on avoiding moisture issues and for more information on pests.
Seal all holes, gaps, and cracks.
- See the Description tab for information on sealing foundations and slabs.
- Cover all stationary sealed holes, cracks, and gaps with escutcheon plates, wood, or metal coverings. Cover the cracks and holes on both the interior and exterior surfaces. Or stuff the holes with wire mesh and cover that with a hardening compound on both the interior and exterior surfaces.
- Install rodent-resistant door sweeps in rodent-prone areas.
- Do not use blown-foam sealant in areas exposed to the sun or in areas where it alone is expected to block rodent or insect entry or movement.
- Cover all openings with animal- and weather-resistant screens, one-way doors, self-closing louvers, or other coverings. Search the Building America Solution Center for more information on specific features such as chimneys, passive ventilation openings, open access under decks, porches, and cantilevers, and open access to crawlspaces.
See the U.S. Department of Energy’s Standard Work Specifications for more on preventing pest entry and infestation.
Sealing Cracks, Gaps, and Holes
Ensure that no untreated wood is in contact with both the ground and concrete foundations or any other part of the house. Cover exposed earth in crawlspaces and basements with a vapor retarder made of 6-mil polyethylene sheeting. All joints of the vapor retarder shall overlap by 6 inches and be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches up the stem wall and shall be attached and sealed to the stem wall. See the guide Capillary Break at Crawlspace Floors – Polyethylene Lapped up Walls and Piers or Secured in the Ground for more information.
Seal all holes, gaps, and cracks. Common points of rodent and insect entry include under poorly sealed doors and where pipes and wires go through walls. For utility penetrations, small gaps can be filled with foam, spackle, or caulking. Larger gaps will need reinforcement. Cover the hole with wood or a metal plate (escutcheon plates around pipes) or stuff the hole with wire mesh and cover that with a hardening compound. Cover the cracks and holes on both the interior and exterior surfaces of the building enclosure. Remove baseboards and seal the junction between the wall and the floor to stop insects from migrating from room to room, to help block entry from the outside under exterior walls, and to help improve energy efficiency. In multi-level structures, the junction between the walls and the ceiling should also be sealed. Use gaskets and caulk to seal light switch boxes, outlet boxes, and other cracks and penetrations.
Whatever materials are used to seal out rodents, make sure the final patch is smooth. An uneven surface will trigger a rodent to gnaw. Rodents use their whiskers to feel gaps where their bodies might fit. From there they gnaw and dig to make the gap big enough. If a rat or mouse’s skull can fit through a hole or gap, the rest of the body can squeeze through. A 1/4-inch hole is all that is needed for young mice and young rats can squeeze through a ½-inch hole.
Where rodent infestations have occurred or are likely, check the sweep on exterior house and garage doors. To see if the sweep is providing full coverage, stand inside the home or garage while it is daylight outside. Close the blinds or drapes and turn off the interior lights then see if any light shines through gaps at the bottom or lower corners of the door. If there are gaps under the door, install a new rodent-proof door sweep. Do not install a vinyl sweep as rodents can chew through vinyl. Instead, install a rodent-proof metal and rubber door sweep that touches the ground and goes the entire length of the bottom of the door. The sweep should extend completely to the corners. If properly installed, the sweep will brush the ground, but not hold the door open (a fire hazard). Some brands of door sweeps for rodent-prone areas include a stainless-steel strip attached to a thick bristled brush. You can also install a rubber seal along the bottom of the garage door to increase durability and discourage gnawing.
Cellulose Insulation with Boric Acid
Blown-in cellulose insulation is available that is treated with boric acid which acts as both a fire retarder and an insecticide [Integrated Pest Management Toolkit for Building Owners, Managers, and Staff]. Treated cellulose can be used to insulate several components of existing homes, including exterior walls, vented attics, overhangs, and floors over garages.
Covering Holes and Other Access Points
All holes, gaps, and cracks should be filled with durable, chew-resistant materials. All permanent openings like windows, vents, flues, etc., should be covered with grates or screens that are fastened in place and made of durable materials.
Galvanized sheet metal is durable and, when attached with screws, resistant to removal by raccoons and other animals. But it can be hard to bend and fit around corners.
Galvanized hardware cloth (or "metal mesh") is easier to shape than sheet metal and is reasonably durable. Hardware cloth is generally available in quarter-inch and half-inch mesh sizes. Half-inch hardware cloth is stronger but less flexible than quarter-inch. To keep smaller animals, such as bats or mice, out of an area, use quarter-inch hardware cloth. Hardware cloth is often used to create fences.
Stainless steel or vinyl-coated hardware cloth is stronger than galvanized and will never rust. The disadvantages of stainless steel are that it's much more expensive and harder to cut and shape.
Vinyl-coated, welded wire mesh is even stronger than hardware cloth. It lasts longer and will never rust (one manufacturer guarantees its product for seven years when used in the ocean), but it is more expensive than hardware cloth. Welded wire mesh is sold in rolls and is available in different heights, gauges, and mesh sizes. Some nuisance wildlife control operators prefer to use welded wire mesh to create rat walls and for any other installation that is meant to last a long time. The recommended size for larger animals is 1×1-inch mesh, while ½×½-inch mesh is suitable for most smaller animals.
Aluminum flashing is flexible and relatively easy to shape around corners. It is best for bird and bat exclusion because raccoons and rodents can usually chew or claw through it. Other exclusion materials include caulk, sealant (for movable joints), copper mesh (this resembles steel wool but doesn't rust), and expanding foam insulation. These materials are great for sealing cracks and other small openings.
To minimize the entry of flying insects, install screens on all operable windows and passive ventilation openings and install filters on all HVAC air intake ports. A bonus of installing screens and filters is that these materials may also block the entry of embers originating from fires.
Animals frequently enter buildings through vents. Replace damaged and vulnerable vents with sturdier, more animal-proof designs. Some vents can be modified with homemade screens. For example, you could attach quarter-inch hardware cloth to screen a kitchen hood vent or protect an attic fan. Just be careful that you don't reduce the amount of ventilation too much when you're modifying a vent, especially with dryer vents. This could increase the risk of fire. Check the requirements for each piece of equipment before you modify the vent.
Pop-up roof vents should be made of either metal or heavy-duty plastic. The best models are totally enclosed to prevent birds and rodents from nesting inside them. (See Figure 1.) There are also commercial stainless steel box screens that can be installed over existing vents.
Ridgeline vents are roof vents that extend along the entire ridgeline of the roof. (See Figure 2.) The screening over the vent openings should be durably fastened to the vent structure. The vents come with end caps that frequently work loose allowing small animals, such as sparrows, mice, and bats, to easily get inside attics. Replace the caps and secure to prevent entry into these vents.
A wide range of animals, from sparrows to raccoons, can find their way into a building through the ventilation openings located in the soffits under the eaves. Securely attach metal louvered grates over these soffit vent openings to prevent entry. (See Figure 3.)
Plastic gable louvers on the sides of buildings should be replaced with metal gable louvers. The gaps between individual louver slats should be narrow enough so birds can't nest in them. Screen the back (inside part) of the vent to keep bats and insects out of the attic.
Clothes dryer vents are another popular route to the indoors used by small animals. Be careful when screening these vents because lint buildup can damage the dryer and cause fires. Clean the screen frequently or choose a vent design that prevents lint build-up while still excluding animals. See the guide Proper Clothes Dryer Venting for more information.
Crawlspace vents are often missing or pushed aside to route clothes dryer vents or other wiring through the these holes in the foundation wall. Inspect all crawlspace vents, including those located under decks, and ensure that all are covered with ¼-inch metal screens that are fastened in place with permanent fasteners.
Sewer vent pipes can be covered with commercial shields to prevent rodents and birds from entering the building by slipping through gaps next to the pipes. (See Figure 4.)
Chimneys are attractive to raccoons, squirrels, bats, birds, and other animals that like to makes dens or nests in tree cavities. To keep animals out of a chimney, you should install a chimney cover. Find a model that meets fire codes. Most chimney covers are made of stainless steel or galvanized steel, but there are also copper and aluminum models. Some work both as a cover and a damper.
If your chimney has one flue and the flue is lined with a tile flue liner, look for a cover design that attaches to a single tile flue liner. These models generally bolt to the outside of the tile liner or have legs that slip inside the flue. Covers that slip inside the tile liner keep out squirrels and birds but raccoons can usually remove this kind of cover. If raccoons are a problem, choose a chimney cover that bolts to the sides of the flue. Choose models with the smallest openings allowed by fire codes to exclude bats.
Other chimney covers attach to, or around, the top of the chimney. These covers are very helpful if there are several flues in each chimney or if there are no tile liners extending through the top of the chimney.
There are commercial covers designed to fit metal chimneys. With care, you should be able to enclose the metal chimney cover with half-inch hardware cloth. Several chimney cover manufacturers are able to custom fit covers for unusual chimneys (for a price, of course). Call the manufacturer to find out which chimney measurements are needed.
Open Areas Under Decks, Porches, and Cantilevers, or Large Open Access to Crawlspaces
The fence design shown in Figure 7 is sometimes called a rat wall. It is often attached to a foundation, deck, or porch, or installed as a free-standing barrier around a garden area. Rat walls are effective against a variety of animals including skunks, woodchucks, raccoons, squirrels, and rats. Match the size of the mesh to the size of the animal you're trying to exclude.
The top of the fence is attached to a structure. The bottom is buried 6 to12 inches deep and includes a bottom edge or “shelf” that juts out about 6 to 12 inches to help stop animals from digging under the fence.
If there is evidence of animal activity prior to installation of the wall, one-way doors can be installed in the rat walls to allow the animals a pathway out. First, attach the rat wall. Leave one or two locations open and install one-way doors there. Make sure the animal can't dislodge or dig underneath the one-way doors. When there's been no sign of animal activity for several days, remove the one-way doors and complete the enclosure.
See Compliance tab.
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.
Insects, rodents, and other pests are more than just a nuisance; they can carry diseases, aggravate allergies, and spread germs. These pests can cause considerable property and structural damage if their activities go undetected for any length of time. There are several steps that builders can take to reduce opportunities for pest intrusion and damage. Wet wood attracts carpenter ants and is easier for animals to gnaw through so it is important to construct the home so that it stays dry or dries out quickly if some components do get wet. In areas with a high likelihood of termite infestation, building codes restrict where and how rigid foam can be installed along the interior and exterior of basement and foundation walls. Although termites don’t eat the foam, they tunnel through it; therefore, its presence can hide their activities from building inspectors. Many of the same activities that builders take to air seal a home, like caulking seams and sealing around pipes and wiring , will also keep out insects. Vent openings and ventilation gaps at the tops and bottoms of walls should be covered with wire mesh.