Install screening to keep birds, rodents, and other pests out of vent openings in homes.
- Install corrosion-proof wire mesh screening with ¼ or smaller holes over all vent openings unless the vent provides air to an air handler.
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.
Birds, rodents, bats, and insects can carry bacteria, viruses, parasites, fungi, and allergens that can cause illnesses to home dwellers. If they get into homes, attics, basements, or ducts, they can also cause considerable property damage. If they get into a home’s HVAC system, allergens and contaminants can quickly be dispersed throughout the home. Pests can enter through surprisingly small openings. Gaps as small as 1/4 inch (the width of a pencil) are enough for mice to squeeze through into the wall cavity or interior of the house.
All vents and duct openings for heating and air conditioning should be covered with durable metal screens to prevent animal entry. To prevent pest entry, cover ventilation openings and windows with woven or welded galvanized hardware cloth, screen, or filters to prevent entry by rodents, birds, and bats. Windows can be covered with fine-mesh screen to prevent entry by flying insects.
For large openings or where the screen may be subject to abuse, add crossbars to support the hardware cloth. If the opening must be accessible, install the screen on a hinged frame.
Interior residential cold air return grills can also be mouse-proofed by placing 1/4-inch (0.6-cm) hardware cloth behind the grille.
Caution: Hardware cloth less than 1/2 x 1/2 inch (1.3 x 1.3 cm) significantly reduces air flow. In some locations, small-mesh screens can become clogged with dust or freeze over. Hardware cloth covering air handler intake vents should not be less than 1/2 x 1/2 inch (1.3 x 1.3 cm), unless the covering is recommended by the manufacturer. Instruct the homeowner to periodically clean the screen.
Materials and Installation
Screening used to prevent pest entry should be made of a durable moisture-resistant, gnaw-resistant material. The following recommendations are from Best Practices for Nuisance Wildlife Control: A Training Manual, prepared by the Cooperative Extension Service.
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.
Stainless steel or vinyl-coated hardware cloth is stronger than galvanized and will never rust. The disadvantages of stainless steel are that it is 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 to keep out larger animals is 1×1-inch mesh, while ½×½-inch mesh is suitable for most smaller animals, except mice, which require 1/4×1/4-inch mesh.
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 hardware cloth or metal louvered grates to these soffit vents to prevent entry through these 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.
See the guide Reduce Pest Intrusion for more detailed information and a more far-reaching discussion of avoiding pests.
Inspect to verify that screening materials are present in all vents and openings, that screens are made out of rust-resistant durable materials, and that screening is securely mechanically fastened in place to prevent removal by pests.
No climate-specific information applies.
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.
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.
3.2 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.
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 all building openings in the existing home that can’t be sealed (ventilation system intakes and exhaust outlets, attic vent openings, etc.)
If any openings are found to be lacking corrosion-proof wire mesh screening with ¼-inch or smaller holes, install screening as described in the Description tab.
See the U.S. Department of Energy’s Standard Work Specifications for more on preventing pest entry and infestation.
Protect vent openings from bird and pest entry with durable, securely fastened screening as described in the Description tab.
If birds, bats, rodents, or other pests are already present in the vent openings or attic, consult a nuisance wildlife control operator for the appropriate removal procedures.
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.
The following authors and organizations contributed to the content in this Guide.
Rodent-resistant vent screens are used to cover all vents except the clothes dryer vent with insect screening to help keep out larger pests and insects. These screens consist of metal wire mesh with openings of a half-inch or less.