Screens and Other Deterrents for Birds, Rodents, and Other Pests

    Scope Images
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    Birds may nest in unprotected vent openings
    Birds may nest in unprotected vent openings
    Scope

    Design the home and install deterrents to discourage birds, rodents, and other pests from perching or nesting in or around openings in homes.

    • Design simple roofs and use metal step and valley flashing and leaf guards over gutters to discourage the build up of nesting materials and/or rotting of roofing materials that could provide harborage or entry for animals.
    • Design the home with sloped rather than horizontal ledges, columns headings, fixtures, etc., to discourage nesting and perching.
    • Install corrosion-proof wire mesh screening with ¼ inch or smaller holes over all vent openings unless the vent provides air to an air handler.  
    • Use sturdy soffit vent covers that are mechanically attached to framing to resist displacement by high winds and animals.
    • Install a stainless steel chimney cap with screening to keep out birds, animals, snow, and rain and to keep in fireplace embers.

    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 Single-Family New Homes, and EPA Indoor airPLUS.

    Description

    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 (Figure 1). If they get into a home’s HVAC system, allergens and contaminants can quickly be dispersed throughout the home.

     

    Birds may nest in unprotected vent openings
    Figure 1. Birds may nest in unprotected vent openings (Courtesy of Rocky Point Bird Observatory). 

    Pests can enter through surprisingly small openings (Figure 2).

     

    What mesh opening size is needed to keep out what type of pests?
    Figure 2. What mesh opening size is needed to keep out what type of pests? (Source: Building Out Bugs: Weep Holes).

     

    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. 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.  Crawlspace vents are another common entry point for animals. A bonus of installing screens and filters is that these materials may also block the entry of embers originating from fires.

    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 (Figure 3). 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, also known as wire mesh, can be used to prevent rodents from entering the home.
    Figure 3. Hardware cloth, also known as wire mesh, can be used to prevent rodents from entering the home (Source: National Parks Service 2014). 

     

    • 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.
    • Other materials used as shields, guards or barricades to discourage pests include concrete, brick, and aluminum and galvanized sheet metal (See Table 1).

    Table 1. Rodent-Resistant Construction and Exclusion Materials (Source: Geiger and Cox 2012). 

     

    Material

    Uses

    Thickness

    Concrete

    Slabs, curtain walls, foundation walls, ground cover barriers

    ≥ 2 inches (5.1 cm) if reinforced, or 3.75 inches (9.5 cm) if not reinforced

    Brick

    Curtain walls, facades to ground-level

    3.75 inches (9.5 cm) thick with joints filled with mortar

    Galvanized sheet metal

    Wall or pipe barriers

    24 gauge or heavier

    Kick plates or door edging

    22-gauge or heavier

    Perforated or expanded sheet metal grills

    14-gauge

    Hardware cloth

    Wire mesh to exclude rats

    if woven, 19-gauge, 1/2 x 1/2-inch (1.3x1.3-cm) mesh

    Mesh to exclude mice

    24-gauge, 1/4x1/4-inch (0.6x0.6-cm)

    Aluminum

    Frames and flashing

    22-gauge

    Kick plates and guards.

    18-gauge

     

    Design and Installation Tips to Discourage Roosting and Nesting by Birds and Other Animals

    • Design roofs that are simple; avoid gables, dormers, and roof-wall junctures that can form nesting and hiding spots for birds and other animals.
    • Install metal step flashing at all roof-wall junctures and in roof valleys to reduce the likelihood of vegetative debris collecting where it can create nesting spots. Metal valley flashing installed over peel-and-stick membranes also protects roofing materials from rotting and creating weak spots where animals can enter the attic.
    • Choose designs for exterior structures like decorative screens, moldings and lattices, siding, awnings, window sills, signs, fire sprinkler pipes, and column capitals with sloped tops that minimize opportunities for bird perching, roosting, or nesting, especially near building entrances. Use smooth materials and avoid horizontal surfaces. Slope window ledges and projections at 45 degrees to minimize bird perching and roosting.
    • Choose light fixtures with sloping surfaces rather than horizontal surfaces to deter bird roosting and nesting.
    • Cover attic and crawlspace ventilation openings and windows with woven or welded galvanized hardware cloth, screen, or filters to prevent entry by rodents, birds, and bats. 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.

    • Use sturdy soffit vent covers that are mechanically attached to framing  or blocking every 12 inches to resist displacement by high winds and animals. If the vent openings are larger, install hardware cloth behind them or replace with narrow metal louvered grates.

    • 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.

    • Install bird stop in the open ends of rounded roof tiles.

    • Install leaf guards on gutters to minimize collection of leaves, branches, and other nesting materials.
    • Screen in openings in buildings, exposed rafters in porch roofs, and other likely perches in semi-enclosed areas with rust-proof ¾-inch wire or plastic mesh to exclude birds or ½-inch metal mesh to exclude rodents.
    • Install bird spikes, "porcupine wire," netting, or similar devices to discourage birds from nesting on light fixtures or use bird exclusion devices, including wires, springs, nets, and electrical strips, to prevent birds from reaching light fixtures and other perching spots. (Note these devices are not foolproof and do require maintenance.)
    • Cover clothes dryer exhaust duct openings with opening gravity louvers. Do not install screens over dryer exhaust duct terminals. 
    • Mouse-proof interior residential air return grilles by placing 1/4-inch (0.6-cm) hardware cloth behind the grille.

    See the guide Reduce Pest Intrusion for more detailed information and a more far-reaching discussion of avoiding pests.

    Ensuring Success

    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. 

    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). Corrosion-resistant stainless steel termite shields should be installed at the top of foundation walls beneath the sill plate to discourage termite entry.

    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
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    Right - A durable, vented cover is installed over this exhaust duct to prevent bird and pest entry
    Right - A durable, vented cover is installed over this exhaust duct to prevent bird and pest entry
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    Right – The termination of this kitchen exhaust duct is sealed to the wall to keep out air and water and is screened to keep out pests.
    Right – The termination of this kitchen exhaust duct is sealed to the wall to keep out air and water and is screened to keep out pests.
    Image
    Right: Brick veneer is flashed correctly with weep holes and a fine mesh screen is installed to prevent pest entry.
    Right: Brick veneer is flashed correctly with weep holes and a fine mesh screen is installed to prevent pest entry.
    Image
    Mesh screen is correctly installed and gaps are less than 0.5 in.
    Mesh screen is correctly installed and gaps are less than 0.5 in.
    Image
    Ventilation air inlets provided with rodent / insect screen with ≤ 0.5 inch mesh
    Ventilation air inlets provided with rodent / insect screen with ≤ 0.5 inch mesh
    Image
    Mesh screen is spaced wider than 0.5 in. allowing insects to enter
    Mesh screen is spaced wider than 0.5 in. allowing insects to enter
    Image
    Mesh screen is spaced wider than 0.5 in. allowing insects to enter
    Mesh screen is spaced wider than 0.5 in. allowing insects to enter
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    Right – Bug screening keeps out insects and pests, allowing homeowners to enjoy the porch year round.
    Right – Bug screening keeps out insects and pests, allowing homeowners to enjoy the porch year round.

    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.

     

    ENERGY STAR Single-Family New Homes, Version 3/3.1 (Rev. 11)

    National Rater Field Checklist

    7. Dwelling Unit Mechanical Ventilation Systems (“Vent System”) 45 & Inlets In Return Duct 46
    7.7 Air inlet location (Complete if ventilation air inlet location was specified on design report; otherwise check “N/A”): 54, 55​
    7.7.1 Inlet pulls ventilation air directly from outdoors and not from attic, crawlspace, garage, or adjacent dwelling unit.
    7.7.2 Inlet is ≥ 2 ft. above grade or roof deck; ≥ 10 ft. of stretched-string distance from known contamination sources not exiting the roof, and ≥ 3 ft. distance from dryer exhausts and sources exiting the roof. 56
    7.7.3 Inlet is provided with rodent / insect screen with ≤ 0.5 inch mesh. 

    Footnote 45) As defined by ANSI / RESNET / ICC Std. 301-2019, a Dwelling Unit Mechanical Ventilation System is a ventilation system consisting of powered ventilation equipment such as motor-driven fans and blowers and related mechanical components such as ducts, inlets, dampers, filters and associated control devices that provides dwelling-unit ventilation at a known or measured airflow rate.

    Footnote 46) Item 7.3 applies to any outdoor air inlet connected to a ducted return of the dwelling unit HVAC system, regardless of its intended purpose (e.g., for ventilation air, make-up air, combustion air). This Item does not apply to HVAC systems without a ducted return.

    Footnote 54) Ventilation air inlets that are only visible via rooftop access are exempted from Item 7.7 and the Rater shall mark “N/A”. The outlet and inlet of balanced ventilation systems shall meet these spacing requirements unless manufacturer instructions indicate that a smaller distance may be used. However, if this occurs the manufacturer’s instructions shall be collected for documentation purposes.

    Footnote 55) Without proper maintenance, ventilation air inlet screens often become filled with debris. Therefore, EPA recommends, but does not require, that these ventilation air inlets be located so as to facilitate access and regular service by the occupant.

    Footnote 56) Known contamination sources include, but are not limited to, stacks, vents, exhausts, and vehicles.

    Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in in your state.

     

    DOE Zero Energy Ready Home (Revision 07)

    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.

     

    EPA Indoor airPLUS (Revision 04)

    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.

     

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

    Section R806.1 specifies that ventilation openings having a least dimension larger than ¼ inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl, or other similar material for smaller openings and that required ventilation openings shall open directly to the outside air and shall be protected to prevent the entry of birds, rodents, snakes and other similar creatures.

    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

    SCOPE

    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.

    DESCRIPTION

    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.

    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)
    Cassie Krejci,
    John Muncaster
    Organization(s)
    TERM Barriers by Polyguard Products
    Publication Date
    Description
    An article describing a way to protect drain and ventilation holes in brick veneer siding against pest. Selecting a fine screen mesh opening (1/55-inch or 0.5-mm) is important to guard against small insects such as subterranean termites.
    Author(s)
    Extension
    Organization(s)
    Extension Foundation
    Publication Date
    Description
    Website providing information about how to prevent rodent entry in homes.
    Author(s)
    Cooperative Extension Service
    Organization(s)
    U.S. Department of Agriculture Cooperate Extension Service,
    New York State Department of Environmental Conservation,
    Cornell Cooperative Extension
    Publication Date
    Description
    Web-based manual providing guidance for removal and preventing entry of nuisance wildlife.
    Author(s)
    Northeastern IPM Center
    Organization(s)
    Northeastern IPM Center
    Publication Date
    Description
    Website providing information on all types of pest management for multi-family housing.
    Author(s)
    Building Energy Codes Program
    Organization(s)
    DOE
    Publication Date
    Description
    Fact sheet explaining code-compliant methods for dealing with pests.
    Author(s)
    NREL
    Organization(s)
    NREL
    Description
    The Standard Work Specifications (SWS) are a tool for industry guidance to ensure effective, durable, and safe work is performed during home upgrades.
    *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 Measures
    Building Science-to-Sales Translator

    Corrosion-Proof Screened Vents =

    Image(s)
    Technical Description

    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.


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