The best way to avoid problems with animals in your home, school or office is to prevent them from entering in the first place.
Before excluding an animal
Is it in or out?
Before closing animal entry sites in a building, be certain that animals will not be trapped inside. If you are uncertain whether an entry site is active, monitor it for at least two days. Placing newspaper in the hole, stapling cardboard over the hole, or placing duct tape over the hole works well. Animals that currently inhabit the building usually will need to be removed before proceeding with exclusion.
Time of year.
In winter, many animals (e.g., woodchucks, raccoons, chipmunks) are inactive for long periods. You may think that an entry hole is inactive only to be unpleasantly surprised in the spring or during a warm spell. Snow and ice also make it difficult to safely work on the outside of a building.
Watch for little ones!
During the spring and summer, the presence of young animals can complicate exclusion. Listen for sounds (such as high-pitched squealing or chirping) of the young in walls, fireplaces, etc. Another sign, if you can get close enough, are the teats of female mammals: they will usually appear enlarged and bare of hair when nursing. Although it is generally not illegal in New York State to remove young animals from buildings, special consideration should be given as to when and how it is done.
Keep it legal.
Building codes, fire codes, and other ordinances are important to keep in mind when deciding how to exclude animals. For example, many homemade chimney covers do not meet legal safety requirements.
Does it work?
The durability and effectiveness of a technique varies by species and situation. To illustrate, bats are generally not able to chew or claw their way through most exclusion materials. However, they are often persistent in finding small, over-looked holes. Raccoons and rodents, on the other hand, are capable of removing insufficient exclusion or opening new holes into a structure. Be sure your methods are appropriate to your situation.
How does it look?
Keeping aesthetics in mind, choose options that do not detract from the looks of the building. Efficacy, however, should not be sacrificed for attractiveness. Replacing damaged woodwork in a vulnerable location may look better without a metal covering but animals may quickly damage the wood again. Painting the metal can improve its appearance and keep the animals out.
Exclusion Materials and Procedures
Reducing an animal’s access to the structure can diminish future problems significantly.
- Trim trees back from the roof.
- Remove thick vegetation, debris, and firewood piles from near the foundation.
- Install barriers on transmission lines (check with your local utility company first!) to reduce squirrels’ access to the building.
- Eliminate nearby food supplies: pet food, garbage, compost, and bird seed, should be kept in locations or containers that are not accessible to problem animals.
Seal Structural Openings
You can use a variety of materials to close structural openings used by animals.
Galvanized sheet metal is durable and, when attached with screws, resistant to removal by raccoons and other animals. It can, however, be difficult to bend and fit unobtrusively around corners.
Galvanized metal mesh (known as hardware cloth) shapes more easily than sheet metal and is reasonably durable. Hardware cloth is generally available in quarterinch and half-inch mesh sizes. Half-inch hardware cloth is stronger but less flexible than quarter-inch. Quarter-inch is also more appropriate for smaller vertebrates, such as mice and bats. Hardware cloth is frequently used to prevent animals from going underneath the parts of buildings that lack foundations. The hardware cloth, or other appropriate fencing material, is attached to the bottom of the structure and buried into the ground. In general, the barrier fence (often referred to as a “rat wall”) should be buried one foot deep with a six-inch horizontal shelf at the bottom. The shelf will help prevent animals from digging underneath the barrier.
Stainless steel mesh and hardware cloth is stronger than galvanized and will never rust. X-cluder™ manufactures stainless steel mesh products for rodent exclusion. The disadvantages of stainless steel are that it is significantly more expensive and it is more difficult to cut and shape.
Aluminum flashing is malleable and relatively easy to shape around corners. It is most appropriate for bird and bat exclusion since raccoons and rodents can usually chew or claw through it. Caulk, sealant (for movable joints), copper gauze (such as Stuff- It®), and foam insulation can be used to seal cracks and other small openings.
Animals frequently enter structures through vents. Replace damaged and vulnerable vents with designs that are more resistant to animal entry.
- Roof vents (or louvers) should be either metal or heavy-duty plastic. The best models are totally enclosed to prevent birds and rodents from nesting inside the vent.
- Ridge line vents come with end caps that frequently work loose. This allows small animals such as sparrows, mice, and bats to easily access attics. Replacement caps (either purchased or homemade) will secure these vents.
- Ventilation openings in soffits (under eaves) are frequently used as entry sites by a wide range of animals from house sparrows to Rat wall against a building. Lomanco® 750 Ridge line vent Vent in soffit 16 raccoons. These openings are best protected by metal louvers securely attached to the soffit.
- 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 that birds cannot nest in them. Screening on the back of the vent also needs to be intact to keep bats and insects out of the attic.
- Clothes dryer vents often offer an entryway to small animals. Be careful when screening these vents because a buildup of clothes lint will damage the dryer. Screens need to be cleaned frequently or the vents can be replaced with models that are designed to exclude animals without lint clogging.
- Sewer vent pipes should be covered with commercial shields to prevent rodents and birds from entering the pipes.
Cover the Chimney
Raccoons, squirrels, bats, many birds, or any animal that dens or nests in cavities, will sometimes descend chimney flues. Entry can be prevented by the use of chimney covers. Commercially produced covers will meet the ventilation safety requirements of fire codes.
Many chimney cover designs attach to a single tile flue liner. These generally bolt to the outside of the tile liner or have legs that slip inside the flue.
Covers, that slip inside the tile liner prevent squirrel and bird access. Raccoons can usually remove these covers, and designs that bolt to the side of the flue are better if raccoons are a problem. Models with the smallest openings that meet fire codes are best for bat exclusion.
Other chimney covers attach to or around the crown (top) of the chimney. These covers are particularly helpful if there are several flues per chimney or there are no tile liners extending through the crown.
There are commercial covers designed to fit metal chimneys and these will keep out animals. If installed carefully, many metal chimney tops can also be enclosed with half-inch hardware cloth. Make sure any covering meets fire code requirements.
Several chimney cover manufacturers are able to custom fit covers for unusual chimneys. Call the manufacturer to find out what chimney measurements are needed. Custom-made covers are usually more expensive than mass-produced, standard covers.
Most chimney covers are made of stainless steel or galvanized steel. Others are made of copper or aluminum. Some designs function both as a cover and a damper.
For the Birds
A wide range of specialized products for bird exclusion have been developed, and new products and accessories come on the market frequently. Most products fall under the following categories.
- Netting is often used to deny birds access to alcoves and other spaces. Bird netting is made from a variety of materials (including polyethylene twine and extruded polypropylene) and in a range of grid sizes and strand width. Specialized hardware is also available for attaching netting to different substrates.
- Metal or plastic spikes, such as Catclaw®, Bird-B-Gone®, ECOPIC®, and Nixalite®, help prevent birds from roosting at specific locations. Metal coils (e.g., Bird Barrier®) function similarly.
- “Post-and-wire” technology uses stainless steel wires or thin cables arranged in parallel lines or grids. This method is especially effective for pigeon exclusion. Parallel 80+ pound test monofilament lines also work well although are not as durable.
- Electrified systems (as Avian Flyaway®, Flex-trak®, Bird Jolt™) are designed to shock birds without killing them and thus exclude them from specific locations. The cost of installing these systems is often high, but the systems generally have a long working life.
- Heavy plastic or rubber strips suspended in large open doorways can help prevent bird access. People and machinery are still able to move through the strips.