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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 are 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 NWCOs prefer to use welded wire mesh to create rat walls and for any other installation that's meant to last a long time. Recommended size for larger animals is 1 × 1" mesh, while 1/2 × 1/2" mesh is suitable for most smaller animals.
Aluminum flashing is flexible and relatively easy to shape around corners. It's 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; typical brands include Stuf-Fit™) and expanding foam insulation. These materials are great for sealing cracks and other small openings.
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.
At left: Lomanco 750 roof vent. Right, a ridgeline vent.
Roof vents (or louvers) 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. There are also commercial stainless steel box screens that are secured over existing vents.
Ridgeline vents come with end caps that frequently work loose. This allows small animals, such as sparrows, mice, and bats to easily get inside attics. Replace the caps to secure these vents.
Soffit vent seen from below
A wide range of animals, from sparrows to raccoons, often find their way into a building through the ventilation openings in soffits that are located under the eaves. Securely attach metal louvers to the soffit to protect these openings, which are also called "soffit vents."
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.
|sewer vent covered with a pipe shield|
Clothes dryer vents are another popular route 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.
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.
Raccoons, squirrels, bats, many birds, or any animal that dens or nests in a cavity (such as a hole in a tree) will sometimes go down a chimney flue. You can prevent this by installing a chimney cover on the top of the chimney. Commercial models will meet fire codes. Most chimney covers are made of stainless steel or galvanized steel, but there are copper and aluminum models. Some work both as a cover and a damper.
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 keep squirrels and birds out, but raccoons can usually remove this kind of cover. If raccoons are a problem, choose a chimney cover that bolts to the side of the flue. Choose models with the smallest openings allowed by fire codes to exclude bats.
|Left, chimney cover with damper. Model shown at right attaches to the outside of a tile liner.|
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.
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). It's available in different grid sizes and strand width, with specialized hardware to attach the netting to many kinds of materials.
Netting is often the most effective method to control bird damage. The cost varies a lot. Up-front costs may be quite high, because of the labor needed to install the netting (it must remain taut over time, which takes some doing), but it's often economical in the long term. The material tends to last three to ten years.
By converting a flat perch into a sloped one using a piece of wood or a plexiglass panel, you can deter birds from landing on ledges and ornamental architectural features.
|Spikes and coils turn ledge into uncomfortable roosts. (Bird-Flite® Spikes and Bird Coil® from Bird Barrier™.)|
Metal or plastic spikes help prevent birds from roosting on ledges, roof peaks, window sills, signs, and ornamental architectural features. "Porcupine wire" is a device with sharp stainless steel prongs sticking out in many angles (i.e., Catclaw®, Bird-B-Gone®, ECOPIC®, and Nixalite®). Metal coils, which look like a slinky, work the same way.
"Post-and-wire" grids discourage birds from landing in an area. The grid is made of stainless steel wire, thin cables, high-tech braided fishing line, or 80+-pound test monofilament lines. (Maintaining tension is essential, so steel wire is a better choice for a permanent installation because it will need less maintenance. Monofilament line stretches and can break.) The cables are stretched tightly over the vulnerable area in a square pattern, as parallel lines, or just as a single line across a narrower area, such as a ledge. Birds react differently to this exclusion technique. It works best to discourage gulls, crows, and pigeons from such areas as rooftops, ledges, landfills, courtyards, and fish hatcheries. If using metal, consider the possibility that this installation could be a lightning hazard.
|About a half-dozen cables were stretched across this wide ledge, supported by four posts. This shows the parallel line installation. On a narrow ledge, one cable might be enough.|
Electric shock devices (Avi-Away®, Flock-Shock®, Flyaway®, VRS®) deliver a nasty enough shock to be taken seriously, but they don't kill the birds. They're used to keep birds off ledges. The cost of installing these systems is often high, but the systems generally have a long working life.
Commercial plastic strips can provide bird-proof barriers for doors to warehouses, grain storage areas, and other buildings. These strips can be hung from the top of the doorframe to ground, allowing people and equipment to easily pass through the door.
Fences tend to provide the most effective exclusion. They can be made of many materials, such as woven wire, hardware cloth, electrified wire, rope, bird netting, or some combination of materials. Fences vary dramatically in design and cost. This device works on both a small scale (individual plant) and a large scale (garden, field, orchard, park). Some are permanent installations while others are temporary and portable. Permanent fences require maintenance. All fences need to be adequately secured.
The most effective fences are designed with the particular abilities of the target animal in mind. For example, does it jump or burrow? Repellents will sometimes be used in combination with a fence. A cloth dipped in repellent may be tied onto a rope fence, for example—adding oomph to a cheap and simple fence (but that does qualify as a pesticide).
Tree wrap, tree guards, and chicken wire cages, and hardware cloth can be wrapped around trees and shrubs, or draped over individual plants to protect them from being chewed or girdled. Keep the mesh about an inch away from the plant so it has some room to grow. Don't staple the material to the tree because that could lead to rot. Later on, if someone wanted to cut that tree down, the staples could prove dangerous.
|This fence design, called a rat
wall, is often attached to foundation, deck, 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 6-12 inches deep. Notice that it's bent at a 90O angle, forming the letter "L". This shelf helps to stop animals from digging under the fence. The shelf should stick out 6-12 inches.
One-way doors can be "installed" in the rat walls to release the animals. 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 finish the exclusion. (An easy way to test for animal activity is to put some nontoxic tracking powder or flour on the ground under the porch, in the animal's route. Check later for tracks.)
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