Unlike rodents, bats will not gnaw their way through wood or building materials. Soft materials such as insulation batting can be easily attached to a building with a heavy duty staple gun.
Effective materials to exclude bats are expansion foam caulking, flashing, screening, and insulation. Weatherstripping, stainless steel wool, or stainless steel rustproof scouring pads are excellent materials to block long, narrow cracks.
Cracks and crevices develop in a structure as it ages and bats will take advantage of these openings. Caulking will seal the openings.
Since wood expands and contracts with the weather, it is best to apply the caulking during dry periods when the cracks will be their widest. Occasionally cracks enlarge and a filler is necessary before a caulking compound is applied. Oakum is a tarred-hemp fiber commonly used to caulk ships. It packs easily and firmly by hand into small cracks. The tar or creosote binds the fiber so that it is not easily dislodged. In addition to oakum, other fillers are caulking, cotton, sponge, rubber, glass fiber, and quick-setting putty.
There are various caulks which may be applied with a caulking gun. Latex, butyl, and acrylic have a durability of about 5 years and can be painted. Elastomeric types, such as silicone rubber and polysulphide rubber, will last indefinitely, expand and contract with the weather, do not dry or crack, tolerate temperature extremes, and come in colors. However, some cannot be painted. Silicone rubber is clear, long lasting (10-year guarantee), and almost invisible, thus matching any decor.
Self-expanding urethane foams for caulking have appeared in pressurized containers and are dispensed similarly to shaving cream. Though quite messy and difficult to clean, when the material is placed in a hole it will expand several times to fill the space. After it cures and hardens, it may be trimmed, sanded, and painted with any type of paint or stain. Spray foam will weather, limiting it's use to very deep crevices and interiors.
Houses may need to be caulked in the following places:
- Between window drip caps (tops of windows) and siding
- Between door drip caps and siding
- At joints between window frames and siding
- At joints between door frames and siding
- Between window sills and siding
- At corners formed by siding
- At sills where wood structure meets the foundation
- Outside water faucets, or other special breaks in the outside house surface
- Where pipes and wires penetrate the ceiling below an unheated attic
- Between porches and the main body of the house
- Where chimney or masonry meets siding
- Where storm windows meet the window frame
- Where the wall meets the eve at the gable ends the attic
- Where wall meet the eves anywhere on the structure.
When bats crawl under doors, the space between the floor and the door bottom may be sealed with weatherstripping, a draft shield, or a gap stopper to close off the space between the bottom of the door and the door sill or threshold. Weatherstripping is made of a variety of materials including natural fibers, aluminum, fine wire, felt, hard rubber, vinyl, and nylon. A nylon strip brush barrier is set in a galvanized steel channel and housed in either aluminum or vinyl. It has several advantages over ordinary weatherstripping. The flexible nylon filaments, which comprise a substantial brush, move easily in any direction permitting the bristles to conform to uneven floor surfaces, including carpet. This seals any gaps, stops drafts, and reduces heat loss. It is said to resist rodents and insects.
A simple draft excluder for the bottom of seldom-used doors is a long, flexible, sausage-shaped cloth tube filled with sand, which is simply pushed against the crack at the bottom of the door.
Wherever joints occur in a building, e.g., walls meeting the roof or a chimney, flashing may be installed to keep the building watertight. Flashing consists of strips of metal or other material to cover cracks, crevices, and holes. The materials most commonly used are galvanized metal, copper, aluminum, and stainless steel. A self-adhesive flashing, called "Flashband," was developed in 1965 and has been used to batproof buildings in England and western Europe for years. Flashband has advantages such as flexibility, self-adhesiveness, and a grip that reportedly improves with time despite extremes of weather. It is available in the United States and Canada.
Where screening is necessary the mesh must be small enough to prevent the access of bats. Steel hardware cloth should have 0.63 cm (1/4 in.) mesh with three meshes or more to the inch. Insect screening for windows should be 18 x 14 mesh.
Bats can enter ventilators that are not properly screened. Hardware cloth for ventilators should be 8 x 8 mesh. Inlet and outlet ventilators should be properly installed. The type of ventilator used, its location in the building, and the direction of prevailing air currents may be important factors because buildings of identical design, but different orientation, vary in their attractiveness to bats. Many ventilators are made with metal louvers and frames, others are custom made of wood to more closely fit the house design.
The soffit (the underside of an overhanging cornice) usually has ventilators which may be continuous, round, single-framed, or the soffit itself may be of perforated hardboard. Regardless of soffit type, the slots should not exceed 0.63 x 2.5 cm (1/4 x 1 inch).
Bats may use an unused or old chimney because the rough surfaces of chimney walls offer suitable places for bats to hang. Bats will almost never use an active chimney. To prevent bats from entering chimneys, spark arresters or bird screens should be installed. These should be of rust-resistant material and carefully attached. They should completely enclose the flue discharge area and be securely fastened to the top of the chimney. Except when in use, dampers should be closed.
Screening is also used as a filler for very large crevices. Strips of fiberglass screening is pushed into holes then finished off with a coating of sealant.