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House Bat Management


Location of Openings

Sources of air leakage may also provide access to bats. In very old frame houses with clapboard sidings, one should look for openings under overhangs where wood may have warped, shrunk, or decayed, leaving small, frequently obscure, spaces and holes suitable for bat entrances. Other bat accesses and heat loss openings are loose vents, cracks under loose flashing, eaves, cornices, louvers, where roof joins building, under corrugated roofing, spaces under doors and around windows, and openings where electrical wiring, outlet boxes, and water pipes enter the house (Fig. 5).

GIF -- Illustration of three locations of bat entry: eaves, roof ridge, and shingles.
Fig. 5.  Bats enter under eaves, at badly fitting ridge, and under shingles, slates, tiles. (By J. Newel Lewis, Dip. Arch., F.R.I.B.A.—Trinidad and Tobago)

Fans -- "Blower Door"

Because bats can crawl through narrow slits and apertures, these inconspicuous openings must be located and sealed for effective bat exclusion. Such holes may be located exactly by techniques used in airflow and conservation of energy studies to find where heat loss occurs in houses. D.T. Harrje and G.S. Dutt (personal communication; National Geographic Society 1981:48-49) briefly described the Princeton University's "House Doctor" methods for locating obscure holes in buildings where heat leaks occur. A house doctor is a trained specialist who, by means of instrumentation, diagnoses the heat losses in a house and provides methods to partially reduce these losses. House doctors usually work as a team of two and actually perform a partial retrofit of the house before leaving. Unlike energy auditors, who only make recommendations to save energy, house doctors require instrumentation to detect unusual and obscure heat losses. The instrumentation usually includes a "blower door" which is a door with a powerful fan mounted in it. This door may be attached to the front or back door frames of a house (Fig. 6). The fan can be set to create an overpressure (or underpressure) within the house relative to the outside.

JPG -- Photo of blower door.
Fig. 6.  Blower door from Princeton University house doctor approach. (Photo by David T. Harrje)

These fans exaggerate the airflow through all openings in the house so that air leaks can be detected by an extremely sensitive infrared scanner or by various "smoke" producing devices. To improve effectiveness, obvious outlets such as doors, windows, dampers, and ventilators should be closed. Fireplaces may need to be sealed with polyethylene sheets and tape to prevent excessive air leakage. The access door or trapdoor between the living space and the attic should be open. In house bat management, the search for obscure holes will be primarily in the attic; therefore, the access door or trapdoor should be kept closed and an ordinary 50-cm (20-inch) house ventilating fan should be attached to an attic window or ventilator (if one exists).

Simple, but ingenious, homemade devices will locate the general direction of air leaks in a house. One consists of a piece of very thin bathroom tissue or extremely thin plastic film (such as used in grocery stores to wrap meat and carry produce or the type of film used by cleaners for garment bags) attached to a clothes hanger by two clothespins or tape (Anonymous 1980a; Rothchild 1980). The tissue and film are sensitive to small air movements, so when the gadget is placed in front of a wall outlet or window frame, a flutter in the materials indicates that air is causing the movement (Fig. 7). Another method used to test windows and doors for airtightness is to move a lighted candle around the frames and sashes. Any air movement will cause the flame to dance indicating that caulking and/ or weatherstripping is needed.

GIF -- Illustration of man using clothes hanger film-tissue air leak detector in attic.
Fig. 7.  Clothes hanger film-tissue air leak detector. (Courtesy of Exxon Company, USA)

The effectiveness of the weatherstripping may be simply tested by lighting a stick of incense or a cigarette and moving it close to a window on a cold windy day. The path of the curling smoke will pinpoint the source of any air leak (Anonymous 1980a).

Smoke Generators and Air Flow Indicators

For ordinary house bat work costly infrared scanners will not be necessary. Specific air leaks can be easily found by the use of an inexpensive air flow indicator, air tester, smoke generator, or smoke stick. One air flow indicator consists of a rubber bulb and a glass airflow tube (Fig. 8). The tube contains a porous substance impregnated with a small quantity of fuming sulphuric acid. The tips of the tube are broken off and one end of the tube is inserted into the mouth of the rubber bulb. When the bulb is squeezed air is forced through the tube causing a small amount of white smoke to emerge from the tube. Faint air currents will become visible by the smoke and reveal their source (Fig. 9). The airflow tube can be used repeatedly until the smoke is exhausted. If a test is interrupted the tube can be sealed at each end with rubber caps and stored until used again. No mask is required but as the smoke contains aerosol acidic properties, care should be taken not to inhale the fumes. Since no heat is liberated during smoke generation, there is no fire hazard. This airflow indicator kit may be obtained from the Bendix Corporation, Environmental and Process Instruments Division, Largo, Florida 33540.

GIF -- Photo of air flow indicator kit.
Fig. 8.  Bendix/GASTEC Air Flow Indicator Kit. (Photo courtesy of The Bendix Corporation, Environmental & Process Instruments Division)

JPG -- Photo of air flow indicator in use.
Fig. 9.  Smoke from the Bendix/GASTEC Air Flow Indicator makes it possible to visually determine the directional pattern of air currents. (Photo courtesy of The Bendix Corporation, Environmental & Process Instruments Division)

Another type of smoke stick utilizes titanium tetrachloride which combines with air to form a nontoxic, dense, persistent white smoke. The end of the smoke stick has a cotton swab, which when crushed, produces a stream of smoke, about twice the amount as from a burning cigarette, for about 10 min. Invisible air currents then will become visible by the smoke and traced to their source. By taping a smoke stick to a pole it is possible to locate air currents in difficult to reach parts of the attic. Smoke sticks of this type may be obtained from the manufacturer, E. Vernon Hill, Inc., P. O. Box 14248, San Francisco, California 94114.

The density of the smoke generated depends on the humidity present in the atmosphere and increases with increased humidity. Thus smoke generated in completely dry air will not be visible, nor will the smoke function well if the temperature within the test area is the same as outside the house. To remedy this, the use of the blower door would eliminate the dependence on natural ventilation (D. T. Harrje, personal communication).

Obscure openings may also be located from outside the house by means of smoke candles or smoke bombs which, when ignited, produce dense white or colored smoke. Depending on size, these smoke generators will burn from 30 s to 5 min. One or more are ignited and placed inside a metal container, such as a drum or trash basket, which can be covered. Holes around the upper part of the receptacle permit the smoke to escape and mix with the indoor air. After the smoke has filled a portion of the house, its interior is pressurized with a blower door or high-flow ventilating fan. This forces the smoke out of the house and points of air leakage may be seen from the outside and marked with chalk. Smoke leakage also may be observed indoors when smoke emerges through openings in the floor, ceiling, attic, and basement.

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