First in importance, as a measure of rat repression, is the exclusion of
the animals from places where they find food and safe retreats for
rearing their young.
The best way to keep rats from buildings, whether in city or in country,
is to use cement in construction. As the advantages of this material are
coming to be generally understood, its use is rapidly extending to all
kinds of buildings. The processes of mixing and laying this material
require little skill or special knowledge, and workmen of ordinary
intelligence can successfully follow the plain directions contained in
handbooks of cement construction.[5]
Many modern public buildings are so constructed that rats can find no
lodgment in the walls or foundations, and yet in a few years, through
negligence, such buildings often become infested with the pests.
Sometimes drain pipes are left uncovered for hours at a time. Often
outer doors, especially those opening on alleys, are left ajar. A common
mistake is failure to screen basement windows which must be opened for
ventilation. However the intruders are admitted, when once inside they
intrench themselves behind furniture or stores, and are difficult to
dislodge. The addition of inner doors to vestibules is an important
precaution against rats. The lower edge of outer doors to public
buildings, especially markets, should be reinforced with light metal
plates to prevent the animals from gnawing through. Any opening left
around water, steam, or gas pipes, where they go through walls, should
be closed carefully with concrete to the full depth of the wall.
=Dwellings.=--In constructing dwelling houses the additional cost of
making the foundations rat-proof is slight compared with the advantages.
The cellar walls should have concrete footings, and the walls themselves
should be laid in cement mortar. The cellar floor should be of medium
rather than lean concrete. Even old cellars may be made rat-proof at
comparatively small expense. Rat holes may be permanently closed with a
mixture of cement, sand, and broken glass, or sharp bits of crockery or
stone.
On a foundation like the one described above, the walls of a wooden
dwelling also may be made rat-proof. The space between the sheathing and
lath, to the height of about a foot, should be filled with concrete.
Rats can not then gain access to the walls, and can enter the dwelling
only through doors or windows. Screening all basement and cellar windows
with wire netting is a most necessary precaution.
=Old buildings in cities.=--Aside from old dwellings, the chief refuges
for rats in cities are sewers, wharves, stables, and outbuildings.
Modern sewers are used by the animals merely as highways and not as
abodes, but old-fashioned brick sewers often afford nesting crannies.
[Illustration: FIG. 2.--Rat-proofing a frame dwelling by concrete side
wall (United States Public Health Service, New Orleans, La., 1914).]
Wharves, stables, and outbuildings in cities should be so built as to
exclude rats. Cement is the chief means to this end. Old tumble-down
buildings and wharves should not be tolerated in any city. (See fig. 2.)
In both city and country, wooden floors of sidewalks, areas, and porches
are commonly laid upon timbers resting on the ground. Under such floors
rats have a safe retreat from nearly all enemies. The conditions can be
remedied in towns by municipal action requiring that these floors be
replaced by others made of cement. Areas or walks made of brick are
often undermined by rats and may become as objectionable as those of
wood. Wooden floors of porches should always be well above the ground.
=Farm buildings.=--Granaries, corncribs, and poultry houses may be made
rat-proof by a liberal use of cement in the foundations and floors; or
the floors may be of wood resting upon concrete. Objection has been
urged against concrete floors for horses, cattle, and poultry, because
the material is too good a conductor of heat, and the health of the
animals suffers from contact with these floors. In poultry houses, dry
soil or sand may be used as a covering for the cement floor, and in
stables a wooden floor resting on concrete is just as satisfactory so
far as the exclusion of rats is concerned.
The common practice of setting corncribs on posts with inverted pans at
the top often fails to exclude rats, because the posts are not high
enough to place the lower cracks of the structure beyond reach of the
animals. As rats are excellent jumpers, the posts should be tall enough
to prevent the animals from obtaining a foothold at any place within 3
feet of the ground. A crib built in this way, however, is not very
satisfactory.
For a rat-proof crib a well-drained site should be chosen. The outer
walls, laid in cement, should be sunk about 20 inches into the ground.
The space within the walls should be grouted thoroughly with cement and
broken stone and finished with rich concrete for a floor. Upon this the
structure may be built. Even the walls of the crib may be of concrete.
Corn will not mold in contact with them, provided there is good
ventilation and the roof is water-tight.
However, there are cheaper ways of excluding rats from either new or old
corncribs. Rats, mice, and sparrows may be kept out effectually by the
use of either an inner or an outer covering of galvanized-wire netting
of half-inch mesh and heavy enough to resist the teeth of the rats. The
netting in common use in screening cellar windows is suitable for
covering or lining cribs. As rats can climb the netting, the entire
structure must be screened, or, if sparrows are not to be excluded, the
wire netting may be carried up about 3 feet from the ground, and above
this a belt of sheet metal about a foot in width may be tacked to the
outside of the building.
Complete working drawings for the practical rat-proof corncrib shown in
figures 3 and 4 may be obtained from the Office of Public Roads and
Rural Engineering of the department.
=Buildings for storing foodstuffs.=--Whenever possible, stores of food
for man or beast should be placed only in buildings of rat-proof
construction, guarded against rodents by having all windows near the
ground and all other possible means of entrance screened with netting
made of No. 18 or No. 20 wire and of 1/4-inch mesh. Entrance doors
should fit closely, should have the lower edges protected by wide strips
of metal, and should have springs attached, to insure that they shall
not be left open. Before being used for housing stores, the building
should be inspected as to the manner in which water, steam, or gas
pipes go through the walls, and any openings found around such pipes
should be closed with concrete.
[Illustration: FIG. 3.--Perspective of rat-proof corncrib, showing
concrete foundation by dotted lines; also belt of metal.]
If rat-proof buildings are not available, it is possible, by the use of
concrete in basements and the other precautions just mentioned, to make
an ordinary building practically safe for food storage.
When it is necessary to erect temporary wooden structures to hold
forage, grain, or food supplies for army camps, the floors of such
buildings should not be in contact with the ground, but elevated, the
sills having a foot or more of clear space below them. Smooth posts
rising 2 or 3 feet above the ground may be used for foundations, and the
floor itself may be protected below by wire netting or sheet metal at
all places where rats could gain a foothold. Care should be taken to
have the floors as tight as possible, for it is chiefly scattered grain
and fragments of food about a camp that attract rats.
=Rat-proofing by elevation.=--The United States Public Health Service
reports that in its campaigns against bubonic plague in San Francisco
(1907) and New Orleans (1914) many plague rats were found under the
floors of wooden houses resting on the ground. These buildings were made
rat-proof by elevation, and no case of either human or rodent plague
occurred in any house after the change. Placing them on smooth posts 18
inches above the ground, with the space beneath the floor entirely open,
left no hiding place for rats.
This plan is adapted to small dwellings throughout the South, and to
small summer homes, temporary structures, and small farm buildings
everywhere. Wherever rats might obtain a foothold on the top of the post
they may be prevented from gnawing the adjacent wood by tacking metal
plates or pieces of wire netting to floor or sill.