Every separate structure presents its individual problem, but there
are two general principles that apply in all cases and that should be
kept in mind when the rat proofing of any building is being considered.
First, the exterior of those parts of the structure accessible to
rats, including porches or other appurtenances, must be constructed
of materials resistant to the gnawing of rats, and all openings must
be either permanently closed or protected with doors, gratings, or
screens; second, the interior of the building must provide no dead spaces,
such as double walls, spaces between ceilings and floors, staircases,
and boxed-in piping, or any other places where a rat might find safe
harborage, unless they are permanently sealed with impervious materials.
All new buildings should be made rat proof. When plans are being
drawn for a building, the rat problem is frequently overlooked,
usually because rats are not often present near sites selected for
new structures. They are certain to come later, however, and should
therefore be taken into account. Modern structures are so nearly
rat proof that to make them completely so requires only slight and
inexpensive changes. Furthermore, rat proofing is closely associated
with fire stopping and with sanitary measures that are now required by
law in many places. Cities in growing numbers have added rat proofing
clauses to their building ordinances with such good effect that others
are sure to follow their lead. Builders should therefore compare the
cost of rat proofing during construction with the probable later cost,
in case local laws should require that all buildings be made rat proof.