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[Narrator:] Sanitation is the key to permanent rat control, for it strikes at the rat's basic requirements of food and harborage.
To reinforce the effects of sanitation, rats must be cut off from entry into buildings through any actual or potential openings.
An exposed wooden edge on a door affords the rat a starting place for gnawing and eventual entry.
Starting with a one-eighth inch crack, a rat can gnaw an opening in a single night.
Wooden window frames are penetrated with the same ease.
Most foundation vents are open doors for rats.
Service wires can be runways to entrances otherwise beyond reach.
Ratproofing is the treatment of buildings to prevent rat entry or exit.
The gnawing ability of rats is remarkable.
Their cutting tools are their long, sharp incisors.
In one series of experiments, rats in search of food cut through a variety of materials.
One-eighth inch compressed fiber hardboard with a quarter-inch gnawing edge was penetrated in two nights.
Quarter-inch plywood with no gnawing edge, four nights.
Three-eighths inch plasterboard with no gnawing edge, five nights.
Three-eighths inch marine sheathing, no gnawing edge, seven nights.
Two-inch foam glass, no gnawing edge, 13 nights.
Twenty-four SO aluminum alloy almost a tenth of an inch thick, gnawing edge one-quarter inch, 11 nights.
Asbestos flexboard three-sixteenth's inch thick with an eleven-sixteenths inch hole took 51 nights.
With a simulated channel of 61 ST aluminum alloy, one-fiftieth of an inch thick with a quarter-inch gnawing edge,
it took 170 nights to penetrate one thickness.
Some materials, however, such as galvanized sheet iron, are almost completely rat-resistant.
Galvanized sheet iron and galvanized hardware cloth are the basic materials used in typical ratproofing operations.
Large centralized workshops should be equipped with a metal slither, a specially designed metal-bound work table,
templates developed for use in repetitive shop operations, and a complete set of sheet metal hand tools.
A metal-bending brake is also essential.
Employees should be skilled sheet metal workers, since each item fabricated must be custom-made.
Careful attention to field specifications is necessary, or the completed work will be useless and will have to be scrapped.
Central workshops speed ratproofing operations by providing adequate workspace
for the required equipment, much of which is large and cumbersome.
Close attention should be given to the arrangement of the equipment, so as to save time in moving materials from one to the other.
A complete array of sheet metal equipment expedites fabrication, provides consistent quality,
and gives the finished materials a uniform craftsman-like appearance which is pleasing to the user and to the public.
Fabrication instructions must be based upon efficient design.
They must specify proper materials and methods of assembly,
so as to assure adequate protection against rat gnawing over a maximum life span.
Thus, galvanized hardware cloth could be used without a metal frame,
but experience has shown that its useful life is greatly prolonged by placing it in a sturdy metal frame.
Large items can be fabricated easily in the shop, thus field personnel are freed to devote their time to installation work and to fabricating small items.
In order to expedite installation of ratproofing materials on buildings, a mobile workshop can be designed to permit simple, on-the-job fabrication
and to carry equipment necessary for installation.
It should provide work tables, a metal-bending brake, and hand tools for metalwork, woodwork, and masonry.
Also, it must have storage space for standard ratproofing materials such as galvanized sheet metal, galvanized hardware cloth,
cement, bricks, and for various sizes of lumber.
The materials used and the method of ratproofing depend on the job to be done.
This wooden door was cut through because its loose fit gave the rat a gnawing edge.
It can be ratproofed with a standard metal cuff and channel.
The threshold should be of metal or at least should be covered with sheet metal.
Clearances around the door should be three-eighths inch or less.
Treatment of the door, the threshold, and the jambs with sheet metal prevents rat entry by gnawing.
Naturally, if the door is left open, it fails to keep out the rats.
More rats enter buildings through open doors than by any other means.
If a door must be kept open for ventilation or other purposes,
the entrance should be protected by a rat-proof screen door equipped with self-closing hinges.
The lower edge of the screen door should be cuffed and channeled.
The rats cannot enter any opening if the width or height of the opening is less than one-half inch.
Hardware cloth with a half-inch mesh will keep rats out.
A quarter-inch mesh will keep mice out also.
This window should be repaired.
A ratproofing screen of a quarter or half-inch mesh hardware cloth in a sheet metal frame should be installed in front of the window.
Foundation vents should be protected by hardware cloth of a quarter or a half-inch mesh.
Holes left by the installation of service pipes should be filled immediately with a good grade of cement mortar.
Such ratproofing measures, while of the utmost importance, are relatively simply and obvious.
Others are more difficult and extensive.
For instance, this cellar is rat-infested.
How did rats get in?
They burrowed under the foundation wall and entered through the earthen floor of the cellar.
Ratproofing of cellars can be accomplished in one of two ways.
An L-shaped curtain wall of concrete can be built adjoining the foundation wall to a depth of 24 inches below the surface of the ground.
The lip of the curtain wall should be at least 12 inches wide and four inches thick.
Curtain walls are effective because of the habits of rats.
Occasionally, rats seeking an entry may burrow eight to 12 feet deep beside a foundation wall.
Usually they will not give up unless they meet a horizontal obstruction, which they take to be a floor.
Rats apparently refuse to burrow away from their objective.
L-shaped curtain walls of these dimensions have thus far baffled rats.
Another way of ratproofing a cellar is by installing a concrete floor closely joined to the foundation wall.
This is the method of choice because it excludes rats, and at the same time adds value to the building.
Rats excluded from a building by sealing off their usual routes will seek other ways of access,
thus it is necessary to make it impossible for rats to enter less-accessible points.
For example, either this tree should come down or the window should be rat-proofed.
These eaves are potential points of entry.
They are accessible from the roof and from the wires along the side of the house.
Covering the eaves with hardware cloth protects the building from rats and also from squirrels and birds.
Ventilation, the purpose of the open eaves, remains effective.
Roofs, which rats are able to reach, need special attention.
On this roof, rats are harboring at the junction of the parapet wall and the roof, and are entering the building through the soil vent pipe.
Hardware cloth protects the soil vent from rat entry.
The next step should be to eliminate the harborage at the parapet wall.
In any building, every probable point of rat entry must be located and then ratproofed.
There are many types of buildings that need ratproofing.
Each has problems peculiar to its geographical location, the type of construction, and proximity to other buildings.
But it is not only the exteriors of buildings that have to be treated.
Many establishments are so constructed that they furnish an unnecessary amount of interior structural harborage.
The double-partition wall is the most common example of structural harborage.
Within this double wall, for instance, there is a Norway rat nest.
Another double wall provides a perfect runway for roof rats.
After ratproofing is completed, rats usually are found to be still in the building.
Where a building contains sources of food and water plus adequate harborage,
the rat population inside the building will continue to thrive until further rat-control measures are taken.
The remaining rats must be killed.
Special rat-killing techniques have been devised to speed rat eradication in ratproof buildings.
These special techniques should be used immediately after ratproofing.
In urban areas, ratproofing problems usually involve adjoining buildings.
Where buildings have exterior walls almost adjoining, rats may harbor between the walls, feeding in the adjacent premises.
Or where the buildings have a common wall, the rats may harbor in one building and feed in the next.
This fact has an important bearing on ratproofing of urban property.
Here is a half of a city block with a frontage of 200 feet and a depth of 75 feet.
This half-block is divided into eight premises of equal size.
Each has a frontage of 25 feet and a depth of 75 feet.
If each premise is to be ratproofed separately, work will have to be done on a total of 1075 linear feet.
Such ratproofing is expensive, but it is necessary to ratproof each premise separately.
Study of rat habits indicates that rats live in a limited home range.
Rarely do they cross the street.
Therefore, for economy in ratproofing, the entire half-block must be considered not as individual premises but as one unit.
Ratproofing the perimeter of the whole group of adjoining premises ratproofs the entire half-block, and reduces the area to be treated to about half.
Ratproofing on a block basis is both the most efficient and most economical procedure, and complies with the island theory of rat control.
The island theory assumes that each block forms an island of rat life.
After the block has been ratproofed, the rats within each premise are eradicated.
After a block has been ratproofed and rat-free, it has to be maintained.
Damage to rat-proof installations can occur through accidents or carelessness.
Such damage may result in reinfestation.
The window must be ratproofed again and the building freed of rats.
The most efficient, the most economical, and the most lasting ratproofing results from proper design and construction of rat-proof buildings.
Rat-proof materials are used at all rat-accessible points.
Material having a maximum opening of one-half inch in the least dimension, is used at all potential points of entry that can be reached by rats.
Expanded metal, as installed here, is far superior to hardware cloth, both in strength and permanence.
Rat-proof construction eliminates most of the interior harborage found in usual construction.
There are solid basement floors and no double floors, or ceilings.
No opening is left around service pipes where they pass through walls.
There are no double walls.
There are no enclosed spaces in stairwells, nor boxed-in spaces in or under shelving.
These are but a few of the features recommended by revised building codes aimed at the rat-proof construction of buildings.
Buildings so constructed can be kept rat-free with a minimum of labor and expense.
When we learn to practice continuous anti-rat sanitation, when all our buildings have been ratproofed by techniques such as these,
followed by thorough rat eradication, then man will have gone far toward ridding himself of his unwanted and deadly companion, the rat.
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