RAT PROOFING BUILDINGS
AND PREMISES

By James Silver, Associate Biologist, and W. E. Crouch, Senior Biologist, Division of Predatory-Animal and Rodent Control, Bureau of Biological Survey, and M. C. Betts, Senior Architect, Division of Agricultural Engineering, Bureau of Public Roads.

CONTENTS

INTRODUCTION

THE PRINCIPLES of modern construction of buildings are opposed to everything conducive to the best interests of the rat. They call for the liberal use of indestructible and noncombustible materials, as well-made concrete and steel, and these are too much for even the sharpest of rodent incisors. They include, also, fire stopping in double walls and floors and the elimination of all dead spaces and dark corners, and the rat is left no place in which to hide. They embody sanitary features that provide for hygienic storage of food, and the rat can not live without something to eat.

Many men have devoted their lives to a study of methods of rat control, and as a result countless preparations, devices, and contrivances are constantly being made available. Trapping, snaring, trailing, flooding, digging, hunting, ferreting, poisoning, and fumigating are employed, and rat limes, rat lures, rat repellents, and bacterial viruses are resorted to, and even antirat laws, local. State, and national, are constantly being passed in a world-wide effort to conquer this rodent. These have been important factors in keeping down the surplus, but all destructive agencies that have been used have utterly failed to reduce materially the total number of rats in the world. Rat proofing, however, is at last making definite headway against the age-old enemy of mankind, and it is upon this that the ultimate solution of the rat problem will depend.

The destruction of rats for temporary relief and for keeping them under control in places where rat proofing is not possible or practicable will always be necessary, and knowledge of the best means of destroying rats is essential to any rat-control program. Information on poisoning, trapping, and other means of destroying rats is given in Farmers' Bulletin 1533, Rat Control. Permanent freedom from rats, however, should be the goal of everyone troubled with the pests and rat proofing offers the best means to this end.

GENERAL PRINCIPLES OF RAT PROOFING

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.

RAT PROOFING FARM BUILDINGS

The cost of rat proofing the entire premises of many American farms would amount to less than the loss occasioned by rats on the same farms during a single year. In no other place is rat proofing more badly needed or less often accomplished than on the farm. There are, however, numerous examples of rat-proof farms in nearly every county in the United States, and almost invariably they are the more prosperous farms, for the rat proofing of a farm is an indication that the farmer has learned the necessity of stopping all small leaks, which mean reduced profits.

A rat-proof farm is not necessarily one in which the entire farmstead is absolutely proofed, but rather one where conditions are so unfavorable for any invading rats that they either will desert the premises of their own accord or may be easily routed by man or dogs. The source of the trouble on almost any heavily rat-infested farm can be traced directly to conditions that furnish rats safe refuges near abundant food. The commoner of these rat-breeding places are beneath wooden floors set a few inches off the ground in poultry houses, barns, stables, granaries, corncribs, and even residences; in piles of fuel wood, lumber, and refuse; in straw, hay , and manure piles that remain undisturbed for long periods beneath concrete floors without curtain walls; and inside double walls of buildings. In rat proofing the farmstead as a whole, attention should first be paid to the premises outside the buildings and later to each building separately.

Neatness is of prime importance in keeping a place free from, rats, and providing facilities for keeping it neat should be considered part of the rat-proofing program. An incinerator, which can be made from a discarded metal drum or rolled-up poultry netting, is convenient for burning all trash and combustible waste; and a deep, covered pit with a trapdoor will take care of tin cans and other noncombustibles, if it is not practicable to haul them away at regular intervals. A covered garbage can is also indispensable on farms where table scraps are not fed directly to poultry or hogs. (Fig. 1.) Raised platforms, 18 or more inches high, should be provided upon which to pile lumber or other materials that if placed on the ground would afford shelter for rats. (Fig. 2.)

Large piles of cut stove wood on many northern farms become rat infested. The same is true of manure piles adjoining barns and, to a lesser extent, of hay and straw stacks near farm buildings. These do not provide food and are attractive to rats for harbors only if near a source of food supply; moving them to a place at some distance from where foodstuffs are handled will usually solve the problem.

Stone walls at times furnish excellent harborage for rats but, like the woodpile, only if there is ample food near by. Stone walls supporting embankments and driveways on sloping farmsteads are most frequently infested, and when this occurs the inviting openings can usually be readily closed with small stones and cement.

Ditch banks often are a source of rat infestation, but in most climates during the warmer months only. The rodents concentrate in such places because they are less likely to be disturbed there. Rat proofing the ditch bank consists merely of burning or otherwise destroying the protective vegetation. This, of course, affords only temporary relief and should not be considered strictly rat proofing.

The use of concrete in the construction of most farm buildings is usually the best means of permanently excluding the rat. Fortunately, many of the fundamentals of rat proofing are also principles of good construction. As am example, in order to support a building properly, the foundation should extend well into the ground below the frost line; rat proofing likewise requires that the foundation wall extend at least 2 feet below the surface. Rats seldom burrow deeper than 2 feet unless natural passageways assist. Foundation walls should project a foot or more above the ground in order to protect the wooden parts of the building, and this also lessens the opportunity for rats to gnaw through the wall. A rat is not likely to cling to the exposed exterior of a building a foot above the ground while it gnaws a hole through wooden sheathing or siding. It would do so very quickly, however, if such siding extended to the ground, where its work could be under cover of vegetation or behind some object, particularly when the siding becomes somewhat rotted, as would soon happen were it close to the ground.

It is important that concrete be hard, as weak concrete is but a slight obstacle to the sharp rodent incisors. The mixture approved for ordinary building construction, however, is sufficiently hard to be entirely rat proof, and it is essential that approved practices of mixing and placing concrete be followed. Directions for using concrete and for building concrete floors are given in Farmers' Bulletin 1279, Plain Concrete for Farm Use, and in Farmers' Bulletin 1480, Small Concrete Construction on the Farm. Other approved building practices, such as fire stopping double walls, eliminating waste dead spaces, making doors, windows, and ventilators fit tightly, and screening or permanently stopping all openings, are also necessary in rat proofing. For simple farm buildings the foundation illustrated in Figure 3 meets all the requirements of good construction and will keep the rats out if the walls are tight.

BARNS

Old barns with wooden floors supported a few inches above the ground on girders and posts are particularly objectionable from the standpoint of rat infestation and should be rat proofed with concrete. (Fig. 4.) A concrete foundation wall extending at least 2 feet below grade is placed under the girder between the posts. The wooden posts may be removed after the wall has hardened, and the spaces left should then be filled in with concrete. A concrete floor is laid, and cement stucco on metal lath is extended up the walls for at least 2 feet, preferably to the level of window sills.

Rock foundations in many old barns offer excellent harborage for rats unless pointed carefully with cement mortar. If possible, the floor should be raised to the level of the sill and the walls plastered to the window-sill level (fig. 5) in such manner as to prevent access by rats to spaces between the studs.

The grain bin and other similar fixtures must always be considered in rat proofing a barn. It is most important that they be so situated or constructed that there shall be no hiding places for rats behind or under them. The grain bin should be completely lined or covered with metal and should have metal-clad lids. Any open spaces behind or under the bins should be tightly closed with metal. (Fig. 6.)

Other accessories of various kinds of barns should be examined carefully and remodeled or moved if necessary to exclude rats or eliminate harbors. The haymow frequently presents a difficult problem in a heavily infested barn, but the haymow alone is seldom responsible for the rats, for if all other rat harbors in the barn are effectively eliminated or shut off, the rats will not long remain with the hay as their only shelter. If the lower walls are of rough surface or composed of open studs covered on the outside, rats can climb at the corners. They may be prevented from doing so by the application of a strip of metal 8 inches wide placed just below the joists of the upper floor. Recommended construction of walls and floors in new frame barns is shown in Figure 7.

CORNCRIBS

Another method, and one that is less expensive and quite effective as long as kept in good repair, is shown in Figure 8. Wire netting should be carried around the entire crib to a height of 2 feet or more from the top of the foundation. A strip of galvanized iron 8 inches wide should be fastened above the wire netting. The joints between the foundation and netting and between the netting and metal strip must be tight. As rats are unable to gain a footing on the smooth metal and can not climb over it, it is unnecessary to use wire netting above the strip. Care should be taken to join the lengths of metal tightly and to carry the wire netting and strips of metal across and around both sides of doors and door jambs. It is also advisable to provide doors with springs or weights to insure their remaining closed.

If possible the corncrib should have a concrete foundation and floor, as illustrated. Otherwise it should be elevated on posts or piers so that it will have a clearance underneath of feet or more. If the supporting posts or piers are covered with sheet metal, or are protected at the top with metal collars or disks extending at least 9 inches out from the posts, rats will be kept out of the crib. Old cribs can often be rat proofed in this manner at little expense. Dish pans and washtubs make convenient rat guards. (Fig. 9.) It is important that the area beneath the corncrib be kept clear and that nothing that the rats can climb be leaned against it.[1]

GRANARIES

The rat proofing of granaries is of great importance, because of the abundance of food stored there and the corresponding opportunity for serious loss. The granary with concrete foundation and floors, tight-fitting doors, and screened ventilators presents no unusual problem, except possibly in connection with the elevator pit, which should be carefully checked against possible means of ingress for rats. Small wooden and portable granaries should be protected with wire netting. (Fig. 10.)

Concrete feeding floors, troughs (fig. 11), water tanks, hog wallows, and similar structures should be constructed with a curtain wall, or apron, around the outer edge extending 2 feet or more into the ground (fig. 12) to keep the rats from burrowing underneath the slab. This also tends to prevent the heaving caused by frost and the uneven settling of the structure in soft ground.

POULTRY HOUSES

It is not practicable to attempt to exclude rats from poultry houses, but such buildings can easily be made proof against serious trouble by the elimination of all places where the rodents can obtain safe harborage. Most rat infestation around poultry plants is due to the presence of numerous shelters and suitable breeding places. Three things are particularly to be avoided: Wooden floors on or within a few inches of the ground; double walls; and nest boxes, feed hoppers, and other fixtures placed so as to provide shelter for rats under or behind them. From a rat-proofing standpoint the floors as well as the foundation should be made of concrete. (Fig. 13.) If this is not considered practicable, wooden floors should be elevated so as to insure a clear space of 2 or more feet between the floor and the ground. Warmth can be provided, if necessary, by two thicknesses of flooring with tar paper between. Hollow walls almost invariably furnish harborage for rats. The inner stud covering therefore, should be torn out, but if warmth is a factor to be considered, siding should be put over sheathing on the outside of the studs with building paper between.[2]

The premises around the poultry house should be cleared of all rat harbors by elevating all objects under which a rat can find shelter. (Fig. 14.) Near-by buildings particularly should be considered, for it is frequently found that rats living exclusively on poultry feed occupy harbors 50 or more feet away from the food source. For this, reason it is desirable to build poultry plants at least 100 feet from any possible rat harborage. The vast number of young chicks killed annually by rats would be greatly reduced if these simple precautions were taken.

OTHER FARM STRUCTURES

Outside cellars frequently become infested with rats, and great havoc to stored produce almost invariably results. Considerable expense, if necessary, is justified in making the storage cellar rat proof. A cellarway with wooden steps and sills and earth floor is usually the source of the trouble. The sill soon rots or the rats burrow under it to gain entrance. The remedy is to construct a concrete floor and cellarway. This not only will exclude rats but will prove more economical in the long run. (Fig. 15.)

RAT PROOFING CITY BUILDINGS

In rat proofing a city building it is well first to look to the exterior. If the locality is heavily infested with rats, some are almost certain sooner or later to find their way into the building however well protected against them it may be. Garbage and trash usually comprise the bulk of the rats' food supply. A metal, water-tight garbage can, large enough to contain all garbage accumulations between collections and having a close-fitting lid (fig 1), is of prime importance and should be required in all cases by city law.

Large accumulations of trash usually, contain much waste food (fig. 16) and are certain to attract rats and furnish an ideal breeding place for them. Furthermore, they are a menace to health and should not be tolerated under any circumstances. All other rat harbors, such as wooden floors and sidewalks very near the ground, should be removed or replaced with concrete, and piles of lumber and various materials stored out of doors should be removed or elevated 18 or more inches. Particular care should be taken to see that sheds and other outbuildings, porches, steps, loading platforms, and similar structures on the premises are made rat proof, either by the use of concrete, by elevation, or by keeping them open to the light and easily accessible.

A thorough inspection should next be made of the building itself and careful note taken of alterations and repairs necessary for a thorough job of rat proofing. Inspection should begin in the basement. Doors and windows should fit snugly, particularly doors leading to outside stairs or elevators, and these should also be provided with automatic closing devices. Windows and ventilators should be screened or covered with gratings, the openings not more than half an inch square. Defects in basement floors should be repaired with concrete, and floor drains should be fitted with tight covers, (Fig. 17.)

Side walls should be carefully inspected, and all openings made for plumbing (fig. 18), electric-wire conduits, areas around windows and doors, and unpointed joints in masonry walls (frequently left when the exterior of the wall is hidden from public view by porches or platforms) should be carefully closed with cement mortar. (Fig. 19.)

Basement ceilings, when accessible to rats, cause much trouble, and frequently the best remedy is to remove them entirely. In frame construction spaces between studs in walls opening into basements also are a common cause of rat infestation of the whole building. The permanent closing of these spaces with noncombustible material not only shuts out the rats but also reduces the fire hazard by stopping the drafts and the rising of heated gases should a fire start in the basement. This process of blocking spaces between studs and furring is commonly known as fire stopping and is of such importance that the building regulations of many cities now require it. Figure 20 illustrates practical methods of rat proofing stud spaces in old buildings.

In the Southern States, where the roof rat occurs, similar care must be taken to make the upper floors and roofs of buildings rat proof, as this rat is an expert climber and frequently enters buildings by way of the roof. Doors at the top of stairs and elevators should fit snugly, and all ventilators, exhaust fans, unused chimney flues, and other openings should be screened. Broken skylights and openings under eaves and places where electric wires enter the building should be repaired or closed.

Buildings that have neither basements nor continuous masonry foundations present more difficult rat-proofing problems. The most effective procedure is to construct a concrete foundation wall between the existing supports and, after the wall has hardened, remove the supports, if of wood, and replace them with concrete to make the wall continuous. Where the cost prohibits following this plan and where the supporting sill and joists are at least 2 feet above the ground level, satisfactory rat proofing may be attained by stopping the spaces between the studs with weak concrete or other material resistant to rats for a distance of 8 inches above the floor level, or with galvanized-metal flashing nailed to the joists, plate, and floor. (Fig. 21.) The space beneath the building must be free from all rubbish and other material that would afford shelter for rats. A continuous masonry foundation, with screened openings to provide ventilation, presents a more pleasing appearance.

If the clearance between the ground level and the bottom of girders and joists is less than 2 feet, it may provide a hazardous rat harbor. One of three things should be done: The building should be elevated on piers 2 feet above the ground; a concrete foundation should be built as described above; or a continuous concrete curtain wall should be constructed under the entire outer wall of the building. (Fig. 22.)

Most new city buildings are now built practically rat proof, or could be made so with only minor changes in the plans and at small cost. Yet if certain essential details are not included at the start, endless rat troubles are likely to ensue. It is therefore highly desirable that plans for every new building include specifications for rat proofing.

All new buildings in which foodstuffs are to be handled should have ground floors of concrete or other rat-proof material and concrete or masonry walls extending at least 2 feet below and 1 foot above the ground surface. All unnecessary openings in the foundation, walls, and floors should be permanently closed, and windows and ventilators should be screened. Stud spaces in frame construction should be stopped with noncombustible material resistant to rats. New buildings in which foodstuffs are not to be handled may, if desired, be elevated on piers or posts to provide a clearance of 2 feet between the ground level and the bottom of the supporting girders, although the concrete or masonry wall is more satisfactory.

MARKETS

Public, farmers', and wholesale markets, commission houses, and similar places where vast quantities of foodstuffs are assembled and redistributed are nearly always infested with large numbers of rats. Such structures are usually concentrated in districts, and these often become rat-breeding centers, from which the rats constantly overflow to adjoining sections of the city. Rat proofing a district of this kind would seem to be almost hopeless, yet it has often been demonstrated that the task is not only feasible but entirely practicable. . Here, more than anywhere else, the great need is the elimination of rat shelters, which in turn means the free use of concrete or other masonry. Scrupulous cleanliness is essential in markets, but even where this is practiced it is not possible completely to eliminate rat food, so the main reliance must be placed on the removal of all rat harbors. Not only must the building in which the market is housed be rat proofed, but also all the fixtures. In old public markets the stalls were frequently constructed as if designed for the protection of rats. Dark, out-of-the-way holes under counters, stands, and shelves afford convenient places for the accumulation of trash, which it would be well to destroy; and in such locations, with abundance of food at hand, rats are in the best possible position to thrive and multiply. The use of smooth concrete or tile counters (fig. 23) erected on concrete floors deprive rats of the essential shelter, provided that the space underneath the counter is kept clean and that stored material is moved frequently. The smooth surface also prevents the rats from climbing and makes it possible to leave edible products on the counter overnight without fear of their being damaged or contaminated by the rodents. If wooden floors are used, the boards should be laid flat on the concrete or on sleepers not more than half an inch high.