Figure 21.—A, Typical construction of frame building on wooden girders and posts with Joists more than 2 feet above ground; B, sheet metal placed as shown serves to prevent the rats from climbing to a point where they can gnaw through the wood
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.
Figure 22.—A, Concrete curtain, or area wall, designed for rat-proofing purposes; it does not support the building. B, Plan of wall where supports are of wood; the concrete is bound to the posts with wire mesh. C, Plan of masonry support; concrete will adhere to the masonry if the surface is roughened
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.
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.