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.])
Figure 4.—A, Detail of old barn with floor supported a few inches above ground on girders and posts; B, same barn made rat proof with concrete foundation and floors and cement-plastered walls
Figure 5.—Method of rat proofing old stable, A. Concreting and plastering as shown in B makes for better sanitary conditions behind stock
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].