Figure 17.—A, Broken floor drains provide a ready means for invasion by rats; B, rat tracks in freshly laid concrete around newly repaired drain show that before repairs were made the drain was a rat highway
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.])
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Figure 18.—A, Openings around pipes are a common source of rat infestation; B, situations like this give rats access to otherwise rat-proof buildings
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.