How to Survey and Seal Off Rodent Entry Points Into a Building

In early autumn, rats look for indoor harborage.
In early autumn, rats look for indoor harborage. (Image: Anup Shah/Photodisc/Getty Images)

Rodents such as mice and rats are most likely to enter a building as the weather turns colder and frost starts. Their outdoor habitats may not protect them from the weather, and their food source runs low as well. They are attracted to the heat within a building and potential replacement food sources. You can prevent rodents from getting inside your home and outbuildings by conducting a survey and repairing building entry points.

Things You'll Need

  • Flashlight
  • Weatherstripping
  • Cement
  • Brass wool, medium or fine grade
  • Diamond lath
  • Plastic wood putty
  • Exterior caulk
  • Probing stick, at least 2 feet long

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Think like a rodent. They circle the perimeter of your building trying to locate entry points, and you must do the same thing. Look for gnaw marks or debris that looks dug up and kicked out of an area. Point a flashlight at dark areas to inspect them.

Locate entryways for pipes or cables, even if these are a few feet off the ground. Stuff smaller openings with brass wool, which doesn’t rust. Cover the brass wool with plastic wood putty, cement or exterior caulk.

Look closely along the bottom of entry doors, including a basement door if you have one. If you can slide a pencil under the door, that allows enough room for mice to slip through; a larger gap may admit rats. If their heads fit under, the rest of their body follows. Install a heavy-duty rubber weatherstrip or build up the height of the threshold.

Seal holes or cracks near the foundation perimeter, where it meets the cement, with broken-up glass, brass wool or diamond lath mixed with cement. A rat can chew through regular cement, so the added materials serve as a deterrent.

Follow holes in the earth near the foundation, which typically indicate a rat tunnel, to the final entry point by going inside, to the basement for instance. Locate the interior entry point into the building and seal it.

Check around lower window frames for any openings, as a rodent can scale up certain porous surfaces, such as rough brick, or climb a cable wire to gain height. Seal off with wood putty, brass wool or caulk.

Check the garage door for a tight seal to the ground when closed. Address spaces at the outer edges or corners of the door, in the perimeter of the garage, at the entry door to the home and openings for wires or pipes traveling through the common wall of the garage and home.


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