Environmental Health
Rodents, Bats, Insects & Other Vectors
  Rodent Prevention  

Photo of a ratWild mice and rats are unwelcome visitors to our homes. They can spread disease, destroy things in our homes, and start fires by chewing electric wires. The first strategy to avoid problems, including hantavirus (see below), is to keep rodents out of your home, well-house, sheds, and workplace. Mice can fit into holes or cracks as small as ¼ inch. Rats can gnaw through wood.

Keep Rodents Away

Seal Openings

Seal openings larger than one quarter of an inch using rodent-resistant materials such as ¼ inch hardware cloth (wire mesh), concrete, sheet metal, brick, or mortar.

  • Regularly check for cracks or openings around the foundation, attic, vents, and places where pipes or cables enter the building. Add a sheet metal collar around pipes to seal off the space between the pipe and the wall. The brochure “Rats, Let’s Get Rid of Them[PDF] includes helpful diagrams on page two.
  • Keep the space under doors less than ¼ of an inch. This will also help energy conservation. Cover the edges of doors with metal to prevent gnawing.

Discourage rodents by removing food sources, nesting and hiding places.

Rodents need food, water, and nesting sites in order to thrive and reproduce. Killing rats and mice without also reducing food and nesting sources does not work for long. Rats do not like to travel far, typically nesting, traveling, and feeding within a 250 foot radius. Focus efforts within 250 feet of your home or other area of concern.

  • Keep food, including pet food and bird seed, in rodent-proof containers. Either do not feed pets outdoors or remove food dishes promptly after feeding. Clean up spilled bird seed. If rodents are a problem, stop feeding the birds.
  • Keep garbage cans covered tightly and empty regularly. Line compost bins with ¼ inch hardware cloth.
  • Cover or remove fiberglass insulation from areas accessible to rodents. From a mouse or rat’s perspective, insulation is a perfect nesting area.
  • Avoid stacking firewood or other materials against the outside walls of living spaces and well-houses.
  • Keep shrubs and other vegetation two or three feet away from building walls and roofs. Tree branches should be six feet away from roofs, eaves, attic vents, and utility wires. Rats are good climbers.
  • Add a strip of heavy, rough gravel two feet wide and six inches deep next to building foundations and walls. Rats also burrow.
  • Keep lawns mowed, and keep ivy, brush, and other dense vegetation away from buildings to reduce hiding places for burrows and food sources such as seeds and berries.
  • While dense planting is helpful for reducing weeds and conserving water, it may not be a good choice close to the house or in areas with rat problems. In these situations choose landscaping plants with open shapes that allow space and light between plants and between plants and the ground.

Trap mice or rats with snap-traps.

Traps should be placed along walls that the rodents are known to regularly travel. Roof rats may need to be trapped along rafters. Place several traps in a row with the triggers toward the wall, or two traps with their long ends against the wall and triggers each outward from one another. This makes it more likely to catch the mouse or rat even if they jump. Check and empty traps daily and add fresh bait as needed. If there is no activity after three or four days, move the traps.

Finally, work with neighbors and other community members. While mice can be a single household problem, rats are community problems. It may take a community effort to effectively reduce food and nesting sites for rats.


Hantaviruses are a group of viruses that are carried by rodents. One of these, hantavirus pulmonary syndrome (HPS), although rare, can be extremely serious. Humans can contract the disease when they come into contact with infected rodents or their urine and droppings. Rodent control in and around the home remains the primary strategy for preventing hantavirus infection.

Additional Information

  • Hantavirus, WA State Department of Health fact sheet
  • Rodent Control and Hantavirus [PDF] - Dr. Yu article on cleanup of rat- or mouse-infested areas
  • I Smell a Rat: Solving Indoor Rodent Problems [PDF], Washington Toxics Control
  • Pest Control [PDF], WA Dept of Health, Drinking Water Program. Geared toward keeping rodents, bats, birds and other pests out of well houses and other drinking water structures, but good information for anyone wanting to keep these pests out of homes, sheds, etc.
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Popular Pages & Links
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This page last updated: 04/29/17