Rodent Prevention

Preventative Approach:

Rodent control is effectively accomplished by comprehensive rodent proofing, proper trapping and environmental management. Look for signs of rodent activity. The district can assist homeowners in understanding:

• Signs of Rodent Activity: How to identify possible infestations.
• Common Rodent Entry & Harborage Locations: Where to look for rodent activity.
• Basic Rodent Proofing Measures: Simple repairs and/or procedures residents can follow to prevent infestations.
• Environmental Management: Best practices for vegetation, waste, and general yard maintenance that can prevent rodent infestations.

Signs of Rodent Activity

Evidence:	Photo:
Rub and grease marks: Rats will often use the same route of travel, commonly referred to as runways.
Droppings: Rats can often be easily identified by their droppings.
Gnawing damage: Rats gnaw to keep their teeth short, they also gnaw to create entrances.
Tracks: The figure to the right shows the track marks of rats (which differ on the front and back paw), and mouse tracks (which are much smaller) and have roughly the same front and back paw print.
Burrows or holes : Rats create burrows or holes for nesting and storage.

Other common rodent indicators:

• Dead or live rodents
• Rodent odors
• Rodent sounds

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Common Rodent Entry & Harborage Locations:

• Chimney sparks and arrester
• Metal flashing around roof vents
• Tree limbs near roof
• Cables entering vents and louvers
• Gaps under megal flashing
• Gaps around chimney
• Open vents
• Openings in roof tiles
• Missing meter box cover(s)
• Gap under entry door(s)
• Open vents
• Gaps under and to the sides of garage door
• Openings where water heater pipes enter drywall
• Opening where air conditioning lin enters wall
• Torn or missing crawl space cover
• Unharvested or fallen fruit
• Debris
• Uncovered trash cans
• Pet food left out
• Seed type bird feeder
• Wood Piles
• Hutches: Chicken, rabbit, etc.
• Storage sheds

How Norway Rats Enter the Home

Norway (sewer) rats have the ability to enter the home through the sewer lines. They find breaks in drain pipes caused by faulty joints, poor construction or by tree roots. Norway rats will burrow through the ground and will emerge into yards, under sidewalks, driveways, and enter buildings.

Norway rat access through a sewer line.

Norway rat control is also achieved by eliminating water, food and harborage sources. Although this species primarily nests in underground burrows, Norway rats may also establish nests in Algerian ivy, rubbish piles, utility sheds, storage boxes, wood piles and heavy shrubbery.

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Basic Rodent Proofing Measures

Substandard repairs and remodeling can alter a structure's rodent proofing. Repairs for rodent proofing are usually very simple and cost very little. Periodic inspection of your property should be conducted to insure that proper rodent proofing is still intact. A rat will enter a hole the size of a half dollar. A mouse will enter a hole the size of a nickel.

1. Subfloor space ventilation openings must be without holes and gaps.
2. Subfloor crawl space access door must be free of gaps.
3. At the junction of roof pitches, the overhanging roof may form a triangular recess which allows rat entry at the very back. Most of these areas are inaccessible.

1/4 inch hardware cloth, cement fill, and sheet metal are all excellent materials to use for sealing up gaps and holes.

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Environmental Management

Good environmental management practices supplemented by the wise use of rodenticides and proper trapping are the most effective approaches to rodent control. Environmental sanitation and good housekeeping are the first steps in a successful roof rat control program.

Woodpile management to discourage roof rat activity.

• Harvest all fruit as soon as it ripens
• Pick up all fallen fruit
• Store wood and lumber piles 18 inches above the ground and 12 inches away from walls
• Never leave pet food in metal containers
• Keep all vegetation well trimmed and away from roofs, walls, fences, poles, and trees
• These plant species provide harborage and should be avoided: Algerian ivy, blackberry, bamboo, Pampas grass, Bougainvillea, Oleander, and Italian Cypress

	BEFORE
	AFTER

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For assistance with any of these prevention techniques, or to schedule an inspection, please contact the district at (650) 344-8592. More information on our services can be found here.

For alternate methods to solve a rodent problem please visit the following pages:

• Rodent Trapping and Control
• Other Rodent Control Options

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