Rodent Exclusion and Sealing in San Francisco
Exclusion means finding every opening a rat or mouse can use and closing it with material they can't chew. In an older San Francisco building that's usually the biggest part of the job. Trapping clears out the animals inside. Sealing keeps the next ones out.
The health department lists entry points as one of the things that keeps an infestation going, along with harborage outside and in, and food and water. Its guidance for building owners is to seal openings around pipes and conduits with materials like hardware cloth and copper mesh, and to close gaps bigger than a quarter inch around exterior doors and windows.
What Holds Up
UC IPM says rats chew through plastic, foam, wood and caulk. It recommends steel wool, wire screen or sheet metal for openings, galvanized expanded metal or wire cloth for vents, sheet metal over gnawed door edges and door sweeps or weather stripping at the bottom of doors. It also says to use half-inch mesh on vent screens and never lightweight chicken wire.
- Young rats fit under a door with a half-inch gap
- Seal cracks and holes bigger than a quarter inch
- Metal and wire cloth, not foam by itself
- Door sweeps on garage and basement doors
Where Old Buildings Leak
Foundation vents with rusted or missing screen. The gap under the garage door, especially on a sloped driveway where the door doesn't sit flat. Old pipe and gas line holes in the basement wall. The joint where a newer addition meets the original house. Utility lines coming in through the wood siding. Rear stairs and decks attached to the back wall. A rodent inspection maps these out.
Seal After the Rats Are Out
If you close every hole while rats are still inside, you trap them in your walls. Most companies trap first, keep an eye on the main entry and close it once the activity stops. Get the plan in writing, along with whatever warranty they give on the sealing.
Questions We Get
Can my landlord be required to seal the building?
The health department's guidance puts routine inspections and response to tenant reports on the owner. If rodents keep getting in and nothing happens, you can call 311 to file a complaint with the health department.
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