Most homeowners picture one big hole. In practice, rodents get in through several small gaps, many of them up high or hidden behind plants. The CDC notes that a mouse can fit through a hole the width of a pencil, about a quarter of an inch. Rats need a little more room, about half an inch, which is still smaller than most people expect.
Up high: the roofline
In Los Angeles the most common rat is the roof rat, a climber. It reaches the roof along tree branches, palms, ivy, fences and utility lines, then looks for a way in. Check:
- Attic and gable vents with torn, rusted or missing screens.
- Gaps where the roof meets the fascia, especially at corners and where two rooflines join.
- Roof returns and eaves, where a small gap is often hidden from the ground.
- Openings around plumbing vents and pipes that pass through the roof.
- Chimneys without a cap or with a damaged one.
Down low: the foundation and crawlspace
The Norway rat is a burrower and usually comes in at ground level. Check:
- Crawlspace vents with broken or missing screens.
- Gaps between the foundation and the ground, and cracks in the foundation itself.
- Holes where pipes, wires and cables enter the house, like the gas line, the air conditioning line set, cable and phone lines.
- Weep screeds and gaps under siding near the base of stucco walls.
Not sure which rat you're dealing with? See roof rats vs Norway rats.
The garage and the doors
- Garage doors with a worn or chewed bottom seal, or a gap at the corners.
- The door from the garage into the house, which often has no sweep at the bottom.
- Dryer vents with a missing or stuck flap.
- Pet doors left open at night.
Inside the home
Rodents that are already inside move through the walls along pipes and wires. The CDC lists places worth checking indoors: around pipes under sinks and washing machines, behind and under kitchen cabinets, around the fireplace, and around appliances. Droppings or grease marks near any of these show you a route they use often.
How entry points are sealed
The CDC recommends steel wool for small holes, held in place with caulk or spray foam, and lath screen, metal, cement, hardware cloth or metal sheeting for larger ones. Foam or caulk on its own isn't enough, because rodents chew straight through it.
A proper job follows an order:
- Inspection. A technician checks the roofline, attic, vents, crawlspace and garage and photographs every entry point. See rodent inspection.
- Removal first. The rodents already inside are removed before the last openings are closed, so none are sealed in to die in a wall.
- Sealing every gap, not only the obvious one. Leave one open and they find it. See rodent exclusion.
What you can do today
- Trim branches, palms and ivy back from the roof and walls.
- Keep firewood, boxes and clutter away from the outside of the house.
- Don't leave pet food or fallen fruit out overnight.
- Note where you hear noises or find droppings. If it's overhead at night, read noises in the attic at night.
Get it looked at
Tell us where you're seeing signs and we'll connect you with a state-registered pest control company that serves Los Angeles County. Start with rodent proofing, or call the number at the top of the page.
More guides
- A dead rat smell in the wall: what to do
- Rats chewing your car wires: what's going on
- Mice in the walls: what the sounds mean and what to do
This guide is general information, not a substitute for an on-site inspection. SealWell is a referral service, not a contractor.
