Rats or mice in the attic: signs, first steps and the order of the fix

Before anything else: don't touch the droppings

The instinct is to grab the shop vac. Don't. The California Department of Public Health's guidance for rodent droppings is explicit: "do not sweep or vacuum the area," because that can stir droppings and contaminated material into the air. Deer mice, which CDPH says are found throughout California, carry the Sin Nombre hantavirus. Infections are rare, about 3 a year in the state by CDPH's count, but serious.

So for now: close the attic hatch, keep kids and pets out of the attic and away from any droppings you've found elsewhere, and keep reading. If droppings have to be cleaned up somewhere you live, CDPH's cleanup steps and what it says about symptoms are on our page are rodent droppings dangerous.

Who's up there

Three animals account for most of the scratching in Bay Area ceilings, and a fourth is the one public health officials watch.

• Roof rats. Sleek, agile climbers with a tail longer than their head and body together, according to UC's Integrated Pest Management program. They nest above ground and move along fences and utility lines at dusk. They love citrus and avocados, often eating the fruit right on the tree. With mild winters and backyards full of fruit trees, much of the Bay Area suits them well. When the noise is overhead, roof rats are the likeliest culprit.
• Norway rats. Larger and stockier. UC notes they burrow along foundations and under woodpiles and debris. Indoors they tend to stay low, which in an older house on a raised foundation means the crawl space, the garage and the ground floor walls before the attic.
• House mice. Small enough to slip through very small gaps, and happy to nest in the insulation itself.
• Deer mice. UC describes them as having larger eyes than house mice, a white underside sharply divided from the darker back, and a furred tail. They're the species CDPH names as the main carrier of hantavirus in California. You won't tell a deer mouse from a house mouse by the droppings, so treat every mouse dropping with the same caution.

Squirrels, raccoons and opossums also end up in attics now and then. They're a different problem with different rules, so if that's what you have, ask for a wildlife removal service rather than assuming a rat program will cover it.

Signs it's rodents, not the house settling

Houses creak as they cool at night. Rodents sound different. Here's what to listen and look for:

• Noise after dark. UC notes that rats are mostly active at night and lists noises from the attic as a classic sign. Scratching or scurrying overhead, often along the edges of the ceiling where the eaves are, is the typical pattern.
• Droppings. By the attic hatch, along the tops of the walls, on stored boxes, in the garage. Look, don't touch.
• Runways in the insulation. Flattened paths and tunnels through the fluff.
• Rub marks. Greasy dark smudges where fur brushes the same beam, pipe or hole on every trip.
• Gnawing. Chewed wire jackets, shredded duct wrap, gnawed edges on vent screens. UC lists gnawed fruit and nuts in the yard as another giveaway.
• A sharp smell. Rodent urine gives off an ammonia smell that's strongest on warm days. If a smell is your main clue, our attic smell page matches odors to causes.

The order of the fix

This is where people lose money: doing the right things in the wrong order. The sequence that holds up has four steps.

Step one: get the animals out

Trapping and removal come first, and they're a pest control company's job. In California, controlling household pests is structural pest control. The Business and Professions Code defines household pests to include "rodents, vermin, and insects," and the Structural Pest Control Board oversees the companies that do this work. Ask a pest control company for an inspection and a plan, and ask how they'll confirm the activity has stopped.

Step two: close the way in

Trapping without closing the gaps is a subscription, not a fix. UC calls exclusion "the most successful and longest-lasting strategy" for keeping rodents out of buildings, and its working rule is to seal every opening larger than a quarter inch. On a Bay Area house that means eave gaps, torn vent screens, gaps at roof-to-wall joints, pipe and cable holes, and in older homes the foundation vents and crawl space door. The barrier has to be metal (hardware cloth, sheet metal, packed metal mesh), because rats chew through foam. Our rodent proofing page covers where we look and how the openings get closed.

Timing matters. Seal the house while rats are still living inside, and you've locked them in with your wiring. That's why step one comes first.

Step three: clean up what they left

Droppings, urine and nesting material soak into insulation, and soiled insulation can't be cleaned in place. It comes out, the attic is sanitized, and the work is done without dry sweeping. See attic cleaning and sanitizing for how the cleanup runs, and insulation removal for taking out the soiled insulation.

Step four: then insulate

New insulation goes in last, into a clean attic that animals can no longer reach. Do it earlier and you've just built them a warmer nest.

Why California homes lean on sealing, not poison

California has some of the tightest limits on rat poison in the country, and that changes the playbook.

• 2021: AB 1788, effective January 1, 2021, restricted four second-generation anticoagulant rodenticides (brodifacoum, bromadiolone, difenacoum and difethialone).
• 2024: AB 1322, effective January 1, 2024, added diphacinone, a first-generation anticoagulant.
• 2025: AB 2552 restricted the remaining first-generation anticoagulants, chlorophacinone and warfarin, from January 1, 2025.

The Department of Pesticide Regulation now says most uses of both first- and second-generation anticoagulant rodenticides are prohibited, that the "prohibitions include residential or home uses," and that the exemptions are for things like water infrastructure, public health agencies and certain farms and food facilities. Rules are still under review at the department, so check its site for anything newer than this page's verified date.

What it means at home: the old routine of tossing bait blocks into the attic is mostly gone, and a pest company works with the tools it's allowed to use. That puts more weight on the parts that don't involve chemicals at all: closing the openings, and taking away food and cover outside. UC's pest notes suggest cutting back tree limbs that touch or overhang the roof, pulling ivy off walls, and picking up fallen fruit.

What it costs and what comes next

Costs depend on how many openings there are, how much insulation is soiled and how big the attic is. We keep Bay Area market ranges for cleanup, rodent proofing and new insulation on the cost page rather than repeating them here.

Once the pest company has confirmed the activity has stopped, the next step on our side is a free inspection of the roofline, attic and crawl space. Book it here.