Rat droppings in the attic: how dangerous, and how worried to be

The short answer, from the people who track it

Rat droppings in the attic, and mouse droppings in insulation, are a health concern, not just a mess, and the reason has a name: hantavirus. Everything on this page comes from two official sources, the California Department of Public Health (CDPH) and the federal Centers for Disease Control and Prevention (CDC). We quote them closely and don't add medical advice of our own.

CDPH says Sin Nombre virus, the hantavirus that matters in California, "is spread by deer mice, which are found throughout California." People get infected by breathing in air contaminated by infected rodents, which is what happens when dried droppings, urine and nesting material are disturbed. CDPH also puts the risk in proportion: there are about 3 Sin Nombre infections reported in California each year. It's rare, and it's serious, and that's why the cleanup rules are so specific.

What about rats?

Most Bay Area attic trouble involves rats, so it's a fair question. The CDC says Seoul virus, a different hantavirus, "is carried primarily by Norway rats", that it "has been found in both pet rats and wild rat populations around the world, including the United States", and that infected rats spread it through urine, feces and saliva.

That's as far as the official sources go, and it's as far as we'll go. A dropping doesn't tell you which animal left it or whether that animal was infected. Treat every dropping in the attic the same way.

What not to do

The most important instruction is the one people break most often. CDPH says: "do not sweep or vacuum the area." The CDC says the same: "Don't vacuum or sweep rodent urine, droppings, or nesting materials." Sweeping and vacuuming throw tiny contaminated particles into the air at exactly the height you breathe.

That rules out more than a broom:

• No household vacuum and no shop vac.
• No leaf blower to "clear out" the attic.
• No dry brushing droppings off boxes before carrying them downstairs.
• No crawling around in soiled insulation to see how bad it is.

If you aren't going to clean up the way the next section describes, the right move is to leave it alone and close the hatch.

CDPH's steps for a small cleanup

For a small area, such as a few droppings by the hatch, on a shelf or on boxes you've already brought down, CDPH and the CDC give these steps:

1. Air it out first. CDPH: "Air out the space you will be cleaning for 30 minutes." The CDC says to open all doors and windows for 30 minutes before cleaning.
2. Wear gloves. The CDC specifies rubber or plastic gloves.
3. Soak, don't wipe dry. CDPH says to "spray the contaminated area with the disinfectant or bleach solution until very wet" and leave it for at least 5 minutes. The CDC's bleach mix is 1.5 cups of household bleach in 1 gallon of water (1 part bleach to 9 parts water), made fresh each time, or an EPA-registered disinfectant used as its label directs.
4. Wipe up wet. CDPH: "Use paper towels, a sponge, or mop to clean up the contaminated area."
5. Bag it. The CDC says to put dead rodents and nests, after soaking them, in two plastic bags and then in a covered trash can that's emptied regularly.
6. Wash your hands. The CDC: "Wash hands with soap and warm water after removing gloves."

Buildings that have been shut for a while

CDPH has a separate note for opening up a building that's been closed for a long time, like a cabin, shed or long-empty unit: air it out for 30 minutes or more before going in to clean, and "clean only with a wet mop or sponge." The reason is the same as above. "Sweeping or vacuuming stirs up mouse droppings and other rodent-contaminated materials."

When it's more than a few droppings

Both agencies treat a heavy infestation as a different job. CDPH says to "consider wearing a respirator (face mask) if cleaning heavily infested areas." The CDC's page has a section of special precautions for heavy rodent infestations and vacant buildings with large numbers of rodents. For people hired to do that cleanup, it lists coveralls, rubber boots or shoe covers, gloves, goggles and a respirator with HEPA filters, fit-tested under state and local rules, and it says those workers should contact their local or state health department, the state's occupational safety authority and the CDC.

The CDC also addresses insulation directly: "If exposed insulation is contaminated with urine and droppings, place it into plastic bags for removal."

Why a soiled attic isn't a weekend project

This part is our view, not the agencies'. CDPH's spray-and-wipe steps work on a floor, a shelf or the top of a box. They don't translate to an attic floor where droppings are mixed through inches of loose fill or batts you can't soak and wipe. Insulation in that state comes out, in bags, and the job looks a lot more like the CDC's heavy-infestation section than like a quick wipe-down. That means protective gear, a respirator and hours bent over in a hot, cramped space.

So if the droppings are spread through the insulation rather than sitting in one spot, don't do it yourself. Close the hatch, keep kids and pets out, and have it looked at. Our attic cleaning and sanitizing page explains how a contaminated attic is cleaned without dry sweeping, and insulation removal covers when the soiled insulation has to go.

If you feel unwell

CDPH says symptoms usually develop 4 to 42 days (1 to 6 weeks) after breathing contaminated air, and that early signs can look like other respiratory illnesses. If you have a fever or trouble breathing and you've been around rodents or rodent-contaminated material, CDPH says to "talk to a healthcare provider right away and tell them about your recent exposure to rodents."

Then keep them out

Cleaning up only lasts if the animals can't get back in. Rats in the attic covers how to tell what you have and where it's getting in, and rodent proofing explains how entry points get closed with metal. When you're ready for someone to look, book a free inspection or send us photos first.