A soft scratching overhead after the house goes quiet. Shredded insulation near the attic hatch. Small droppings on top of the box of holiday lights. Mice in attic spaces are a classic cold-weather problem, and they are much easier to handle once you know what you are hearing, where they got in, and what to do first.
This guide covers the signs, how mice get into an attic, and a step-by-step plan to deal with them and keep them out.
The Short Answer
Find and seal the entry points, deal with the mice that are already inside (with snap traps or a licensed pest control professional), clean up safely using CDC guidance, and then keep checking through the winter. A scent repellent can add a layer near entry points and stored items, but it will not remove mice that are already living in your attic.
Why Mice Move Into Attics When It Gets Cold
According to the University of California Integrated Pest Management Program (UC IPM), house mice that live outdoors frequently enter homes in autumn, when nighttime temperatures drop. The National Pest Management Association (NPMA) estimates that rodents invade about 21 million U.S. homes each winter.
An attic is quiet, sheltered, and full of soft nesting material. The NPMA notes that mice burrow into insulation and that deer mice may nest in attics and storage boxes.
Signs of Mice in Attic Spaces
Noises at Night
UC IPM says mice are active mostly at night, so scratching or scurrying overhead is easiest to notice once the house is quiet. The NPMA lists strange noises in attics as a warning sign.
Droppings
Mouse droppings are about 1/8 to 1/4 inch long, rod-shaped, with pointed ends, according to the NPMA. Check along the attic edges, on stored boxes, and near the hatch. Our guide on what mouse droppings look like covers identification in more detail.
Nests, Odor, and Rub Marks
UC IPM describes nests of finely shredded paper or other fibrous material, plus a musky odor in larger infestations. Look for tunneled insulation, chewed boxes, and oily rub marks along beams. The NPMA warns that one mouse you see is likely one of many out of sight.
How Do Mice Get in Attic Spaces?
Mice do not need to start at ground level. UC IPM describes house mice as excellent climbers that can run up any rough vertical surface and run along wire cables. Iowa State University Extension recommends checking openings around the roof, including attic vents, for that reason.
The CDC lists these outside spots to inspect:
- The roof, including rafters, gables, eaves, and soffits
- Attic and crawl space vents
- Holes where electrical, plumbing, cable, and gas lines enter
- Windows and doors, especially those without weather stripping
According to the CDC, mice can fit through a hole the width of a pencil, about 1/4 inch. Not every attic mouse comes in through the roof, either. Gaps around pipes and wires inside the house can lead up through the walls. For the full list of entry routes, see how mice get into your house.
How to Get Rid of Mice in Attic Spaces: Step by Step
Step 1: Inspect Inside and Out
Check the roofline, vents, and utility lines from outside, and note branches or vines touching the house. UC IPM recommends thinning plants that climb up buildings. Inside the attic, look for droppings, nests, and daylight through gaps.
Step 2: Seal the Gaps
The CDC recommends filling small holes with steel wool held in place with caulk or spray foam, and using hardware cloth, lath screen, metal sheeting, or cement for larger openings. UC IPM warns that plastic screening, rubber, vinyl, expanding foam, and wood are gnawable and do not work on their own. For gaps high on the roof, hire a professional rather than climbing.
Step 3: Deal With the Mice Already Inside
The CDC recommends traditional snap traps and advises against glue traps and live traps. UC IPM suggests placing traps close to walls, where mice travel, and spacing them about 10 feet apart, since house mice seldom go more than 30 feet from their nest. Keep traps away from children and pets, check them often, and continue until you stop catching mice.
Step 4: Clean Up Safely
Follow the CDC cleanup steps: wear rubber or plastic gloves, do not sweep or vacuum droppings or nests, soak them with a bleach solution (1.5 cups of household bleach per gallon of water) or a disinfectant for 5 minutes, then wipe up with paper towels. The CDC calls for special precautions with heavy infestations, so badly soiled insulation is a job for a professional.
Step 5: Make the Attic Less Inviting, Then Keep Checking
Swap cardboard boxes for resealable plastic bins, which the NPMA recommends to cut down on nesting spots, and keep food, bird seed, and pet food out of the attic. Look in every few weeks until spring. Fresh droppings after sealing usually mean a gap you missed.
What About Mothballs and Ultrasonic Devices?
Mothballs are a registered pesticide, and the label sets the rules. EPA notes that registered mothball labels specify the use site as "air-tight containers and storage closets," and that using a pesticide in a manner inconsistent with its labeling is generally unlawful. Scattering them across attic insulation is not what those labels describe.
On ultrasonic devices, UC IPM says ultrasonic sound has very limited use in rodent control because it is directional, does not penetrate behind objects, and loses intensity with distance.
When to Call a Professional
The NPMA recommends a professional for mice in walls and attics. Call a licensed pest control professional if activity continues after sealing and trapping, if entry points are high on the roof, or if you are not sure what animal you are hearing.
Cheat Sheet
- Night scratching, droppings on boxes, and tunneled insulation are the main signs.
- Mice climb well, so check the roofline, soffits, gables, and attic vents.
- Seal gaps of 1/4 inch or more with steel wool plus caulk, or with hardware cloth or metal.
- Use snap traps along walls, about 10 feet apart, out of reach of kids and pets.
- Never sweep or vacuum droppings. Wet them with disinfectant first.
- Store attic items in lidded plastic bins, not cardboard.
- Keep checking every few weeks until spring.
Where BioGuard Fits
We sell BioGuard Natural Rodent Repellent, a pack of 12 scent balls infused with peppermint and cinnamon essential oils. In an attic setting, it is best used near sealed entry points and around stored items, after the mice inside have been dealt with. It is a repellent, not a removal product, and it does not replace sealing. Replace it every 4 to 6 weeks, keep it away from children, pets, and food, and expect results to vary.
Frequently Asked Questions
How do I know if I have mice in my attic?
Look for small droppings, tunneled insulation, chewed boxes, a musky smell, and scratching sounds at night.
How do mice get in the attic?
Usually through small gaps along the roofline, soffits, gables, and vents, or up through wall voids from lower floors. According to the CDC, a gap about 1/4 inch wide is enough.
Will mice in the attic leave on their own?
Do not count on it. UC IPM notes that mice can breed year-round when food and shelter are stable, and that a female may have 5 to 10 litters a year.
Can mice in the attic get into the rest of the house?
Yes. Gaps around pipes and wiring that connect floors work in both directions. If you hear activity lower down, read our guide to mice in walls.
Sources
- CDC, How to Seal Up to Prevent Rodents
- CDC, How to Trap Up to Control Rodents
- CDC, How to Clean Up After Rodents
- UC IPM, Pest Notes: House Mouse
- Iowa State University Extension AnswerLine, Preventing Unwanted House Mouse Guests
- NPMA, How to Get Rid of Mice in Walls and Attics
- NPMA, Rodent Prevention Tips for Fall
- NPMA, Deer Mice
- NPMA, Pests in the Garage (plastic containers instead of cardboard)
- U.S. EPA, Pesticide Labeling Questions and Answers (mothball use sites)