Removing mice from blown-in attic insulation is time-consuming, can be dirty and smelly, and can be costly. It involves sealing off access into the attic, removing the mice that are there, cleaning and disinfecting the space, and replacing the insulation.
Getting rid of mice also has to be done safely. Mice spread diseases that can make humans very ill and even cause death.
Why Mice Are In the Attic
Mice are curious and always searching for safe, snug, and warm nesting sites. Attics filled with blown-in insulation provide an excellent option–from the mice’s point of view. As long as there is a ready food source. Mice are omnivorous and will eat and chew on almost anything including wood and electrical wires.
Mice are good climbers and can get through a hole as small as a dime or a crack not much bigger than a quarter inch. Storing anything edible in the attic–like pet food or candy for Halloween–only encourages them to take up residence. They can get water from condensation on pipes and the roof deck.
Signs of Mouse Infestation
Some of the indications that the attic has a mouse problem include:
- Feces. Mouse droppings are black and about the size of a rice kernel. Found around food sources, nesting areas, or in a trail between the two.
- Noise. Mice are nocturnal. Attic noises–especially in the evening–should be investigated.
- Tunneling. Mice like to tunnel into or under insulation for safety and nesting sites. Tunnels about an inch in diameter usually indicate mice.
- Signs of Chewing. Rodent teeth grow continuously. They need to gnaw on things to wear their teeth down. Gnaw marks may appear on rafters/trusses, electrical wires, ducts, or almost anything solid.
How To Get Mice Out and Keep Them Out
Removing mice and keeping them out requires planning and attention to detail. All possible entrance holes have to be sealed, mice and contaminated insulation removed safely, and new insulation installed. The result should be a clean, odorless, and mouse-free attic.
Mouse-Proof the Attic
Inspect the entire roof and overhangs for holes. Pay particular attention to the wall or roof penetrations and corners where wood meets wood. The sealant that was originally used around pipes and vents gets old and separates. Wood expands and contracts because of moist and dry times. Soffit vent screening may be torn or non-existent. Fascia boards behind gutters could have rotted away–leaving holes leading directly into the attic.
Check the roof–especially penetrations, ridge caps, and third gable junctions. Framing in these areas often has gaps and old shingles curl and separate–leaving openings.
Install tight-weave steel mesh over large holes like soffit vents. Most smaller holes can be filled with steel wool. Then caulked, foamed, or covered with stucco patch. The steel wool is the second line of defense in case the foam or caulking fails. Mice may chew on it a bit, but swallowing small sharp wire shards will likely kill them.
Fill all the holes–even those that appear too small–to prevent them from being gnawed larger. Holes too small for mice invite insects.
Eliminate the Invaders
Once the attic is sealed, get rid of the mice inside. Some of the options include:
- Snap Traps. Almost always kill instantly.
- Live Traps. Mice must be killed after trapping, released outside, or donated to someone with pet snakes.
- Electrocution Traps. Battery operated.
- Glue Traps. Slow lingering death for trapped mice.
- Rodenticides. Poisons like Warfarin. Slow-acting. May leave carcasses to rot in wall cavities leaving a foul odor.
Place plenty of traps in the attic close to suspected food sources, tunnels, dark corners, or where there are lots of feces. Bate with peanut butter, a gummy bear, a marshmallow, or bacon. Check and empty the traps daily. After several days of empty traps, it is fairly safe to assume the mice are gone. If the infestation is bad enough, it may take a couple of weeks to eliminate all of the mice.
Clean Up The Attic
Mice can carry up to 30 different diseases–including listeria and Hantavirus. Hantavirus and some other rodent-borne diseases are carried in rodent feces and urine. Cleaning distributes particles into the air. Wear personal protective equipment including a full respirator and disposable gloves, a hazmat-type coverall, and head covering. Take it seriously. Some of these diseases kill. Hantavirus Pulmonary Syndrome has a mortality rate of 38%.
Mix 10 parts water to one part bleach in a garden sprayer and wet the insulation. Pay particular attention to nesting areas, feeding areas, and areas with the most feces. This solution weighs down any particles that may become airborne and kills germs, viruses, and bacteria.
To ensure a clean attic remove and dispose of all of the insulation. The most efficient method involves renting or hiring a vacuum truck. Another option is to rake up the insulation and bag it. This is a long process that runs the risk of disturbed insulation dust spreading throughout the house as the bags are carried out.
Use the same water/bleach solution to lightly spray the entire attic floor. Do not soak it. Wipe down any surface that is heavily covered with mouse feces and urine. To be absolutely sure, use undiluted bleach. The bleach sanitizes the area and inhibits mold growing on the urine.
Replace the Insulation
Once the attic is dry, replace the insulation with blown-in insulation, spray foam insulation, or batt insulation. All insulation can be installed by a contractor or as a DIY project–including DIY spray foam. Make sure to know how much insulation you need and how deep it should be.
Check the Rest of the House
A mouse infestation in the attic could migrate into the rest of the house. They can move down to the main floor and basement through holes drilled for plumbing and electrical wires. Eliminating them from the attic may push mice into other areas. Make sure they are completely gone.
If killing mice and cleaning up the mess they make is not a project for you, or the infestation appears extensive, call a professional pest control company to handle the job.