Most homeowners never think twice about what’s behind their walls. Insulation is supposed to be clean, dry, and untouched once it’s installed. Unfortunately, this isn’t always the case. The photo above shows fiberglass insulation removed during a cleanup. What you are looking at isn’t dirt or construction debris, it’s nesting material, urine staining, and droppings embedded into the insulation after mice gained access to the wall cavity. This type of damage is far more common than most people realize.
Why Mice go straight for insulation
When mice enter a home, insulation is one of the first places they target. Fiberglass insulation offers
- Warmth
- Protection from predators
- Easy tunneling
- Material for nesting
Fiberglass doesn’t stop mice- it’s perfect nesting material for them. Once they are inside, they move freely through wall cavities, compressing insulation as they go and creating hidden nesting areas.
What happens behind the wall
The damage caused by mice inside insulation often goes unnoticed for years. Unlike a kitchen infestation, there may be no visible droppings or sounds once activity slows down. This is because in most basements, the entry points are along the rim joist, so unless they climb down the the basement floor there may be no obvious signs of them,
Behind the wall, however, several things are happening:
- Insulation loses effectiveness: Tunnels and nesting collapse the fiberglass, reducing its R-value and increasing heat loss
- Urine and droppings contaminate large areas: Fiberglass absorbs moisture and odor. Once contaminated, it cannot be cleaned or deodorized.
- Odors spread through the home: Wall cavities act like air channels, allowing smells to move into living spaces
- Health concerns increase: Mouse droppings and urine can introduce bacteria and allergens back into the home environment
Why traps alone don’t fix the problem
Many homeowners start with traps or bait stations. While these are good tools to control the existing population, the damage will remain indefinitely. To truly mitigate the issue, the homeowner must:
- Seal entry points
- Remove contaminated insulation
- Eliminate odor sources
- Prevent future infestations
Unless access points are identified and cut off, new mice will follow the same scent trails and continue entering the home. Mice are a seasonal issue and will return given the opportunity.
The Correct way to address mouse damage
1. Full Home Mouse Exclusion
Every exterior entry point—no matter how small—is identified and sealed, which prevents new mice from getting inside.
2. Removal of Contaminated Insulation
Insulation like what’s shown in the photo cannot be salvaged. Once it has been used for nesting or contaminated with droppings, it must be removed.
3. Droppings Cleanup and Sanitation
Affected areas are cleaned and sanitized to reduce odors and health risks.
4. Replacement with Spray Foam Insulation
Spray foam is especially effective following mice damage because it eliminates the conditions rodents rely on to thrive.
Spray foam insulation:
Air seals wall cavities
Does not support nesting
Blocks rodent travel paths
Improves energy efficiency
This combination not only resolves the mouse issue but also prevents it from returning, which is why we choose it as our primary insulating material.
How FVEPC can help
Fox Valley Environmental Pest Control has been helping homeowners in Kane, DuPage, and surrounding counties rid their homes of mice and the damage they cause to insulation for over 35 years! Our Purdue and State-certified technicians are trained to identify and skillfully mitigate the mouse damage to insulation, and replace it with a clean and long lasting solution. Call FVEPC today for a free quote!
