Squirrels shred fiberglass and cellulose insulation to build nests, and while they are up there they leave droppings and urine through everything. Before you touch any of it, make sure the squirrel is actually gone, and check the wiring. Insulation is the mess you can see. Chewed wires are the fire hazard you cannot.
Evict the squirrel first
No point cleaning if the squirrel is still inside. Watch and listen for a couple of days. If you still hear scratching, put a one-way door over the entry hole, or set a live trap near it. Only start the cleanup once the attic has been quiet for a few days straight.
While you are up there, check the wiring. Squirrels chew the insulation off electrical wires. Look for exposed copper, gnawed sheathing, and nesting material wrapped around cables. If you see damage, get an electrician to look at it before you bury everything under fresh insulation again.
Gear up
Squirrel droppings and nests can carry bacteria and parasites. You need:
- An N95 or P100 respirator, not a cloth mask.
- Nitrile or rubber gloves.
- Safety goggles.
- A disposable coverall or long sleeves and pants.
- Good lighting and a sturdy ladder.
And do not use a regular household vacuum. It blows the fine particles right back into the air. Use a HEPA vacuum rated for this kind of cleanup.
Removing the contaminated insulation
- Lightly mist the insulation with water from a spray bottle so dust does not go airborne.
- Vacuum up the loose debris, droppings, and nesting material with the HEPA vacuum.
- Bag the insulation in heavy-duty bags and double-bag it.
- Dispose of it the way your area handles this kind of waste.
Cleaning and sanitizing
Once the space is empty, spray down every surface with a disinfectant or a bleach solution of about one part bleach to ten parts water, and let it sit long enough to do its job. If urine has soaked into the plywood, an enzyme cleaner made for animal waste does a better job than bleach at breaking down the smell.
Sealing the entry points
This is the step that stops the whole thing from repeating. Seal every gap with galvanized hardware cloth, and pack pipe and wire openings with steel wool before foaming them. Secure the mesh with screws and washers, not staples, because squirrels pull staples loose.
Installing new insulation
Blown-in cellulose treated with boric acid holds up better against pests than plain fiberglass and is less appealing as nesting material. Match the insulation value to your climate, and if you are not comfortable doing the install, this is a reasonable step to hire out.
Frequently Asked Questions
No. Once it is contaminated with droppings and urine, patching just leaves a biohazard behind and does nothing for the insulation value. Remove and replace.
It varies a lot with the size of the attic and how bad the contamination is, plus whether you hire out the removal, the install, or both. Get quotes if the damage is extensive.
You can, but I would not. Squirrels tear fiberglass apart easily and use it for nests. Cellulose with boric acid is more resistant and less attractive to them.
Listen for a couple of quiet days, check for fresh droppings near the entry point, and do the paper towel test: crumple a towel into the hole and see if it is still there a day or two later.
