Your insulation needs to be removed along with the droppings, as it'll carry some of its toxicity if left in your attic. Removing old insulation and replacing it with new ones will not only rid your home from any rodent infestation and mold, but also improve its energy efficiency and overall air quality.

Should you remove old cellulose insulation?

We're installing new windows, new siding, and adding insulation to our homes, especially in the attic. ... Expert contractors that specialize in insulation advise that removing old fiberglass insulation is best before installing new cellulose insulation because of possible mildew, mold, or rodent excrement.

Why is cellulose insulation bad?

Cellulose insulation is treated with fire retardants such as ammonium sulfate, borax, and boric acid to meet all governmental safety requirements. ... Unsurprisingly, this causes cellulose to have a higher fire rating than faced fiberglass insulation.