Reviewed by William "Willy" Vizcarrondo, NYS DEC Certified Commercial Pesticide Applicator C1825832. Updated September 23, 2026.
Short answer
Through the weak spots at the roofline: loose siding, damaged vent screens, rotted fascia boards, the gap at the roof edge and construction gaps at dormers, reached from an overhanging branch. Penn State notes squirrels find their way into buildings through loose siding or ventilation screens and chew siding and under eaves to make openings for their nests.
The roofline, from a tree. Gray squirrels are climbers and jumpers, and Penn State's exclusion advice to trim branches 6 to 8 feet away from buildings tells you how they arrive. From the roof they find the fascia board that's soft from a clogged gutter, the gable vent with torn screen, the ridge vent or turbine with a gap, the soffit return where two rooflines meet, and the hole a previous animal chewed. Where there isn't an opening, they make one. Penn State notes they chew siding and under eaves to make openings for their nests, and a squirrel can turn a small gap into a hole it fits through quickly.
Warmth and a nursery. Penn State notes gray squirrels breed in mid-December or early January and again in June, with two litters of one to eight pups a year, and an attic is a dry, protected den for both. That's why the noise starts in late winter and again in early summer, and why it's overhead in the morning and late afternoon; most tree squirrels are diurnal. If the running is at night, Penn State notes flying squirrels are the only squirrels active after dark, and they're small enough to get through gaps the other squirrels can't. Once inside, the damage starts. Penn State notes squirrels chew on insulation and the insulation around wires, which is the fire risk that makes an attic squirrel more than a noise problem.
One-way doors, then metal. Penn State's exclusion methods are one-way doors to let squirrels out and prevent them returning, sealing openings with heavy half-inch wire mesh, trimming branches 6 to 8 feet from the building, and metal collars on trees and poles they use to climb. The order matters: the door goes on the main entry, the other openings get sealed, the squirrels leave over a few days, and then the door comes off and that hole gets sealed too. Sealing everything at once with squirrels inside means chewing, in a new spot, from the inside out. In the breeding windows the attic gets checked for a nest of pups before the door goes on.
The oak-heavy North Shore towns, Huntington, Cold Spring Harbor, Dix Hills, Setauket, produce most of the squirrel attic calls, almost always from a branch touching the roof. In the Nassau capes and colonials it's the fascia behind a gutter that's been overflowing for years, in Levittown, Wantagh and Massapequa. Bobby Bugs finds every opening, installs the one-way door, seals with hardware cloth and metal flashing, and the wildlife nesting removal carries a 6-month written guarantee with a free estimate.
Related
Fast, light running and scratching overhead in the early morning and late afternoon, sometimes the sound of a nut rolling across the ceiling, and gnawing. Nighttime running that sounds the same is flying squirrels. Slow, heavy thumping at night is a raccoon.
Not while it's working for them. A squirrel that has a dry den and a route to the yard stays, raises pups there, and comes back each season. Removing the branch and closing the hole is what ends it.
Through wood, yes. They chew fascia, soffit, cedar shakes, plywood sheathing and vinyl or wood siding, which is why Penn State's exclusion material is heavy half-inch wire mesh, not caulk or foam. They can't chew through metal flashing or hardware cloth fastened properly.
Still not sure? Call (516) 509-6001 and we'll tell you what you're dealing with.