How to Seal Your Attic Against Pests

Attics serve as the primary gateway for rodents, squirrels, and insects looking to turn your home into a nesting ground. Because most pests can squeeze through holes no larger than a dime, finding these entry points requires a detective's eye and a complete disregard for cobwebs. Success in this project means creating a structural barrier that is not only airtight but also physically impenetrable to teeth and claws. When done well, you transition your attic from an easy-access point to a fortified shell, effectively ending the cycle of infestation without relying solely on traps or poisons.

1. Find Every Light Leak. Go into the attic during the day, turn off all interior lights, and have a partner walk around the exterior with a bright floodlight. Watch for any beams of light filtering through the roofline, eaves, or vents.
2. Spot Weak Vent Screens. Check the screens on your gable vents for sagging, rust, or loose edges where animals could pry their way in. If the mesh is damaged, it needs to be replaced entirely rather than patched.
3. Cut Off Pest Highways. Trim all tree branches back at least six feet from the roofline to eliminate the 'bridge' pests use to reach your home. Also, clear away any climbing vines that provide a ladder to your gutters.
4. Install Chew-Proof Barriers. Cut 19-gauge or thicker hardware cloth to fit behind vent openings and over gaps larger than a quarter inch. Secure the cloth firmly with galvanized steel screws and washers.
5. Seal Remaining Cracks. Use a pest-blocking expanding foam or a high-grade polyurethane sealant to fill smaller cracks around plumbing stacks and electrical penetrations. Smooth the sealant with a putty knife for a clean finish.
6. Confirm the Seal. Re-enter the attic at night with a flashlight and check the perimeter one last time. If you see no light coming in from the outside, you have successfully closed the perimeter.