How Do Squirrels Get Into Attics?
Squirrels are extremely agile, as you have probably noticed. They can easily grip and climb all sorts of materials - including the exterior walls of your home. Many squirrels can climb up trees and then jump onto your roof, which makes finding an access point that much easier. All they have to do is squeeze into a hole that is about an inch and a half. They are also able to find smaller holes and chew on the edges to make them large enough to squeeze into.
The most common spot that you will find squirrels gaining access is in your roof returns, the dark corner where the soffit around the home meets the roof. Roofers will leave these open, not thinking about the wildlife that could potentially use it for entry. While it is not nearly as common, they can also gain access through open garage doors, or even under stairs. So, if there is any open spot on your home, a squirrel will more than likely find it and use it to gain access to the home.