So if squirrels weren't bad enough, let me introduce you to the raccoon family down the block. Just like the squirrels, they would love to move in as well. Raccoons won't wait for a invitation either. They will just move in without your permission. Yep, they will break in just like their mask suggest, little bandits. They will access your roof by a close tree branch, your deck, chimney, even climb up the down spout of your gutter to get access to the roof. Here they will rip your wooden shingles off or your roof vents to gain access to the attic. They will also climb down your chimney and have babies on the damper. I have also had a raccoon open the ash door and have the babies in the ash pit of the fireplace. Ah, home, sweet home!
Here inside the attic the female will have 4-6 babies. The female does all the raising of the young on here own. The male is gone and out of the picture. He will actually kill the babies if he has an opportunity to do so.
And just like squirrels, raccoons are not good housekeeper either. They will urinate and leave their droppings in your attic insulation. Their droppings are about the size of a small dog. Also they will usually pick a designated spot to use as a latrine. And it piles up over a period of time.