First, you will need to evaluate your home. Go around the outside of your house. Look for entry points and remember that squirrels do not need a very large opening to enter your house. Ensure that you look for openings that are on the roof of the house and under the soffit and fascia. Make a list of every possible squirrel door that you find.
Second, you will need to purchase materials to prevent the squirrel entry in each of the openings. Some openings are not critical and can be sealed with expanding foam. Other openings are necessary for proper roof performance. If you seal the entire roof, you will have problems with moisture buildup and possible ice dams if you live in a freezing climate. If you aren’t familiar with roofing systems, you will want to talk to a professional before sealing holes with airtight materials. Self expanding foam is great for small holes and simple to use. You simply have to insert the hose into the gap, squirt the foam and like magic the foam grows to fill the hole and hardens. It doesn’t get any easier than that. For holes that are necessary for airflow, you can use a metal mesh material to prevent entry. All of these materials can be purchased at your local big box home improvement retailer. If you don’t have a large hardware store in your area, sites like Amazon or Wal-Mart carry these items and you can order them over the internet.
Finally, once you have evaluated your home, purchased your materials, and determined which holes can be sealed and which ones are necessary for air flow, you are ready to install. Some of these steps are easy and some should be handled by a professional installer. If you are not sure or hesitant with any of the materials, you should play it safe and let a pro install it. Make sure to be especially careful with any installations that require you to be on a ladder. It is easy to forget where you are and lose your balance. A fall from a second story height could easily cause serious injury or even death.