Ventilation Holes in Eaves are the Entry Points
It is said that small rodents, including mice and rats, can fit through a hole the size of a nickel. Obviously, they'll be able to fit through unprotected ventilation holes in your eaves. Many homeowners are not even aware that such holes exist. These holes are essential for attic ventilation, so you can't just slap wood over the top of them. In fact, even wood may not repel rats, mice, and birds--many of which can easily chew through wood. The answer is to cover the holes with flexible metal mesh called hardware cloth. This will keep out pests without restricting airflow through the vent holes.
How to Cover Attic Ventilation Holes: Step 1
Set up an extension ladder to reach the ventilation holes along the eaves. Inspect the holes with a flashlight to make sure they are clear of nest material or other obstructions. If necessary, clean out the holes to ensure proper airflow.
Measure the area to determine how much hardware cloth you'll need. The cloth should extend at least 1" beyond the holes.
Purchase galvanized hardware cloth with a grid (mesh) size of 1/8" or 1/4". Hardware cloth also comes in 1/2" mesh, but that is too large for barring rodents. Do not purchase chicken wire (sometimes called poultry netting), which has thin wire and large openings.
How to Cover Attic Ventilation Holes: Step 2
Cut the hardware cloth to size, using aviation scissors or standard tin scissors. Whenever possible, cut closely along the side of a wire to prevent having edges with sharp protruding ends. Wear gloves to protect your hands from the sharp metal.
How to Cover Attic Ventilation Holes: Step 3
Place the cut piece of hardware cloth over the ventilation holes and secure it with roofing nails. Drive a nail every 2" to 3" along the edges, ensuring the cloth lies flat to the wood surface.