A nestbox provides safe haven for squirrels, especially younger ones or a mom with babies. As I'll show, I have evolved my nestbox design from lessons learned and tools and material available. As most will have different tools and material to work with, an exact duplicate of my nextbox may make the task difficult. If alterations or changes are needed, there are a few nestbox requirements that should be maintained.
Squirrels chew, and softwoods will disappear under their teeth. Hardwood (oak) makes for a durable nestbox, but is heavy, harder to work with, and more costly. At the minimum, make sure the entrance to the box has hardwood around it and the predator guard needs to be hardwood.
Use rust resistant fasteners, such as hot dip zinc coated nails. Stainless steel screws, often sold as deck fasteners, also work.
The entrance hole for a gray squirrel should be 2.5 inches in diameter
A predator guard should be placed inside the box under the hole. This is a ledge several inches deep. It is intended to prevent an animal from inserting its arm and grabbing any occupants. It may get its arm inside the hole, but should be unable to articulate it to grasp anything under the ledge.
Solid oak construction
Stainless steel screws used throughout
Both sides hinged for opening to allow for blow through spring cleaning
Predator guard 3/4 inch thick oak
Slant roof for rain drainage Porch under entrance hole plus roof overhang provide added security