The entrance hole should be 1 1/2 inches in diameter for Eastern Bluebirds, or 1 9/16 inches if accommodating multiple bluebird species. This size allows bluebirds to enter while keeping larger birds, like starlings, out.
The box should have a floor size of 4" x 4" to 5" x 5" and a depth of 5-6 inches. The roof should overhang the entrance to protect against rain.
Use untreated, rot-resistant wood such as cedar, pine, or cypress, with a thickness of at least 3/4 inch. Avoid pressure-treated wood and materials that can harm birds.
Include ventilation holes near the top of the sides to allow airflow and prevent overheating. Ensure there are drainage holes at the bottom to keep the interior dry.
Design the house with a swing-open side or a removable roof for easy access to check for nests and clean out old materials after fledging.
Mount the box on a smooth pole to deter climbing predators. Consider adding a baffle below the box for additional protection.
Position the box 5-6 feet above the ground in an open area, facing southeast to receive morning sunlight and avoid harsh afternoon heat.