Use untreated, rot-resistant wood like cedar, pine, or redwood. Avoid pressure-treated wood, as the chemicals can be harmful to birds. Ensure the wood is at least 3/4 inch thick for durability.
Construct the house with an entrance hole diameter of 1 1/2 inches for Eastern Bluebirds, positioned about 2 inches from the top. The box should be 5-6 feet high and have a floor size of about 4" x 4".
Include ventilation holes near the top and ensure the floor has drainage holes to keep the interior dry. Cutting about 1/2 inch off each corner of the floor helps with drainage.
Do not add perches to the entrance. They can provide a foothold for predators to reach inside the box.
Create a hinged or removable roof for easy access to clean out old nesting materials after the breeding season.
Use wood glue along with nails or screws to ensure a sturdy build. Pre-drill holes to prevent the wood from splitting.
Paint or stain the exterior with non-toxic products to protect against the elements, but leave the interior unpainted. Ensure the roof has an overhang to protect the entrance from rain.