Constructed of cedar, the side opens easily for monitoring and cleaning. A removable plexiglas panel prevents disturbing the nest when the side is opened. Interior predator guard. Dimensions: 5-1/2" W x 8-1/4" D x 13" H. Floor space: 5-1/2" x 3-5/8". North American Bluebird Society approved. By Songbird Essentials.