Birdhouse basics

Our lake association plans to build several bluebird houses. How big should I make the entrance, and how high off the floor of the birdhouse should it be located?
—Dick Webber, East Jordan, Mich.

The U.S. Fish and Wildlife Service recommends making bluebird houses 5" square and 9" high on the inside, with a 1¹⁄₂ " hole 5" above the floor. Leave the birdhouses unfinished both inside and out, and mount them 4–8' above the ground. If your group plans to follow up by helping house other bird species, refer to the chart below to guide your designs.