Add an extra roof to keep your bird house cooler.
In severely hot weather, if the inside of an Eastern Bluebird bird house gets too hot (above 107 degrees) it could harm the eggs.
It is sooo hot here today, with temps up to 96 and a heat advisory with heat index of 100-104 degrees. We always think of how to help the birds stay cool. One way is to air-condition our bird houses. We do this by putting an additional roof on the house. We nail on a piece of plywood, using long nails and only nailing them part way into the original roof. This leaves an airspace between the two roofs of about an inch. The second roof shades the first roof plus the airspace between the roofs acts as an insulator, keeping the bird house cooler.