Advice Summary

CAREFULLY CAULK AND ADD two or three coats of paint to all houses. The objective is to provide a seal against moisture and to prevent drafts at the top where bats roost. Best colors in the South are light brown, possibly white or medium brown, ranging to dark brown or black in the North, probably black in Canada. Provision of at least a five-inch extension of the back board for a vertical landing platform, horizontally grooved at half-inch intervals, will help returning bats.

Most occupied houses face east or west, but additional experimentation with dark brown versus black, facing south, is recommended in the coolest climates. Half-inch-wide horizontal ventilation slots, about six inches above the entrance, extending clear across the house, as illustrated in the new Bat House Builder's Handbook, will reduce the odds of overheating on hot days. An overlapping tin roof may provide additional protection in the hottest areas. Our tests last summer showed that houses with at least partial sloping bottoms are more stable in temperature. This could prove useful, especially in the North, but be sure to allow enough slope to permit droppings to fall out.

We strongly encourage paired comparisons of differently treated houses, changing only one variable at a time, such as the amount of time or direction of sun exposure, color of house, closed or open bottom, internal roost space dimensions, construction materials, or habitat placement. After you have attracted your first bats, we encourage you to try your own unique designs, varying materials, color, and sun exposure.