Everyone knows what a bird house or bird box is--an artificial box (manmade) for birds that like to nest in tree cavities such as bluebirds, tree swallows, wood ducks, kestrels, sawhet and screech owls. Natural tree cavities are in short supply and these manmade boxes can really help during the breeding season.
Roosting boxes are similar and serve the same birds, but have a different purpose. These boxes are used in the winter and serve to protect birds from the worst of cold weather. Uniquely, while only one family of birds will use a nest box, 20 or more birds may use a roosting box.
The big differences between nesting and roosting boxes are:
1. That roosting boxes are sealed against heat loss while heat dissipation is critical for nest boxes.
2. The entrance for a roosting box is on or near the bottom of the box and not near the top like in a nesting box.
3. A nesting box is oriented to the north to minimize radiant heat from the sun. A roosting box is oriented to the south to maximize the sun's heat.
While it is true that bird boxes will be used as roost boxes, roost boxes will serve more birds and are better designed for winter roosting.
Click here for plans for a large box or here to see plans for making bluebird box-sized roosting boxes. And here is a link to a website with a plan for a large horizontal box (18 inches long) like the one below.