Bathouse on south facing gable of house

We finally put up the bathouse we built a few years ago.  Hopefully, a family of bats will discover it and take up residence, and take advantage of the bounty of insects we have available for them.

To install it, I ended up buying a bent metal joist hanger and cutting it so I ended up with two angle pieces I could nail into the sides of the bathouse, and then used a large nail hole on each piece to set it on two nails in the trim.

I didn’t design the bathouse itself; the plans came from Bat Conservation International (currently located here [PDF]), and I wrote an article about constructing this back in 2007 for Green Options (which is now archived among the articles).  The one modification I came up with was to use some metal drip edge material as a metal roof for the bathouse.  I cut a length of it and nailed it on with a couple roofing nails.  It ought to be more than adequate for the bats.

According to BCI, “Bat houses can be installed at any time of the year, but they are more likely to be used during their first summer if installed before the bats return in spring.”  I don’t know if we got this up in time, but it’s got good orientation,

The original article text is included below the cut, if you want to read the whole thing.

Weekly DIY: Build a Bathouse

Bats are wonderful creatures, though they are often misunderstood. Bats are especially good at helping to control insects. Some bats eat as many as 500 to 1000 insects in a single hour. So having a few flitting around can be a wonderful way to reduce the nuisance of insects in your yard without resorting to chemicals and poisons.

To encourage bats to settle near your house and bring their insect devouring prowess to work for you, a bat house is a relatively easy project that provides a place for the bats to nest. In order to be attractive to bats, a bat house needs to be narrow. In the wild, bats like the spaces between bark and a tree trunk. So a space that is narrow and dark is ideal.

Carla Brown from the National Wildlife Federation has put together her own, very well illustrated, step-by-step process for building a bat house for her home. So, rather than repeating what she has already done, I’m just going to point you to her project page for the step by step details.

Carla’s descriptions are excellent, and she writes that she had never before used a circular saw, so this is not an overly-challenging project to do. The plans she used are from Bat Conservation International’s website. The house doesn’t look like some of the commercial bat houses I’ve seen for sale. But I believe this design is more likely to attract bats to actually live in the bat house.

My seven year-old son and I are going to try to build our own bat house to put on our house this weekend following these directions. It’s a small project, requiring only a quarter sheet (2′ x 4′) of plywood, an 8′ long 1×2 board, and some miscellaneous hardware and building materials. It should be very possible to use some salvaged lumber for this if you happen to have some pieces you’d like to use.

The project requires only a couple of cuts to cut the plywood into three pieces for the house. The finished house is only a couple inches deep, but that is sufficient and cozy space for the bats. The narrow size also helps to keep other predators and animals out of the box, and keeps the bats safe.

The most unusual step of the project is probably running the circular saw in horizontal bands across the plywood to make a surface that the bats can get a grip on. Cutting rough grooves makes the plywood more like the bark that bats would expect to find. It is also important that the interior of the bat house be stained to help make it as dark as possible to appeal to the bats.

Good locations for bat houses include a southern orientation, especially in more northerly locations, and proximity to water. Sothern orientation helps the box reach the temperatures bats seek, and proximity to water makes it more likely that the insects the bats love to eat (such as mosquitoes) will be available for them. We are fortunate to have the side of the garage facing south, so it’s easy to mount the bat house at the peak of the roof to get good southern orientation. It’s less well suited for other solar projects, but it’s good for the bats. We are also quite close to the Huron River, so proximity to water is also taken care of.

Bats seek really warm nesting places, so the bat house needs to be painted or stained a dark color in order to absorb solar radiation and get as warm as possible. Bat Conservation International even has a map with guidelines on recommended colors for your bat house. Black or dark gray is usually best in northern regions.

It is unlikely that our bat house will be occupied until next year. The NWF says that bats are likely to be looking for a home in the spring, so the bat house may sit unoccupied until then. But hopefully we’ll have bats. We’ve seen bats out at nearby parks, so hopefully they’ll find our bat box and move in.