How to Build a Bat House for Your Yard

Bugs Beware, Here Come the Bats!

Despite their scary reputation, bats are a critical and harmless part of a healthy environment. They help keep bug populations under control by eating tons of insects every night—not bad for a tiny mammal weighing less than a 1/2 ounce. Bats are the only mammal that truly flies, and are well-known for putting on a great show with high-speed twists and turns, using an echolocation system so advanced we have yet to fully understand how it works. Some species are also important pollinators, and in the tropics, bats are critical to seed dispersal and forest regeneration.

Still not convinced? Here are a few more facts about bats:

Bats can eat close to their own weight in bugs every night—more than 1,000 mosquitoes in an hour. Bats also consume huge quantities of agricultural pests, reducing the need for toxic pesticides.

Bat sonar is more sophisticated and efficient than comparable human technology. Bats in flight send out anywhere from 10 to over 200 ultrasonic calls per second, and almost instantly translate the sound waves that echo back into images so precise that they can detect a single human hair in total darkness while flying at full speed. And far from being blind, most have good eyesight.

Bats never attack humans, but they enjoy the tasty mosquitoes and gnats swirling around our heads, and will occasionally swoop close to get one.

Contrary to myth, bats almost never cause rabies in humans. For the entire U.S., bats cause only 1.3 cases of human rabies each year.

There are no vampire bats in the U.S., and they don’t like human blood anyway—farm animals taste better.

Most bats return to the same nesting and hibernating sites year after year, and have been known to live more than 30 years.

Female bats average only one birth a year, and popu- lations in various parts of the country have declined dra- matically. However, bats, like many birds, are quite willing to live in man-made houses, so long as they’re warm and dry and have someplace to hang from. You can buy bat houses for $35 to $180, or better yet, build your own (see the step-by-step instructions on pages 42-43). A simple three-chambered house big enough for a bat nursery takes less than a day to build and finish, and even the Taj Mahal of bat houses will only take a weekend.

“Installing bat houses helps replace lost natural habitat, and is one way the average person can make a real difference in conservation.” — Mark Kiser Bat Conservation International

First, Find the Right Location

Bats need plenty of warmth—roughly 10 hours of direct sunlight in cold climates, down to 6 hours in desert areas. They prefer a high location for protection from predators, at least 12 feet up on a post or the side of a house in an area clear of tree branches. You can also attach bat houses to trees, so long as the bat house gets enough direct sunlight and isn’t surrounded by branches.

Bats like to be within a 1/4 mile of water (or at least a backyard pond), and prefer areas with plenty of natural vegetation and nearby farmland. However, one of the largest bat roosts in the country is under a busy bridge in the middle of Austin, Texas.

Build a Basic Bat House

Lay out the two partitions (A) and the back panel (B) on a sheet of 3/8-inch exterior plywood (Photo 1). A table saw makes the next step easy, but if you don’t have one, a circular saw works just fine. Draw a line every 1/2 inch across the panels, going with the grain of the plywood, then cut a shallow kerf 1/16 inch deep at each line. This is a little tedious, but the whole process of marking and cutting will only take 30 to 45 minutes (honestly, I timed it). Cut the panels to the sizes shown in the Cutting List.

Cut the 1×6 sides (J) (roof slope is 22-1/2 degrees), the 1×8 roof (H), the tongue and groove front panels (F), and

the spacers (C and D). Cut the vent slot for the front panel (Photo 3). If you’re making a double pole-mounted house (Fig. B), or if you live in a climate where average summer daytime temperatures exceed 95°, cut an additional vent slot in the back panel (B) (Photo 1).

For rot resistance, and to make the interior homier for darkness-loving bats, stain the inside faces of all the pieces before assembly. Use water-based stain for the interior be- cause primer and paint tend to fill the saw kerfs.

Set the rear spacers (C) 3/8 inch from the back edge of the sides (J), and attach with four predrilled 1-1/4-inch screws per side. Set the two sides upright on a flat surface and set the back panel (B) on the spacers. Make the panel flush with the top edge of the sides (J). Predrill and screw four 1-inch screws along each edge into the spacers.

Flip the house over and attach the first partition (A), keeping the panel 1/2 inch down from the top edge to al- low for ventilation in the house. Add the next set of spac- ers (D), screwing them into the sides, and then attach the last partition (A) and the final set of spacers (D) (Photo 2).

CUT SAW KERFS

1. Cut saw kerfs 1/16-inch deep on the good side of the plywood, apply a coat of dark stain, then cut it for back (B) and two partitions (A).

PREDRILL AND SCREW

2. Screw the 3/4-inch spacers to the sides, and screw the back and partitions to the spacers. Leave a 1/2- inch gap at the top for air flow.

ADD THE FRONT PANEL

3. Slide the 1×8 tongue and groove pieces (F and G) into place, and attach with one predrilled screw to spacer (D). Finally, cut a 22-1/2-degree angle on the 3/4-inch trim pieces (E) and screw them into the sides, flush with the top. Then center the 1×8 roof, predrill and attach with 1-5/8- inch screws.

ATTACH THE BAT HOUSE

4. Install the bat house on the post with four 1-5/8-inch screws at each end, and then place the post in the hole and plumb and brace it with 1x4s until the concrete sets.

Caulk all corners with a paintable latex caulk, and apply a water-based exterior stain or paint to all exposed wood (see below for color recommendations). The bat house is left open at the bottom to reduce cleaning and mainte- nance, but also because it makes the bat house less attractive to nest-building wasps.

Installation

Screw two 1x6s (K)to the solid wood sides on the back of the bat house (see Fig. A). Place the lower 1×6 just above the rear vent (if you have one). Bend the metal roof flashing back over the upper 1×6. Caulk the top of the lower 1×6. Screw a vertical 1×4 (L) to the center of the two 1x6s, extending it 4 inches above and below the house. Attach the bat house to a 16-foot-long 4×4, then tip the post into a 3-foot-deep hole and fill with concrete (Photo 4).

The Right Color Bat House for Your Climate

Darker colors absorb more heat and work better in cold climates, while the lighter colors reflect more heat. Here are some color recommendations for bat houses in your region:

USDA Climate Zones 2, 3, 4 (upper third of the U.S. and Canada and Pacific Coast): black walls and dark roof. l Zones 5 and 6 (central U.S.): medium dark walls and roof.

Upgrading to a Deluxe Bat House

Back-to-back bat houses have proven to be very successful, often attracting hundreds of bats. Install two basic bat houses (with back panels saw-kerfed) on two posts at least 12 feet in the air. Cut 3/4-inch by 6-inch slots in the backs of both houses and leave a 3/4-inch gap between the houses, so that bats can travel back and forth from warmer to cooler areas. Join the houses with horizontal 1x4s (Fig. B). Screw vertical 1x4s to the horizontal 1x4s, extending them 4 inches above and below the houses. Attach the houses to the posts, and bend a piece of flashing over the tops of the houses to form a roof. Add two 1×4 cross pieces between the 4x4s, 6 feet up from the bottom for stability, then set the posts in 3-foot-deep holes and fill with concrete. Plumb and brace the poles until the concrete sets.

How to Prevent a Bat Problem

PDF Links:

Figure A

Figure B

The Bats Are Living in the Wrong House!

If you’ve got bats in your attic, locate the hole the bats use to get in by watching at twilight. Tape a large piece of 1/16-inch screening around the hole, but leave it open and loose at the bottom so bats can crawl out, but not in. (Do this before May or after August to avoid trapping babies inside your attic.)

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