A bat house

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One role that has huge benefits for our species is that of primary consumers of insects, including mosquitos. An individual bat can consume hundreds of mosquitoes in an hour. Unfortunately, these small flying mammals are in jeopardy for many reasons. Loss of habitat is one threat faced by bats. The use of pesticides and other chemicals along with nursing colonies being exterminated in houses and other buildings are two more serious threats to the health of bat populations. Wind turbines also kill numerous bats.

White-Nose Syndrome


Another threat to bats, this fungal disease has resulted in the deaths of millions of bats in eastern North America in the last decade. The fungus, which is from Eurasia and was accidentally brought to North America by humans, can survive on people’s boots, clothing and equipment.

The fungus can grow on the muzzles and wings of an infected bat during hibernation. It causes damage to the affected areas. It also results in bats behaving abnormally, including waking more often during hibernation, which uses up vital fat reserves. Some hibernating bat colonies with the fungus result in 100% of the bats dying.

Child building a bat house

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Building a Bat House


Aside from keeping your property in a relatively natural state, avoiding the use of pesticides and other harmful chemicals and keeping your house (and other structures) in good repair (bats can access openings as small as 1cm in diameter), you can assist bats by building a home or two for them. About 30 years ago, I was given instructions on how to make a bat house. Not being as talented at building things as my wife Lynn, I gave the plans to her. Lynn constructed a beautiful bat house that has been home to at least one bat every year since. The bat house is occupied from spring until fall. Lynn has made two more bat boxes – one with the help of our children. Here are the instructions for the bat home we provide for our bat neighbors in exchange for some natural bug control!

Materials List


  • (1) 1" x 6" x 8' Sheeting Pine (rough sawn on one side)
  • (1) Box of 1-1/4" wood screws
  • (2) 2" screws to attach bat box to building/ post
  • (1) small hinge (2" x 1-3/8")
  • (1) turn button

Cut List:


  • (1) 5-1/2" x 14" (back)
  • (3) 5-1/2" x 12" (sides and front)
  • (1) 5-1/2" x 9" (middle)
  • (1) 5-1/2" x 7" (top)
  • (1) 5-1/2" x 1-3/4" (bottom trap door)


Note: Dimensions are approximate, as sheeting pine is dressed on one side and dimensions are slightly smaller.

Interior of bat house

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Instructions


  1. Using a 1" x 6" x 8' piece of untreated sheeting pine, cut the board into the pieces specified above except for the bottom trap door. Sheeting pine is used, as it has rough-sawn wood on one side. This side should go on the inside of the bat box so that bats can grip onto the wood.

  2. For the 5-1/2" x 9" middle interior piece, create horizontal scratches or grooves on the smooth side of the board about 13mm apart and 1mm deep using a table saw to give the bats something to grip onto. Similar grooves can also be created on the rough-cut side of the back board.

  3. Align the tops of the two 5-1/2" x 12" side boards with the 5-1/2" x 14" back board. Using 1-1/4" wood screws, attach the side pieces to the back piece, ensuring the rough-cut sides of the boards are on the interior of the bat house.

  4. Screw the 5-1/2" x 9" board that divides the inside of the bat box into two compartments to the side boards, again aligning the top of the middle board with the top of the sides. The 5-1/2" x 12" front board can now be screwed to the front edges of the side boards. Next, screw the 5-1/2" x 7" board onto the top of the bat box.
A completed bat house

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  1. You are now ready to cut and attach the hinged bottom trap-door board (approximately 5-1/2" x 1-3/4"). Measure the opening for the trap door and adjust the size to the true opening size. Cut the trap-door board. Using a hinge, attach the 5-1/2" side of the bottom trap door to the bottom of the inside of the front of the bat house, ensuring the rough-cut side is inside.

  2. Attach a "turn button" to the bottom edge of the bat house to keep the trap door in the closed position. You can clean any bat excrement that has accumulated in the bat house by turning the button, allowing the bottom of the house to open. For safety reasons, wear an appropriately rated mask and clean the house when bats aren’t in it (possibly late fall or winter if they have travelled to winter roosts) as rabies and histoplasmosis (a fungal disease from bat droppings) are two health concerns associated with bats.

  3. Secure the bat box to its permanent location using two screws of appropriate length through the 5-1/2" x 14" back board a couple of inches from the bottom of the bat box.



Note: We don’t usually use any finish or paint on the exterior, as natural pine will weather dark grey to absorb heat. The inside is also untreated. The exterior of our first bat house was stained to match the house exterior it is mounted on.

Construction diagram for bat house
Locating the bat house

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Locating the Bat House


Bat houses can be mounted on buildings or poles and should be at least four metres off the ground – preferably higher. Locating the houses in trees isn’t ideal, as this makes the bats more vulnerable to predators. Bat houses located reasonably close to a water source, such as a stream, pond or lake, have a better chance of attracting bats. Bat houses should be located where they receive lots of direct sunlight, and the area around the house should be clear so that the bats can easily enter and exit the house. Do not locate a bat house near bright lights.

A Final Word


While I haven’t seen any of our lodgers up close, the ones that have recently resided in the first bat house Lynn made could be the original tenants, as bats can live for more than 30 years. With serious threats facing bats, I breathe a sigh of relief each spring when it is confirmed that our lodger, or lodgers, have returned to their home for another year.

How to Build a Bat House

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You can get more information on bats and how you can help them, including building and installing bat houses, at the Bat Conservation International website at the links below.

  • http://www.batcon.org/

  • http://www.batcon.org/resources/getting-involved/bat-houses

  • http://www.batcon.org/images/InstallingYourBatHouse_Building.pdf

Text by N. Glenn Perrett

Photographs by Lynn and Glenn Perrett

N. Glenn Perrett and his family live in Mulmur, Ontario, on a property that includes a diversity of animals – including bats. His book on the national parks of southern Ontario was published by Fitzhenry & Whiteside in summer 2019.

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