Choose a single-chamber house for a wall, or two houses back to back for a pair of poles, then the height and width. The plan gives the shopping list, the cuts on the plywood sheet and the furring strip, and each step with a drawing.
Choose a single-chamber house for a wall, or two houses back to back for a pair of poles, then the height and width. The plan gives the shopping list, the cuts on the plywood sheet and the furring strip, and each step with a drawing.
Reviewed by FigureYard editorial teamUpdated October 9, 20269 sources
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Item
Qty
Price each
Total
1x2 furring strip, pine, 8 ft long
1 board
–
1x4 board, pine or cedar, 8 ft long
1 board
–
1/2 in exterior plywood (AC, BC or T1-11), 4 ft × 8 ft sheet
1 sheet
–
Exterior-grade screws, 1 in34 needed plus 5 spares
39 screws
–
Exterior screws, 3 in, for the wall
4 screws
–
Paintable latex caulk
1 tube
–
Dark water-based stain, exterior grade, for the inside
1 pint
–
Water-based exterior primer
1 pint
–
Flat water-based exterior paint or stain, in the color for your climate
1 quart
–
Total for the items you priced
–
Cut list
Part
What it is
Lumber
Size
Cut
A
Backthe bottom 4 1/2 in below the front is the landing area
1/2 in exterior plywood (AC, BC or T1-11)
26 1/2 × 24 in
1
B
Front, upper
1/2 in exterior plywood (AC, BC or T1-11)
16 1/2 × 24 in
1
C
Front, lower
1/2 in exterior plywood (AC, BC or T1-11)
5 × 24 in
1
D
Top spacer
1x2 furring strip, pine
24 in
1
E
Side spacers
1x2 furring strip, pine
20 1/2 in
2
F
Roof
1x4 board, pine or cedar
28 in
1
Where to cut each board
Each bar is one board you buy, drawn to scale. Measure from the left end, cut, then measure the next piece from the fresh cut; the saw blade takes about 1/8 in each time. Hatched ends are offcuts.
1x2 furring strip, pine
1x4 board, pine or cedar
1/2 in exterior plywood (AC, BC or T1-11), sheet 1 of 1
Tools
Tape measure, pencil and a straightedge
Circular saw or table saw, and a handsaw for the grooves
Drill/driver and a pilot bit
Caulking gun and paintbrushes
Safety glasses and hearing protection
Step by step
Cut the pieces
Cut the back A, the upper front B and the lower front C from the plywood, all 24 in wide, following the sheet diagram. Keep the good face of the plywood for the outside.
Cut the furring strip into the top spacer D, 24 in long, and two side spacers E, 20 1/2 in long. Cut the roof F from the 1x4, 28 in long.
Roughen the inside
Bats cling to the wood, so the inside of the back and the landing area need grip. Saw shallow grooves across the back A, 1/4 in to 1/2 in apart and 1/32 in to 1/16 in deep, all the way down to the bottom edge. Cut no deeper, or the plywood weakens.
Brush 2 coats of dark water-based stain on the inside faces of the back and the front pieces and let them dry. Do not use paint inside: it fills the grooves.
Screw the spacers to the back
Run a bead of caulk where each spacer goes, then screw the top spacer D along the top of the back and the side spacers E down each edge, below it. The spacers leave the bottom open: that is the entrance.
Screw: caulk the joint first, drill a pilot hole, then drive the screw
Put the front on
Caulk the spacers, then screw the upper front B on, flush with the top. Leave a 1/2 in gap below it and screw on the lower front C: the gap is the vent that keeps the house from overheating.
Caulk every outside joint so the chamber is dry and free of drafts.
Roof and paint
Screw the roof F on top, flush with the back, so it overhangs the front and 2 in past each side. Caulk the joint along the top.
Paint or stain the outside 3 times, primer first, in the color for your climate (see below). Cover the roof with shingles or galvanized metal for a longer life, if you like.
Put it up
Mount the house on a wall of the building, south or east sides being usually best, 12 ft or more off the ground and better 15 ft to 20 ft. Drive two 3 in screws through the front, the top spacer and the back near the top, and two through the landing area, into the wall framing.
Keep it clear of branches, lights and anything a predator could climb, and leave the space below the entrance open so the bats can drop out to fly.
Good to know
Use exterior plywood and untreated wood: pressure-treated wood may be toxic to bats. Screws hold better than nails.
Check it each winter, when the bats are gone: re-caulk and repaint as needed.
In very cold places, BCI leaves out the vent and makes the front one piece; elsewhere the vent keeps the bats from overheating.
The design is Bat Conservation International's single-chamber bat house, the plan in its Bat House Builder's Handbook, and every house meets BCI's criteria for houses that bats actually use: a roost chamber big enough, spaced just right, rough enough to cling to, vented, and with a landing area below the entrance.
How to use this calculator
Choose the design. A single house goes on the wall of a building, which keeps it warmer at night; a back-to-back pair goes between two posts and makes three chambers.
Choose the height. The tall house gives the bats more room to move up or down as the day warms and cools.
Choose the width and how many to build. Several houses share the plywood sheet and the strips.
Follow the steps in order: cut, roughen and stain the inside, screw on the spacers and the front, add the roof, paint, and put it up.
Worked examples
A single house for a wall
Design: Single chamber, on a wall
Bat house
24 × 26.5 in
Roost chamber
21 × 20.5 in, 0.75 in deep
Landing area
4.5 in
Chambers
1
Boards to buy
2
A tall single house
Design: Single chamber, on a wall · Height: Tall (more room for the bats to move up and down)
Bat house
24 × 51 in
Roost chamber
21 × 44 in, 0.75 in deep
Landing area
5.5 in
Chambers
1
Boards to buy
3
A back-to-back pair on posts
Design: Two houses back to back, on poles
Each house in the pair
24 × 26.5 in
Roost chamber
21 × 20.5 in, 0.75 in deep
Landing area
4.5 in
Chambers in each pair
3
Boards to buy
3
A wider house for a bigger colony
Design: Single chamber, on a wall · Width: 30 in
Bat house
30 × 26.5 in
Roost chamber
27 × 20.5 in, 0.75 in deep
Landing area
4.5 in
Chambers
1
Boards to buy
2
Three houses for a barn and a garage
Design: Single chamber, on a wall · How many to build: 3
Bat house
24 × 26.5 in
Roost chamber
21 × 20.5 in, 0.75 in deep
Landing area
4.5 in
Chambers
1
Boards to buy
4
What makes a bat house work
A roost chamber at least 14 inches wide and 20 inches tall; taller and wider is better.
The chamber 0.75 to 1 inches deep, front to back: the spacers set it.
A landing area of 3 to 6 inches below the entrance, where bats land and climb in.
Rough surfaces to cling to: shallow grooves sawn across the back and the landing area. BCI no longer suggests plastic mesh, and metal screen or hardware cloth can injure bats.
A vent gap of 0.5 inch across the front, so the house does not overheat on hot days.
Caulked seams, dark stain inside and paint outside, so the house stays dry, dark and draft-free for years.
Where to put a bat house
Mount it at least 12 ft off the ground, and better 15 to 20 ft, on a building or a pole rather than a tree, where predators reach it more easily and the shade keeps it cool. Keep it 20 to 30 ft from branches and other obstacles where you can.
Bats need warmth: give the house at least 6 hours of direct sun a day, and 10 hours or more where July highs average 80 °F or less. Houses within 0.25 mile of a stream, river or lake do best.
What color to paint it
The color sets how warm the house gets. Paint it black where the average July high is below 85 °F, dark brown or dark gray up to 95 °F, a medium color up to 100 °F, and white or a light color where it is hotter still.
Use water-based exterior paint or stain, primer first, and 3 coats in all. Inside, use only dark stain: paint fills the grooves the bats cling to.
Common questions
What is the best design for a bat box?
One with a tall, wide roost chamber spaced 0.75 to 1 inches deep, rough inside, with a landing area below the entrance and a vent. Bigger houses do better: in BCI's surveys, 36 percent of small single-chamber houses were occupied, against 54 percent of medium ones, the size of a back-to-back pair. A single-chamber house belongs on the wall of a building, which evens out the swings in temperature.
How high should a bat house be?
At least 12 ft off the ground, and better 15 to 20 ft, with open space below it so the bats can drop out and fly.
Which direction should a bat house face?
Where it gets the most sun in your climate: at least 6 hours of direct sun a day. For a single house on a building, the south or east side is usually best.
Will a bat house attract bats?
Often, if it is built and placed right, though not at once. In BCI's surveys, the houses that bats moved into took 9 months on average, and 89 percent of them were in use within two years. Sun, height and nearby water matter most; if a house stays empty for two years, try a sunnier or warmer spot.
Should I paint my bat house?
The outside, yes: 3 coats of water-based paint or stain, primer first, in a color that suits your summers. The inside gets only dark stain, never paint.
Are there downsides to having a bat house?
Guano collects under the house, so do not put it over a door, a window or a patio. Never handle bats with bare hands: a bat on the ground may be sick. Otherwise bats are quiet neighbors that eat a lot of night-flying insects.
The design is Bat Conservation International's single-chamber bat house, the plan in its Bat House Builder's Handbook, and every house meets BCI's criteria for houses that bats actually use: a roost chamber big enough, spaced just right, rough enough to cling to, vented, and with a landing area below the entrance.
How to use this calculator
Choose the design. A single house goes on the wall of a building, which keeps it warmer at night; a back-to-back pair goes between two posts and makes three chambers.
Choose the height. The tall house gives the bats more room to move up or down as the day warms and cools.
Choose the width and how many to build. Several houses share the plywood sheet and the strips.
Follow the steps in order: cut, roughen and stain the inside, screw on the spacers and the front, add the roof, paint, and put it up.
Worked examples
A single house for a wall
Design: Single chamber, on a wall
Bat house
60.96 × 67.31 cm
Roost chamber
53.34 × 52.07 cm, 19.05 mm deep
Landing area
11.43 cm
Chambers
1
Boards to buy
2
A tall single house
Design: Single chamber, on a wall · Height: Tall (more room for the bats to move up and down)
Bat house
60.96 × 130 cm
Roost chamber
53.34 × 112 cm, 19.05 mm deep
Landing area
13.97 cm
Chambers
1
Boards to buy
3
A back-to-back pair on posts
Design: Two houses back to back, on poles
Each house in the pair
60.96 × 67.31 cm
Roost chamber
53.34 × 52.07 cm, 19.05 mm deep
Landing area
11.43 cm
Chambers in each pair
3
Boards to buy
3
A wider house for a bigger colony
Design: Single chamber, on a wall · Width: 76 cm (30 in)
Bat house
76.2 × 67.31 cm
Roost chamber
68.58 × 52.07 cm, 19.05 mm deep
Landing area
11.43 cm
Chambers
1
Boards to buy
2
Three houses for a barn and a garage
Design: Single chamber, on a wall · How many to build: 3
Bat house
60.96 × 67.31 cm
Roost chamber
53.34 × 52.07 cm, 19.05 mm deep
Landing area
11.43 cm
Chambers
1
Boards to buy
4
What makes a bat house work
A roost chamber at least 36 cm wide and 51 cm tall; taller and wider is better.
The chamber 1.9 to 2.5 cm deep, front to back: the spacers set it.
A landing area of 7.6 to 15 cm below the entrance, where bats land and climb in.
Rough surfaces to cling to: shallow grooves sawn across the back and the landing area. BCI no longer suggests plastic mesh, and metal screen or hardware cloth can injure bats.
A vent gap of 1.3 cm across the front, so the house does not overheat on hot days.
Caulked seams, dark stain inside and paint outside, so the house stays dry, dark and draft-free for years.
Where to put a bat house
Mount it at least 3.7 m off the ground, and better 4.6 to 6.1 m, on a building or a pole rather than a tree, where predators reach it more easily and the shade keeps it cool. Keep it 6.1 to 9.1 m from branches and other obstacles where you can.
Bats need warmth: give the house at least 6 hours of direct sun a day, and 10 hours or more where July highs average 27 °C or less. Houses within 0.4 km of a stream, river or lake do best.
What color to paint it
The color sets how warm the house gets. Paint it black where the average July high is below 29 °C, dark brown or dark gray up to 35 °C, a medium color up to 38 °C, and white or a light color where it is hotter still.
Use water-based exterior paint or stain, primer first, and 3 coats in all. Inside, use only dark stain: paint fills the grooves the bats cling to.
Common questions
What is the best design for a bat box?
One with a tall, wide roost chamber spaced 1.9 to 2.5 cm deep, rough inside, with a landing area below the entrance and a vent. Bigger houses do better: in BCI's surveys, 36 percent of small single-chamber houses were occupied, against 54 percent of medium ones, the size of a back-to-back pair. A single-chamber house belongs on the wall of a building, which evens out the swings in temperature.
How high should a bat house be?
At least 3.7 m off the ground, and better 4.6 to 6.1 m, with open space below it so the bats can drop out and fly.
Which direction should a bat house face?
Where it gets the most sun in your climate: at least 6 hours of direct sun a day. For a single house on a building, the south or east side is usually best.
Will a bat house attract bats?
Often, if it is built and placed right, though not at once. In BCI's surveys, the houses that bats moved into took 9 months on average, and 89 percent of them were in use within two years. Sun, height and nearby water matter most; if a house stays empty for two years, try a sunnier or warmer spot.
Should I paint my bat house?
The outside, yes: 3 coats of water-based paint or stain, primer first, in a color that suits your summers. The inside gets only dark stain, never paint.
Are there downsides to having a bat house?
Guano collects under the house, so do not put it over a door, a window or a patio. Never handle bats with bare hands: a bat on the ground may be sick. Otherwise bats are quiet neighbors that eat a lot of night-flying insects.