How to Build a Birdhouse That Attracts Bluebirds and Wrens

Dimensions for Three Target Species

Each cavity-nesting species has specific size preferences. A birdhouse built for a bluebird has different proportions than one built for a wren. The table below covers the three most common backyard cavity nesters in North America.

Eastern Bluebird

Floor size: 5x5 inches. Interior depth (floor to bottom of entrance hole): 6 to 8 inches. Entrance hole diameter: 1.5 inches. Entrance hole height from floor: 6 inches. Box height above ground when mounted: 4 to 6 feet. Bluebirds prefer open habitats: meadows, large lawns, pastures, and golf course edges. They avoid dense woods and shaded areas. Mount the box facing east or southeast so the morning sun warms the interior, which helps incubating females conserve energy.

House Wren

Floor size: 4x4 inches. Interior depth: 4 to 6 inches. Entrance hole diameter: 1.125 inches. Entrance hole height from floor: 5 inches. Box height above ground: 5 to 10 feet. Wrens tolerate partial shade and are comfortable near shrubs, hedgerows, and woodland edges. The smaller entrance hole (1.125 inches) excludes bluebirds and house sparrows while allowing wrens to enter. Wrens are aggressive nesters and will fill multiple boxes with twigs even if they only use one. If you want bluebirds, do not place wren boxes within 50 feet of bluebird boxes.

Black-Capped Chickadee

Floor size: 4x4 inches. Interior depth: 6 to 8 inches. Entrance hole diameter: 1.125 inches. Entrance hole height from floor: 6 inches. Box height above ground: 4 to 8 feet. Chickadees prefer forested or semi-wooded areas with mature trees. They are comfortable in backyards with large shade trees. The 1.125-inch hole excludes house sparrows (which need at least 1.25 inches) while allowing chickadees to enter.

Choosing the Right Wood

Use untreated 1x6 cedar or redwood boards. Cedar costs $8 to $12 per 6-foot board at Home Depot. Redwood costs $12 to $18 per board. Both species resist rot and insect damage naturally, without chemical treatment. Treated lumber (the green-tinted boards at the hardware store) contains copper azole or alkaline copper quaternary, which are toxic to birds if ingested. Birds chew on the interior walls of nest boxes, and treated wood can poison nestlings.

Pine and spruce work but rot within 3 to 5 years in wet climates. If you use pine ($5 per 6-foot board), apply two coats of raw linseed oil ($7 per quart) to the exterior surfaces only. Linseed oil is a natural wood preservative that is non-toxic to birds once fully cured (allow 2 weeks of drying time before mounting). Do not apply linseed oil to the interior walls; birds need rough wood surfaces inside the box to grip when climbing out.

Avoid plywood. The glues in plywood off-gas formaldehyde, which is harmful to birds in an enclosed space. Exterior-grade plywood has lower formaldehyde emissions than interior-grade, but solid wood is still the safer choice. One 6-foot 1x6 cedar board ($10) provides enough material for one complete birdhouse with some waste.

Cut List for a Bluebird House

This cut list produces a standard bluebird house with a 1.5-inch entrance hole. The actual dimensions of a 1x6 board are 0.75 inches thick by 5.5 inches wide. All cuts are made from a single 6-foot 1x6 cedar board.

Back panel: 5.5 inches wide by 12 inches long. This is the full width of the board. Front panel: 5.5 inches wide by 9 inches long. The front is shorter than the back, which creates a slope for the roof to shed water. Roof: 5.5 inches wide by 7 inches long. The roof overhangs the front by 1 inch and the sides by 0.25 inch on each side. Two side panels: 4 inches wide by 9 inches tall on the front edge and 12 inches tall on the back edge. The angled top follows the roof slope. Floor: 4 inches wide by 4 inches deep. Cut from the remaining board width by ripping to 4 inches on a table saw, or use a jigsaw.

Mark all cuts with a pencil and square before cutting. A circular saw with a fine-tooth blade (40 teeth or more) produces clean cuts in cedar without splintering. Sand all cut edges lightly with 120-grit sandpaper to remove splinters, but leave the interior faces rough. Rough interior surfaces help fledglings grip the wood when they climb to the entrance hole to leave the nest.

Drilling the Entrance Hole

The entrance hole goes in the front panel, centered horizontally, with the center of the hole positioned 6 inches above the top of the floor. For a bluebird house, use a 1.5-inch spade bit ($4) or Forstner bit ($8). For a wren or chickadee house, use a 1.125-inch bit.

Mark the hole center with a pencil. Drill from the exterior face of the front panel inward. Spade bits tend to splinter the wood on the exit side. To prevent splintering, clamp a scrap piece of wood behind the front panel and drill through both layers. The scrap absorbs the splintering and keeps the interior face of the front panel clean.

Do not add a perch below the entrance hole. Perches help predators (raccoons, cats, and larger birds) access the nest. Cavity-nesting birds do not need perches because their claws grip the rough wood interior directly. Perches are a feature of decorative birdhouses sold at craft stores, not of functional nest boxes designed for bird conservation.

Assembling the Birdhouse

Step 1: Attach the Floor

Position the floor between the two side panels, 0.25 inches up from the bottom edges of the sides. The gap at the bottom provides drainage. Drill four pilot holes (1/16-inch bit) through each side panel into the floor edges. Drive 1.5-inch exterior screws through the pilot holes. Predrilling prevents the cedar from splitting, which is a common problem with thin boards and screws placed near the edge.

Step 2: Attach the Back Panel

Position the back panel against the rear edges of the side panels. The back panel extends 1.5 inches above the top of the side panels and 1.5 inches below the bottom. The lower extension provides a mounting surface for screws or nails when you hang the box. The upper extension provides a gap for ventilation. Drill pilot holes and drive 1.5-inch exterior screws through the back panel into the side panels, two screws per side.

Step 3: Attach the Front Panel

The front panel pivots on two screws at the top, acting as a cleaning door. Position the front panel against the front edges of the side panels. Drill a single pilot hole near the top of each side panel, 1 inch below the top edge. Drive one 1.5-inch exterior screw through each side panel into the front panel. These two pivot screws allow the front panel to swing open like a door for cleaning.

At the bottom of the front panel, drill a single hole on each side and drive a screw partway in to act as a latch. Alternatively, use a 1-inch brass screw at the bottom of one side as a lock screw; tighten it to secure the front panel for nesting season, and loosen it to swing the panel open for cleaning between broods.

Step 4: Attach the Roof

Position the roof on top of the assembled box, centered so it overhangs the front by 1 inch and the sides by 0.25 inch. The overhang protects the entrance hole from rain. Drill two pilot holes through the roof into the back panel extension. Drive 1.5-inch screws. Do not screw the roof to the front panel; the front panel needs to swing open independently.

Step 5: Drill Ventilation and Drainage Holes

Drill four 1/4-inch ventilation holes near the top of each side panel, just below the roof line. These holes allow hot air to escape in summer. Interior temperatures in a poorly ventilated birdhouse can reach 120 degrees Fahrenheit on a 90-degree day, which is lethal to nestlings. Without ventilation holes, the box becomes an oven.

Drill four 1/4-inch drainage holes in the floor near the corners. Rainwater that enters through the entrance hole or ventilation holes needs a way out. Drainage holes also allow any moisture from wet nesting material to evaporate. The 0.25-inch gap between the floor and the side walls provides additional drainage.

Where and How to Mount the Box

Mount the birdhouse on a smooth metal pole or a 4x4 wooden post. A 5-foot section of 0.5-inch EMT conduit ($6 at Home Depot) with a flange ($3) bolted to the bottom of the birdhouse works well. Metal poles are harder for raccoons and snakes to climb than wooden posts. If you use a wooden post, wrap a 6-inch-wide metal predator baffle ($12 to $18) around the post 4 feet above the ground. The baffle prevents raccoons, snakes, and cats from reaching the nest.

Face the entrance hole toward the east or southeast. Morning sun warms the box after cool nights, which helps females maintain the 96 to 100 degree Fahrenheit incubation temperature required for eggs. Avoid facing the hole west or southwest, where afternoon sun overheats the box in summer.

Mount the box at the species-specific height listed in the dimensions section. For bluebirds, that is 4 to 6 feet above the ground. Place the box at least 100 feet from brush piles, thickets, or buildings where house sparrows roost. House sparrows are the primary competitor for bluebird nest boxes and will aggressively drive bluebirds away, destroy eggs, and kill nestlings.

Space multiple boxes at least 100 feet apart for bluebirds (they are territorial and defend feeding areas of roughly 2 to 3 acres). Wren boxes can be placed 25 to 50 feet apart since wrens defend smaller territories.

Monitoring and Cleaning the Nest Box

Check the box once a week during nesting season (March through August in most of the United States). Open the front panel and quickly inspect the nest contents. Bluebird nests are neat cups of woven grass or pine needles, typically 2 to 3 inches deep. House sparrow nests are messy domes of grass, weeds, paper, and garbage that fill the entire box. If you find a house sparrow nest, remove it and discard the contents. House sparrows are not protected by federal law and can be legally removed from nest boxes.

Bluebird eggs are pale blue, typically 4 to 5 per clutch. Incubation takes 13 to 14 days. Nestlings fledge 16 to 21 days after hatching. Do not open the box after the nestlings are 12 days old, as they may fledge prematurely if startled. Once the brood has fledged (you will see an empty nest with no activity for 2 days), open the front panel, scrape out the old nest with a putty knife, and brush the interior with a stiff brush. Do not reuse old nests; they harbor mites and parasites that infect the next brood.

Leave the box up through winter. Bluebirds roost in nest boxes during cold weather, and several birds may huddle together in a single box for warmth. Clean the box one final time in late February before the spring nesting season begins.

Troubleshooting: Why Birds Are Not Using the Box

House Sparrows Keep Taking Over

House sparrows are the number one reason bluebird boxes fail. If sparrows repeatedly build nests in your box, try a sparrow spooker: attach a 6-inch strip of Mylar ribbon ($2 for a roll) to the top of the box so it hangs over the entrance hole. The fluttering ribbon deters sparrows but does not bother bluebirds. Alternatively, trap and humanely euthanize house sparrows using an inbox trap ($15 from the North American Bluebird Society). House sparrows are an invasive species and are not protected by the Migratory Bird Treaty Act.

Ants Invading the Nest

Apply a thin coat of petroleum jelly to the pole or post below the box. Ants cannot cross the greasy surface. Reapply after heavy rain. Do not use insecticide inside or near the box; it is toxic to birds and nestlings.

Blowflies in the Nest

Blowfly larvae are small brown grubs that live in the nesting material and feed on nestling blood at night. Check for larvae by lifting the nest slightly with a putty knife during weekly inspections. If you find more than 10 larvae, replace the nest with a similar amount of dry grass. A hardware cloth screen ($3, cut to 4x4 inches) placed below the nest allows larvae to fall through while keeping the nest intact.

The Box Overheats

If the box receives direct afternoon sun, the interior temperature can exceed 110 degrees Fahrenheit. Either relocate the box to a shadier spot or add a second set of ventilation holes on the back panel near the top. Painting the roof white with exterior latex paint ($8 per gallon) reflects sunlight and reduces interior temperature by 10 to 15 degrees.

Material Cost for One Birdhouse

One 6-foot 1x6 cedar board: $10. One box of 1.5-inch exterior screws: $6 (enough for 8 to 10 birdhouses). One 1.5-inch spade bit: $4 (reusable). One 1/4-inch drill bit: $2 (you may already own this). Total for one birdhouse: $12 to $14. If you already own screws and drill bits, the cost is just the cedar board. Building four birdhouses from a single 6-foot board costs $10 total in wood, or $2.50 per birdhouse.

Construction time is roughly 45 minutes per birdhouse once you have made the first one and established a workflow. The first birdhouse takes about 90 minutes including measuring, cutting, and assembly.