How to Build a Swallow Bird House for Barn and Tree Swallows

Building a swallow bird house is one of the most rewarding backyard projects you can tackle, but only if you build the right kind for the right species. Get the design wrong and you will have a beautifully crafted box that no swallow ever touches. Get it right and you could have a pair nesting just a few feet from your garden every spring. Here is exactly what you need to know to build and install a swallow house that birds will actually use.

Barn swallow vs. tree swallow: which one actually uses a bird house?

This is the first thing to sort out, because it changes your entire build plan. Tree swallows are true cavity nesters, which means they will readily move into a purpose-built nest box with an entrance hole, just like a chickadee or bluebird would. Barn swallows, on the other hand, build open mud cup nests on ledges, beams, and sheltered overhangs. Texas Parks and Wildlife puts it plainly: nest boxes do not work for barn swallows the way they do for tree swallows. Barn swallows are not looking for a hole in a box; they want a platform or a sheltered shelf under a structure.

So if you searched for a barn swallow bird house, what you actually want to build is a nest shelf or cone attached to a wall, eave, or outbuilding. If you searched for a tree swallow bird house, you want a cavity-style nest box with a specific entrance hole. Both are doable DIY projects, but they are fundamentally different builds. This guide covers the tree swallow nest box in detail first, then walks you through the barn swallow nest shelf separately. Pick the one that matches the species you are trying to attract and follow that plan.

Site selection and entrance dimensions: getting these right matters more than the wood you use

Tree swallows are birds of open space. They nest near water, meadows, and fields where they can hunt insects on the wing. If your yard backs up to a marsh, a pond, or even a large grassy area, you are already in good territory. The box should be placed in an open spot, not tucked into dense shrubs or under a tree canopy. NestWatch recommends mounting tree swallow boxes with the entrance facing east, and a Maine nest box monitoring program backs this up, recommending south or east-facing openings to catch morning warmth and avoid driving rain.

The entrance hole is the single most important dimension you will cut. For tree swallows, the correct entrance hole diameter is 1 3/8 inches (about 35mm). Some sources list 1 1/4 to 1 1/2 inches as an acceptable range, and a 1 1/2 inch hole will also work in a pinch, but 1 3/8 inches is the sweet spot backed by the most reliable guidance. This is not an arbitrary number. As Birds Canada explains, the entrance hole size and interior box dimensions are the primary factors that determine which species will actually occupy your box. Too large and you invite starlings and house sparrows. Too small and the swallows cannot get in. A 1 3/8 inch hole is large enough for a tree swallow and small enough to exclude most problem species.

For barn swallows, there is no entrance hole because the nest shelf is open. Instead, what matters is providing a sheltered location with something to anchor the mud nest to. A small wooden cone or a rough-surfaced shelf bracket under an eave works well. Barn swallows prefer structures near open water and farmland, and they are more tolerant of human activity than most birds, often nesting inside barns, garages, and covered porches.

Materials and tools you will need

For a tree swallow nest box, 3/4 inch red cedar is the best lumber choice. Cedar is naturally rot-resistant, weathers beautifully without paint or stain, and holds up for many nesting seasons. If cedar is hard to find or out of budget, untreated pine at 3/4 inch thickness works fine and is what a lot of commercial boxes use. Avoid treated lumber, plywood with exterior glues, or MDF. Those materials off-gas chemicals that are not safe for nesting birds. If you are repurposing scrap wood from another project, plain pine or fir boards are perfectly acceptable as long as they are untreated.

Keep in mind that when your lumber supplier says 1x6 board, the actual thickness is 3/4 inch (about 19mm). This matters when you are cutting your floor piece, because the interior floor dimensions need to hit 4 x 4 inches minimum, with 5 x 5 inches being ideal. If your lumber is slightly thinner or thicker than nominal, adjust your cuts so the interior space, not the exterior, hits those target dimensions.

• 3/4 inch red cedar or untreated pine boards (one 6-foot length of 1x6 is usually enough for one box)
• Exterior wood glue
• 1 1/4 inch or 1 5/8 inch exterior screws (galvanized or stainless steel)
• 1 3/8 inch drill bit or spade bit for the entrance hole
• 1/2 inch drill bit for drainage and ventilation holes
• Jigsaw or circular saw for cutting panels
• Drill/driver
• Sandpaper (80 and 120 grit)
• Tape measure and pencil
• A piano hinge or stainless steel screw for the cleanout panel (optional but recommended)
• Metal pole or wooden post for mounting
• Predator baffle (cone-style or stovepipe style)

For a barn swallow nest shelf, you will need much less material: a small piece of 3/4 inch board (roughly 6 x 6 inches), a few inches of scrap trim board to form a lip, exterior screws, and wall anchors or lag bolts depending on where you are mounting it. Some people glue a small rough-textured cone of hardware cloth or natural twine inside a recessed shelf to give barn swallows something to anchor their mud nest against. That small detail can make the difference between birds that investigate and birds that actually build.

Step-by-step build plan for a tree swallow nest box

This plan is based on the Henderson nest box dimensions, which are the most widely used and tested specs for tree swallows. The finished box has an interior floor of 4 x 5 1/2 inches, a box height of 9 inches, and an entrance hole positioned 6 inches above the floor. These proportions give tree swallows the interior space they need while keeping the entrance high enough to protect eggs and chicks from weather and reaching paws.

Cut your panels

1. Floor: 4 inches x 5 1/2 inches
2. Front panel: 5 1/2 inches wide x 9 inches tall
3. Back panel: 5 1/2 inches wide x 12 inches tall (the extra length lets you attach it to a post)
4. Two side panels: 4 inches wide x 9 inches tall, with the top cut at a slight angle if you want a pitched roof (not required but helps with drainage)
5. Roof: 6 inches x 7 inches (slightly oversized to overhang the front and sides)

Drill the entrance hole and add drainage

On the front panel, mark the center of the entrance hole so that its bottom edge sits exactly 6 inches above the interior floor. Drill a 1 3/8 inch round hole using a spade bit or Forstner bit. Take your time with this one, go slow, and back a scrap board behind the panel to prevent blowout on the exit side. If you want to add a predator guard (highly recommended), drill the same 1 3/8 inch hole through a second piece of 3/4 inch wood and screw it flush to the front of the panel so the entrance tunnel becomes 1 1/2 inches deep. This extra thickness makes it much harder for a raccoon to reach in and hook eggs or chicks.

On the floor panel, drill four 1/2 inch diameter holes near each corner. These drain any water that gets inside and also provide a small amount of ground-level ventilation. On each side panel near the top, drill two more 1/2 inch holes for upper ventilation. A well-ventilated box on a hot afternoon can mean the difference between a successful nest and overheated eggs. Do not skip this step.

Assemble the box

Attach the floor to the back panel first using exterior glue and two screws. Then attach the side panels to the floor and back. Attach the front panel last. If you want a cleanout panel (and you should, it makes annual cleaning much easier), attach one side panel with a single pivot screw at the top rather than gluing and screwing it all the way around. It will swing open for cleaning and snap shut for security. Attach the roof with a small overhang at the front and sides to keep rain off the entrance. Do not caulk or seal the interior. Leave it raw and rough-textured inside so birds can grip the walls and nestlings can climb toward the entrance when they are ready to fledge.

What about a barn swallow nest shelf?

A barn swallow shelf does not need a box at all. Cut a 6 x 6 inch flat platform from 3/4 inch board and attach a 1 1/2 inch lip along the front and sides to keep the nest from sliding off. Mount it under an eave, inside a garage or shed opening, or on a sheltered wall bracket at least 8 feet off the ground. The rougher the surface, the better the mud sticks. You can score the top of the platform with a saw blade or staple a small square of hardware cloth to the surface to give the birds something to work with. Unlike tree swallows, barn swallows are not particularly picky about the shelf design as long as it is sheltered from above and offers a clear flight path in and out.

Mounting, height, and placement

For tree swallow nest boxes, mount them 5 to 6 feet above the ground on a metal pole or a smooth wooden post. This height is easy for you to monitor and clean, and it puts the entrance hole right in the tree swallow's comfort zone. If you are mounting on a wooden post, attach a downward-facing cone-style baffle directly below the box, which is the mounting method Birds Canada specifically recommends to block climbing predators. A metal pole with a smooth surface works even better as a standalone deterrent. Avoid mounting tree swallow boxes on trees or fence posts, where squirrels and raccoons already have a highway directly to your box.

If you are putting up multiple tree swallow boxes (which is a great idea since they will compete for territory), space them at least 35 feet apart. This is the minimum spacing NestWatch lists for tree swallows in their placement guidance. Put boxes closer together and you will find that one dominant pair drives the others away and you end up with fewer nesting pairs overall, not more.

Orient the entrance hole to face east or south. This gives the box morning sun to warm the nest early in the day and keeps the worst driving rain (which usually comes from the west or north in most of North America) from blowing directly into the opening. Do not face the entrance toward the prevailing wind.

For barn swallow nest shelves, height matters more than pole mounting. Barn swallows build in existing structures, so you are really giving them an anchor point inside or under something they already want to use. Eight to twelve feet off the ground inside a barn, shed, or covered porch is a common and effective placement. The flight path to and from the nest should be clear of obstructions and ideally open to the outside without requiring the bird to navigate around walls or doors.

Swallow house comparison: tree swallow box vs. barn swallow shelf

If you are only going to build one thing, and you want the most reliable chance of a nesting pair using it this season, build the tree swallow nest box. Tree swallows are cavity-nesters by instinct and actively search for available boxes in late winter and early spring. A correctly built and mounted box in good habitat can attract a pair within the first season. Barn swallow shelves work beautifully but rely more on the birds already frequenting your property or nearby structures.

Cleaning, maintenance, and what to do when swallows do not show up

Clean your tree swallow nest box once a year, after the nesting season is completely over in late summer or early fall. Open the cleanout panel, remove the old nest material, and scrub the inside with hot water and a mild soap solution using a stiff brush. Rinse thoroughly and leave the box open to dry completely before closing it up for winter. For barn swallow shelves, the same basic approach applies: after the nesting season, scrub the shelf with hot water and mild soap, rinse well, and let it dry. Getting into the habit of a thorough annual clean is the single best thing you can do to prevent parasites and mites from building up between seasons.

Inspect the box each spring before the birds arrive, usually in February or March depending on your location. Check for cracked panels, loose screws, and any gaps that might let in rain or predators. Tighten everything up and check that the entrance hole has not been chewed larger by squirrels (it happens more than you would think). If you want to track nesting progress systematically, Cornell Lab of Ornithology's NestWatch program gives you a structured way to monitor nesting stages and record outcomes over multiple seasons, which is genuinely useful for spotting patterns in failed or successful years.

Troubleshooting: swallows are not moving in

If you have had a box up for a full season with no takers, run through this checklist before you give up or rebuild from scratch. The most common problems are almost always location and predator pressure, not the box itself.

• Is the box in genuinely open habitat? Tree swallows will not nest in wooded or heavily planted areas. Move the box to a more open spot if needed.
• Is there a predator baffle on the pole? A box without a baffle in areas with raccoons or cats will be raided, and once that happens swallows will not return to the same site.
• Is the entrance hole the right size? Measure it again. A hole that has been enlarged by squirrels or weathered slightly larger than 1 3/8 inches may be letting in competitors.
• Are house sparrows or starlings taking over? Remove their nests promptly. Tree swallows will not compete with established sparrow pairs for the same box.
• Is the box facing the right direction? Try reorienting to face east or south if you had it pointing west or north.
• Are you in tree swallow range and habitat? Near open water, marshes, and meadows is ideal. If your yard is in dense suburban development with no open water nearby, tree swallows may simply not pass through.
• Did you install the box too late? Tree swallows scout for nest sites as early as late February in warmer climates. Get boxes up by late winter for the best chance.

One thing that often surprises people is that a box can sit empty for a year or two before swallows discover it. Do not pull it down after one empty season. Leave it up, keep it clean, and give the birds time to find it. Once a pair nests successfully, they will often return to the same box the following year.

A few more species worth building for

If you enjoy this kind of project, it is worth knowing that the same basic cavity box design opens the door to several other species with only small adjustments to hole size and interior dimensions. If you have doves around your property, you can adapt the open-shelf concept into a dove bird house using a similar platform design. For smaller cavity nesters, you might enjoy tackling a finch bird house, which uses a narrower entrance hole and a more compact interior. House sparrows are everywhere, and if you want to support native sparrows instead, the guide on how to build a sparrow bird house covers the right specs to attract them specifically.

If starlings are already competing for boxes in your yard, it is useful to understand their nesting habits too. The article on how to build a starling bird house explains their preferred dimensions, which can help you design your swallow box to exclude them by keeping the entrance hole at the right size. For aerial insect hunters in a similar niche to swallows, building a chimney swift bird house (actually a tower) is a fascinating next project. Chickadees are another great candidate for the same open field habitat: take a look at the details on how to build a chickadee bird house if you want to put up a second box for a different species. And if you want to go all-in on the most colorful tenant possible, building an oriole bird house is a rewarding challenge with its own specific design requirements.

The bottom line: pick your species, cut your panels to the right dimensions, drill a 1 3/8 inch entrance hole, add drainage and ventilation, mount it on a baffled pole in open habitat facing east or south, and keep it clean every fall. That is genuinely all it takes to give swallows a home they will want to use. You can absolutely do this in an afternoon with basic tools and a single board of cedar.