Tree Swallow Nest Box — Cornell Lab Spec | No Supports | Tool-Free Roof

A functional, field-spec nest box designed specifically for Tree Swallows (also suitable for Violet-green Swallows), built to Cornell Lab / NestWatch dimensions. Every feature has a reason — this isn't a decorative birdhouse.

Why this design?

Most 3D printed birdhouses are decorative. This one is built to actually attract and protect cavity-nesting birds. Dimensions, hole size, and ventilation all follow published NestWatch guidelines for Tree Swallows.

Features

• 4" × 4" × 6" interior — correct spec for Tree and Violet-green Swallows
• 1.5" (38.1mm) entry hole — admits swallows, excludes European Starlings
• Chamfered predator guard collar — 55mm square collar with a 45° chamfered bottom face. Discourages cats and raccoons from reaching in. No overhangs = no supports needed
• Interior ladder ridges — horizontal ridges below the entry hole give fledglings grip to climb up and exit
• Ventilation — 4× 5mm holes in the side walls near the top to prevent heat buildup
• Drainage — 4× 7mm floor holes, offset so they can't be blocked by nesting material
• Mounting flange — back wall extends 70mm above the box with 6 screw holes for solid post or board mounting. Use a pole-mounted predator baffle for best results
• Tool-free removable roof — rear U-slot straddles the mounting flange; two front locating pegs snap into blind holes in the roof. Press down to seat, pull up to remove. Clean out every autumn before birds return

Print Settings

Body — print upright, floor on build plate, open top facing up Roof — print flat, smooth inner face down

Both parts fit on a standard 256mm bed with room to spare.

Assembly

1. Mount the body on a post or board through the 6 flange holes (recommend 5–6ft height with a predator baffle on the pole)
2. Lower the roof straight down — the rear slot self-locates over the flange
3. Press the front down until the pegs seat

That's it. No screws, no tools.

Placement Tips

• Mount in the most open part of your yard with clear flight paths in and out
• Face the entry hole away from prevailing wind (east or southeast in the Pacific Northwest)
• Near open water or fields is ideal — Tree Swallows hunt flying insects on the wing
• Two boxes 15–20ft apart can host both a Tree Swallow and Violet-green Swallow pair simultaneously

Files

• body.stl — box with integrated floor, entry hole, predator guard, flange, and pegs
• roof.stl — shed-style tapered roof panel with rear slot and peg holes