Thick 18 mm pallet boards keep the inside steady through cold nights and hot afternoons, which is exactly what nesting birds need. The roof overhangs the front to keep the rain off the hole, and there's no perch: birds don't need one, and perches only help predators.

The front swings open on two pins, held shut by one screw, so you can clean it out in autumn. Small holes in the floor let any water drain away. The inside is left bare wood; only the outside is oiled.

Choose the hole for the birds you'd like to see: 25 mm for blue tits, 28 mm for great tits, or 32 mm for house sparrows.