Thick, solid, untreated timber — no zinc, no tar, no felt, no dark coat. The mass holds a steady temperature through a July afternoon instead of climbing into the range that finishes a nursery in a thin box. “I spent forty years keeping roofs cool and dry,” Malcolm says. “Same job. Smaller.”

Inside is a crack, not a room. The grooves are cut tight enough that the animal’s back and belly both touch wood at once — the pressure that tells it it is safe. Most boxes give them an open chamber, and an open chamber reads as exposed ground.

A bat never goes in at the front. It lands low, then climbs up through the open bottom — exactly the way it would go up under a slate. The gaps you can see between the logs are structure, not doorways. Getting this one thing wrong is why so many boxes never get used.

No membrane, no weave, no fabric, no loose fibre anywhere on it. Research by the University of Reading with the Bat Conservation Trust found that non-woven breathable roof membranes pose an entanglement risk to bats. Malcolm builds the deliberate opposite: solid timber and bark, nothing a claw can pull free.

Fallen oak and sweet chestnut off the valley floor — two of the few British timbers that last outdoors with nothing at all put on them. No stain, no preservative, no sealant. Nothing to off-gas, and nothing the animal has to breathe in a sealed cavity all day.

Drawknife, brace and mallet instead of a router. Slower, quieter, and no cracked seams to open in the first wet winter. Every box is cut, bored and grooved by Malcolm himself — about two days of work in each one, and no second batch once the stack is gone.