The advice below describes general principles to consider when providing new roost spaces for bats in a building, as opposed to providing roosts in the form of bat boxes. It does not provide sufficient information for mitigation when a roost is already present. Work on existing roosts should be covered by an EPS licence from the relevant Statutory Natural Conservation Body.
Access, size of roost space and structure
• Crevice-dwelling bats can crawl into their roosts via gaps from as small as the width of our thumb. The roost area should contain a crevice of this approximate size gap that the bats can roost in. The height of entry can be from 2 - 7m.
• Roof-void dwelling bats require similar dimensions to access the roost but typically need timber joists or beams on which to roost. The height of entry can be from 2 - 7m.
• Bats needing a flying area require the same access dimension as mentioned above. These areas are typically empty / uncluttered loft spaces to allow flight.
• Horseshoe bats need a larger access so that they can fly (instead of crawl) directly into the roost. As above, the roosting area should not be trussed / cluttered, to allow flight.
Materials and structure
Materials for the roosts should be rough (for grip), non-toxic or corrosive, with no risk of entanglement. The materials should also have suitable thermal properties that reduce 24 hour fluctuations but allow maximum thermal gain for summer roosts.
Useful resources:
Bats and Buildings
John Black
