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.