Is it the planning authority requiring a bat survey? Ask them to clarify how they consider that a bat roost might be disturbed by your proposal.
This is what the councils ecologist has said. I have also reviewed the previous application and considered the site context.
It is now nearly 9 years since the previous survey was undertaken and several years since the building was converted. The mitigation strategy for the conversion noted several elements of bat mitigation which could be affected directly and indirectly by the proposals; e.g. slits on the north gable will be lost, ridge tiles will be extremely close to the areas where works would be undertaken and there could be arising disturbance issues.
Therefore, it is considered that a bat survey undertaken in accordance with best practice is required to inform the application. The survey should commence with an inspection by an appropriately experienced ecologist but it is highly likely that activity surveys would also be required.