If evidence of bats is found in a building during a preliminary bat survey or there is potential for bats to be present in unseen locations, e.g., above wall tops or under ridge tiles, bat emergence surveys will be required to give confidence to a negative assessment or categorise any roost, in accordance with bat survey guidelines (Collins 2016).
Bat emergence surveys can be undertaken between May and September, although the optimal time is from May to August. Surveys should be spaced a minimum of two weeks apart, preferably four for a better spread. If a bat licence is required for proposed work, Natural England normally require (as a minimum) two bat emergence surveys undertaken within the current or most recent optimal survey period. It may be possible to get a licence with one survey in the optimal period and a second survey in September.
The type of licence required will depend on the results of the surveys. If only a small number of common species are found to be using the structure, it should qualify for a Bat Low Impact Class Licence (BLICL).