It's one of the more common surprises in the planning process. You submit an application — a loft conversion, a barn conversion, a demolition, a re-roof, some tree work — and back comes a condition or a request: a bat survey is required before the application can be determined. It can feel like an obstacle. It needn't be, provided you handle it early and properly.
Why bats trigger a survey at all
All UK bat species and their roosts are legally protected under the Wildlife and Countryside Act 1981 (as amended) and the Conservation of Habitats and Species Regulations 2017. A roost is protected whether or not bats are present at the time, because they return to the same places year after year. Local planning authorities have a legal duty to consider protected species before granting permission — which is why, where there's a credible chance bats could be affected, they ask for survey evidence up front rather than after the fact.
What kinds of work tend to flag it
- Conversions or demolition of barns, outbuildings and older buildings
- Roof works, re-roofing, loft conversions, and works to soffits, fascias and gable ends
- Works to or felling of mature trees, particularly those with cavities, splits or dense ivy
- Conversions of structures near woodland, watercourses or open countryside
It starts with a Preliminary Roost Assessment
The first step is almost never a full survey. It's a Preliminary Roost Assessment (PRA) — a daytime inspection of the building or tree by a licensed ecologist, looking for the features bats use and any evidence they're present. The PRA grades the roost potential, typically as negligible, low, moderate or high. That grade determines what, if anything, happens next.
A PRA can be carried out at any time of year. If it finds negligible potential, that may be the end of it. If it finds low, moderate or high potential, you'll need follow-up surveys — and those are tied to the season.
If follow-up surveys are needed, timing matters
Where the PRA identifies roost potential, the next stage is emergence and re-entry surveys: ecologists watching the structure at dusk and dawn to see whether bats emerge or return. These can only be done when bats are active — broadly May to September. The number of visits scales with the roost potential found:
- Low potential — usually one survey visit
- Moderate potential — usually two visits, spread across the season
- High potential — usually three visits, spread across the season
This is the part that catches people out. If your PRA flags moderate or high potential in, say, late September, the survey window may already have closed for the year — which can stall an application until the following spring. The single most useful thing you can do is start early.
What it costs, and what you get
Cost depends on the building or trees, the access required, and how many follow-up surveys the roost potential dictates. A PRA is a modest fixed piece of work; follow-on surveys add cost per visit. For private clients we provide a full written report — everything a planning authority needs to see, written to the standard they expect, so it comes back accepted rather than queried. We'll give you a clear scope and cost before you commit, including the likely number of surveys, so there are no surprises later.
What to do next
If you've been asked for a bat survey, send us the location, the building or trees involved, and your rough timescale. We'll tell you what's needed, whether the season is on your side, and what it will cost — quickly, and without the preamble.