If your project touches an older roof, a barn, an outbuilding or mature trees, the words “bat survey” may appear on your planning conditions. Here is what that means, in plain terms, and how to stop it delaying your build.
Bats are one of the most common reasons a straightforward home project meets an unexpected condition. It catches people out because the survey can only be done at certain times of year, so a badly timed application can lose you a whole season. The good news: handled early, a bat survey is a routine step, not a roadblock.
Why a bat survey is even needed
All UK bat species and their roosts are protected by law, whether or not a bat is present at the time. Under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, bats are a European Protected Species. It is an offence to harm a bat, or to damage or block a place they use to roost, even a roost that is empty when you find it. Because roofs, soffits, gable ends, old barns and mature trees are exactly the kinds of places bats use, a planning authority will often ask for a survey before it grants permission for work that affects them.
Councils in the Farnham, Waverley and wider Surrey and Hampshire area apply this routinely to loft conversions, roof works, barn conversions, extensions to older buildings, and demolition. If your planning officer has asked for one, it is a standard requirement, not a sign that anything is wrong.
The three kinds of survey, and when each can happen
There are three stages, and the timing rules are the single most important thing to understand, because they decide when your project can start.
1. Preliminary Roost Assessment (PRA)
This is the first step and can be done at any time of year, in daylight. An ecologist inspects the building or trees for signs of bats and for features they could use, and rates the site as negligible, low, moderate or high potential. For many homes, if the assessment finds negligible or low potential and no evidence, this is as far as it goes. If it finds moderate or high potential, further surveys follow, and those are the ones tied to the season.
2. Emergence and re-entry surveys
These are the dusk and dawn surveys where ecologists watch the building to see whether bats fly out or return. They can only be carried out between May and September, when bats are active, with the best results from May to August. A building of moderate potential usually needs two visits; high potential usually needs three, spaced at least two to three weeks apart. This is the stage that most often holds a project up, because if your PRA lands in October, you may wait until the following May to complete the work.
3. Hibernation surveys
Less common for domestic projects, these check for hibernating bats and can only be done in the core winter months, roughly December to February. They are usually reserved for larger or higher-risk sites.
The rule that catches people out
The preliminary assessment can happen any time, but the dusk and dawn surveys that often decide the outcome are locked to May to September. Miss that window and you can lose the best part of a year. The single best move is to book the assessment early, in winter or early spring, so any further survey can be slotted into the coming season rather than the one after.
The survey season at a glance
Guide only. Your ecologist will confirm exactly what your site needs. Windows can shift slightly with the weather in a given year.
What happens if bats are found
Finding bats does not stop your project. It changes the route to it. What it means in practice:
- A mitigation licence is usually needed. If a roost is confirmed and your work would disturb it, the ecologist applies to Natural England for a European Protected Species mitigation licence. This makes the work lawful under agreed conditions.
- You get a mitigation plan. This sets out how the work is done safely: often careful timing to avoid sensitive periods, a soft strip of the roof under supervision, and replacement roosting provision such as bat boxes, access tiles or a dedicated roost space.
- Works are timed around the bats. Sensitive operations are scheduled outside the breeding season (roughly June to August) and outside hibernation, with the ecologist advising on exact dates.
- An ecologist may attend on site. For higher-risk roosts, an ecologist supervises the sensitive stages of the work.
When can the actual building work start
If no bats and no roost are found, you are usually clear to proceed once the survey report discharges the planning condition. If a roost is found, work affecting it can begin once the mitigation licence is granted and any timing conditions allow. Natural England aims to decide a licence within around 30 working days of a valid application, though it can run longer at busy times, so it is sensible to build several weeks into your programme for it. Work elsewhere on the project that does not affect the roost can often continue in the meantime.
How to keep bats from delaying your build
- Book the preliminary assessment early. Ideally over winter or early spring, so any emergence surveys can be done in the May to September window of the same year.
- Flag it at the design stage. If your project touches a roof, an outbuilding or mature trees, assume a survey may come up and plan for it from the start.
- Use a licensed ecologist. The surveys and any licence must be handled by a suitably licensed professional. A good report is what actually discharges the condition.
- Keep your programme flexible. Build the survey season and the licence timeline into your schedule rather than assuming an immediate start.
Trusted ecologists near Farnham
If you need a bat survey, here are established ecological consultancies working in and around Farnham. Contact them directly for a quote; we are happy to coordinate with whoever you appoint.