When Are Bat Surveys Required and What is Involved?

Understanding when bat surveys are required is an essential part of preparing a planning application. Bats are protected in the UK, and development projects that affect bats or their roost sites can face significant delays if surveys are not carried out at the correct stage.

For developers and landowners, early clarity reduces risk. Knowing when a survey is needed, what it involves, and how it fits into the planning process helps ensure smoother engagement with Local planning authorities (LPA) and compliance with environmental legislation. In many cases, uncertainty around bat surveys causes more delay than the surveys themselves. With the right advice at the outset, the process is usually straightforward and manageable.

Bat considerations are not limited to large-scale schemes. Even modest residential extensions or agricultural building conversions can trigger survey requirements. Understanding the triggers early helps avoid costly redesigns or seasonal delays later in the programme.

All species of bats in the UK are protected as European Protected Species under the Conservation of Habitats and Species Regulations 2017. They are also protected under the Wildlife and Countryside Act 1981.

This level of protection reflects the significant decline many species of bats experienced historically due to habitat loss, agricultural intensification and building alterations. Today, the legal framework is designed not only to prevent harm but to maintain the favourable conservation status of bat populations across the country.

It is illegal to:

• Deliberately capture, injure or kill a bat
• Damage or destroy a bat roost
• Obstruct access to a bat roost site
• Disturb bats in a way that affects their ability to survive or reproduce

Importantly, a bat roost is protected whether bats are present at the time or not. This means that even buildings with historic or occasional bat use must be properly assessed before works begin. A structure does not need to host a large colony to be legally protected; even a single roosting bat can trigger regulatory requirements.

Bat surveys are typically required where a proposed development has the potential to affect bats or their roost sites. This may arise where a planning application involves:

• Demolition or alteration of buildings
• Roof works, especially where there are features such as hanging tiles
• Works to barns, outbuildings, bridges or older properties
• Removal of trees, particularly those close to woodland
• Development close to known roost sites

Local planning authorities will usually request bat survey information where there is a reasonable likelihood that bats could be present. In many cases, this requirement is triggered following a Preliminary Roost Assessment.

It is important to recognise that survey requirements are risk-based. A modern building with no roof void and limited surrounding habitat is unlikely to require further survey work. Conversely, a traditional barn close to woodland or water presents a higher likelihood of supporting a bat roost.

Early discussion with your LPA and ecological consultants can help confirm whether bat surveys are required before submitting a planning application. This proactive approach prevents validation delays and ensures the correct information accompanies the application from the outset.

The first stage in determining whether bat surveys are required is usually a Preliminary Roost Assessment (PRA).

During this stage, an ecologist will:

• Undertake a desk study reviewing existing records
• Inspect the building or trees for features suitable for different roost types
• Assess the surrounding habitat for suitability, such as proximity to woodland or water
• Identify any evidence of bat activity, including droppings or staining

The assessment is typically a daytime inspection and does not involve observing bats in flight. Instead, it focuses on identifying potential roost features such as cracks, lifted tiles, soffit gaps or tree cavities that could allow bats to access sheltered spaces.

The outcome of the Preliminary Roost Assessment determines whether further surveys are necessary. If no suitable features are identified and no evidence of bats is found, additional surveys may not be required.

If potential roost features are present, further survey work will usually be needed to establish whether bats are actively using the structure and, if so, in what capacity.

Where a building or tree has the potential to support a bat roost, additional surveys are carried out during the active bat season (typically May to September).

The most common follow-up surveys are emergence and re-entry surveys. These are dusk and dawn surveys undertaken to confirm whether bats are using the structure. Ecologists observe the building at sunset (emergence) or sunrise (re-entry) to record bats leaving or returning to the roost. Multiple visits are often required to meet guidance set by Natural England and the Bat Conservation Trust, particularly where higher value roost types are suspected.

Where development affects habitats that bats use for commuting or foraging, a bat activity survey may also be required. These surveys assess how bats use the wider development site, not just the building itself. Automated detectors or walked transects may be used to record species of bats present and their activity levels.

Survey results will also identify the type of roost present, such as day roosts, transitional roosts, maternity roosts or hibernation roosts. The type of roost significantly affects what mitigation measures will be required, as maternity roosts and hibernation roosts typically require more robust protection.

If surveys confirm that bats are present, the development cannot proceed without appropriate mitigation.

This may involve:

• Retaining roost features within the design
• Installing bat boxes or bat lofts
• Timing works to avoid sensitive periods
• Applying for a bat mitigation licence from Natural England

A bat mitigation licence is required where works will damage or destroy a roost site. The licence application must demonstrate that the development is necessary, that there is no satisfactory alternative, and that the favourable conservation status of the species of bats will be maintained.

Mitigation is usually integrated into the design of the scheme. In many cases, with early planning, ecological enhancements can be incorporated without high cost or impact on viability. Without a licence in place, works affecting bats would be unlawful and could lead to enforcement action.

Local planning authorities must consider the presence of European Protected Species when determining planning permission. If a development is likely to affect bats, survey information must accompany the planning application.

Failure to provide adequate bat survey information can result in delays in validation, refusal of planning permission, or requests for additional surveys outside optimal seasons.

Because surveys are seasonal, missing a survey window can delay development projects by several months. This is often where projects encounter difficulty, not because bats are present, but because surveys were not commissioned early enough in the process.

Integrating ecological assessment into early feasibility stages is therefore best practice and helps maintain programme certainty.

Certain development sites are more likely to trigger bat survey requirements. These include older buildings with loft spaces, agricultural barns, properties with hanging tiles or weatherboarding, and sites close to woodland, rivers or green corridors.

Even minor alterations, such as roof repairs or extensions, can affect bats if roost sites are present. Developers should not assume that small-scale works are exempt from ecological consideration.

Bat surveys are constrained by season. Emergence and re-entry surveys must take place during the active season when bats are present and active. This typically runs from May to September, although precise timing depends on weather and survey type.

Winter surveys may identify hibernation roosts in certain structures, but activity surveys cannot be reliably undertaken outside the core season.

Applications submitted without the correct seasonal survey data may be delayed until the following survey window. Planning programmes should therefore allow sufficient time for survey work and potential follow-up visits.

Understanding when bat surveys are required is about more than compliance. It is about managing risk, avoiding delay and ensuring that development proceeds responsibly.

At Collington Winter Environmental, we support developers and landowners through every stage of the bat survey process. From Preliminary Roost Assessments to emergence surveys and mitigation strategy design, our approach is proportionate, clear and aligned with local planning authority expectations.

If you are preparing a planning application and are unsure whether bat surveys are required, contact Collington Winter Environmental today via info@collingtonwinter.co.uk or by filling out our contact form below for professional advice and early-stage guidance.

For Good Practice Guidance for Bats, visit the Chartered Institute of Ecology website.