Preliminary Roost Assessment

Preliminary Roost Assessment (PRA): The First Step in Satisfying Legal Obligations

In the current planning climate, missing a single environmental technicality can derail a proposed development before the first brick is laid. For private developers, social housing providers and even homeowners seeking planning permission, bat surveys have become a critical and often misunderstood part of the pre-construction phase.

Whether you are overseeing a large-scale estate regeneration, a sensitive barn conversion, or a minor extension, the local planning authority (LPA) is legally bound to consider protected species. In most instances, the Preliminary Roost Assessment (PRA) is the first and most vital step in satisfying these legal obligations and securing planning permission.

What is a Preliminary Roost Assessment?

A Preliminary Roost Assessment, frequently referred to as a “Stage 1 Bat Survey” or a “Bat Scoping Survey”, is an initial site appraisal conducted by a licensed ecologist. Its primary goal is to identify evidence of bat activity or features within a building that could support roosting bats.

Unlike secondary “emergence surveys,” which are strictly seasonal, a PRA can be conducted all year round. This makes it an essential tool for project managers looking to maintain momentum during the winter months.

What the Surveyor Looks For:

Physical Evidence: This includes bat droppings, urine staining or feeding remains.

Potential Roosting Features (PRFs): Surveyors examine a building’s suitability to find as much information as possible about its potential for hosting bats. Bats often exploit small gaps that are invisible from the ground, such as:

• Missing or slipped roof tiles.

• Gaps in fascias, soffits and bargeboards.

• Internal voids and loft spaces.

• Cracks in weatherboarding or hanging tiles.

When Does a Project Trigger a PRA?

A local authority will typically require a bat survey if a proposal involves the modification or demolition of structures that meet certain criteria and could impact bats. High-risk projects include:

• Conversion or Demolition: Particularly of older or traditional buildings.

• Roof Works: Any modification to loft spaces or the removal of roof tiles.

• Rural Developments: Sites located near woodland, water, or significant foraging habitat.

• Tree Works: Removal or pruning of “veteran” trees with hollows or cracks.

Under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, it is a criminal offence to recklessly disturb or destroy a bat roost. A PRA provides the “trustworthy proof” required by councils to ensure the development is compliant if there are potential impacts for bats.

The Four Stages of a Preliminary Roost Assessment Survey

A professional preliminary roost assessment survey is a rigorous process designed to stand up to the scrutiny of planning officers. According to preliminary roost assessment guidelines, it comprises:

1. The Desk Study

Before visiting the site, an ecologist reviews historical records. They check for known roosts in the vicinity and analyse the surrounding landscape for foraging “corridors,” such as hedgerows or waterways.

2. External and Internal Inspection

The ecologist performs a physical audit of the site and surrounding area. Externally, they walk the perimeter looking for potential access points. Internally, they focus on loft spaces and dark voids, looking for potential roosting sites using high-powered torches, bat detectors and endoscopes to investigate deep crevices.

3. Suitability Categorisation

The site is assigned a category based on the findings:

• Negligible Suitability: No features likely to be used by bats.

• Low/Moderate/High Suitability for Roosting Bats: Features are present, even if no bats are seen during the visit.

• Confirmed Roost: Clear evidence of bats is found.

4. The Final PRA Report

The resulting PRA report outlines the findings and, crucially, the mitigation strategy. Unless the finding is a likely absence of bats, mitigation measures might be needed. These could include “bat-friendly” lighting (warm-spectrum LEDs ≤2,700K) or the installation of bat boxes. If the site is deemed to have roosting potential, the report will recommend further surveys such as Bat Emergence Surveys (BERS), which involve dusk and dawn re-entry surveys, or even hibernation surveys for certain bat species.

Managing Timelines: The “Seasonality” Factor

The most significant risk to development proposals and a housing timeline is failing to account for Stage 2 bat activity surveys. If a PRA finds “moderate” or “high” suitability, you must conduct emergence surveys. These can only be performed between May and September.

By commissioning preliminary bat roost assessments early (even in the winter), developers can identify these requirements ahead of time, ensuring they don’t miss the summer survey window and face a six-month delay.

Professional Support with Survey Work

Navigating environmental red tape shouldn’t be a source of frustration. To keep your housing project moving and avoid unexpected planning obstacles due to further survey work, the best way is to find out the exact requirements stipulated by your local authority when it comes to bat surveys and mitigation.

If your site requires a European Protected Species Licence (EPSL) due to a confirmed roost, expert ecological consultants holding a bat licence will be able to advise you about the application process with Natural England or Natural Resources Wales

To give your planning application its best chance to secure planning permission and avoid delays, obtaining this advice and following best practice guidelines at an early stage will be advantageous.