Bat surveys and historic buildings

Historic buildings are hugely inviting to bats simply because their fabric often provides gaps for them to access, and they have lots of roof space which is ideal for bat roosts. There’s less likelihood of finding bats in modern, airtight buildings as they have fewer gaps in the construction materials, therefore less opportunity to support bats.

Historic buildings provide ideal habitat for UK bat species.

Protection for bats

Bat population numbers have fallen steeply in the UK as their natural environment has been lost due to modern farming techniques, urban development, and loss of green space. This has made historic buildings ever more appealing to bats, especially as their surroundings often include mature gardens, farmland, woodland, water, foraging habitat and other potential roost sites. Such traditional and historic buildings are often in rural communities and may include period properties, listed buildings, churches, cellars, livestock buildings and scheduled ancient monuments.

And it’s often the owners of such buildings who seek planning permission to make them viable for the future, as they aim to convert or refurbish them, and this is where bats come to the forefront.

Bats are a protected species under the Wildlife and Countryside Act 1981 (as amended) and the Conservation of Habitats and Species Regulations (2017), which make it an offence to harm bats, intentionally kill or disturb them. It is illegal to deliberately capture bats, damage or destroy their habitat or obstruct access to their resting places.

There are 18 species of bat native to the UK according to the Bat Conservation Trust, ranging from the most abundant, the common pipistrelle, to the rarer Bechstein’s bats.

Getting bat survey work done before any work starts on your development scheme is important; if you find bats when the project is underway can put you at risk of prosecution and be both costly and time-consuming to sort out.

A bat survey can provide options for managing bats

If there’s a high potential for bat activity in or around your development project, you will need a bat survey. A bat survey report will usually be an essential part of your planning application as your local planning authority will request evidence of bat mitigation in your plans as part of the planning process.

However, the presence of bats in a historic building need not scupper your development plans. Following a bat survey, mitigation and compensation measures can allow modifications and repairs so that bats can continue to live there. You might have to take a different approach to avoid disturbing bats. It’s also a good idea to be proactive, improving habitat and adding roosting opportunities where you can as soon as possible.

Local planning authorities will have their own biodiversity checklists which you can consult to find out what their requirements are, and what expert advice and reports you’ll need before submitting a planning application. When you get your bat survey, it’s worth noting that Natural England will view it as having a two year shelf life.

Properties such as this listed railway building might well support roosting bats.

Bat surveys

A bat survey is likely to be needed for historic sites where the planned work involves conversion or restoration of traditional farm buildings, especially those with wooden beams; pre-1960 detached buildings close to water or woodland; pre-1914 structures; Dutch barns and buildings that are weather boarded, near woods or water providing foraging areas.

Preliminary Roost Assessment (PRA)

If you need a bat survey, in the first instance you will need a Preliminary Roost Survey or scoping bat survey which will establish whether there are bats present. This initial assessment can be undertaken at any time of year by licenced bat specialists who will look for evidence of bats, including bat droppings, urine stains, dead bat carcasses, feeding remains, and potential roosting features such as roof voids, hanging tiles and slate roofs. If the Preliminary Roost Assessment shows evidence of the presence of bats, a second stage full bat survey will be needed, known as a Bat Emergence Survey.

Bat Emergence Survey (BERS)

It’s important to be aware that Bat Emergence Surveys can only be carried out in the bat survey season, between May and September, the optimal months for bat surveys as they are outside the bat hibernation season. BERS must be carried out in daylight hours, 15 minutes before, or two hours after sunset; two hours before or 15 minutes after sunrise. Bat survey guidelines state that two or three surveys over the summer may be needed to collect the required information. To monitor all sides of a building, two or three surveyors may be needed on site to record bats. They will look at access points where bats emerge from and re-enter the building, flight paths, and potential sites which may include day roosts, night roosts, transitional roosts, hibernation roosts, maternity roosts, and foraging roosts.

Best practice involves bat surveyors carrying out an internal and external inspection of the site. If bats are present, the ecologist will identify the species and type of roost, and their bat survey findings will contain appropriate mitigation measures: these could include a habitat enhancement plan and mitigation measures which could allow your development proposals to proceed. If you are then granted planning consent by your local planning authority, you can apply for the required bat mitigation class licence which will allow you to continue, based on the mitigation proposals and other evidence in the bat survey.

Mitigation work may include safely relocating bats, or avoiding bat roost areas during the development works. Installing bat boxes or fitting bat access tiles on buildings may also be recommended. Bat activity surveys can be cancelled due to adverse weather conditions such as heavy rain or high winds, so surveys should be booked in in good time to allow for this.

Bat survey equipment

Bat surveyors use various specialist equipment to assess the number of bats present, including voice recorders that convert bats’ echolocation calls into a frequency readout that aids species identification. Other equipment includes bat detectors, night vision and thermal imaging cameras.

Bats are often found in loft space.

Works to historic buildings that may require a bat survey

  • Alterations to bridges, industrial chimneys, ice houses, and cellars.
  • Re roofing and chimney repointing.
  • Repointing walls, rewiring, and repairs to doors and windows.

Works that may disturb bats include:

  • Replacing or removing fascia boards or soffit boxes. This can be mitigated by creating crawling bat access, and by leaving a small space underneath the new replacement structure that bats can use.
  • Felling trees or work to repair gaps in timber that could be used by crevice dwelling species of bat. Replacement crevices could be created.
  • Demolition noise should be minimised by using extra insulation.
  • Floodlighting of sites close to woods, water and fields. Bats are sensitive to lighting, and it can interfere with their commuting and foraging routes. Aim to keep a dark corridor around at least part of the building.
  • If work is taking place on a building used for night roosting, access gaps for bats can be kept over doors, or by leaving some open frontage.

Permitted development rights

The relevant legislation protecting bats and their natural habitats must still be observed when dealing with permitted development rights schemes that don’t require a planning application.

Visitors to buildings where bats are present

If your historic building receives visitors regularly, plan to minimise their contact with areas where bats may be present where possible. Of course, this is easier in big spaces such as a church, than in smaller buildings, where measures such as public access at only certain times of the year might need to be considered.

Book your bat survey in good time

If you need a bat survey as part of your development proposals, it’s important to book your survey with a specialist firm such as Arbtech in good time to prevent delays to your time frames, as outlined above. Contact your local planning authority early to find out what they will expect you to provide, and speak to a professional ecologist with a bat licence who will be able to give further advice and detailed guidance, as well as provide a bat survey cost indication.

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