Bats and their roosts are highly protected, so how do you work around bats on site?

Bats are the most common of all the protected species that could affect your building project. Whether you’re embarking on a home extension, conversion, refurbishment, demolition or new build – if there is the possibility of bats in or near  your home, then you will need to take them into account as part of your project design and build.

With thanks to Daniel Ahern Ecology for help with this article

Image supplied by Daniel Ahern Ecology

Where do bats roost?

Bats can be found  in buildings, trees, close to woodland, water and even roosting underground. All 18 UK bat species and their habitats are protected under the Wildlife and Countryside Act 1981 and European legislation.

It's not just a criminal offence to deliberately kill bats but also to disturb these creatures in their places of shelter or to deliberately block access to a roost.  When planning officers consider your application, they will assess the likelihood of bats being present and harmed by your proposals. Bat surveys may be required along with compensation or mitigation measures.

The presence of bats rarely scuppers a building project, but it can make it more complicated and expensive. If bat surveys aren’t conducted at the appropriate time, your planning application can be delayed or even refused. If the bats need to be disturbed or rehomed, then this must be done by a specialist with a bat licence.  Flouting the law can result in heavy fines or even a prison sentence, so it needs to be taken seriously.

When is a bat survey necessary?

A bat survey is needed when there is a “reasonable likelihood” of bats being present and impacted by your project.  Generally, older or unused buildings, structures with uneven roof tiles and large roof timbers, or cracks and small openings are likely to attract bats.

Any building work involving the attic, roof void or roof tiles has the potential to impact bats, said ecologist Daniel Ahern. Bats fall into two groups: crevice dwellers, these are smaller species (common pipistrelle) and void dwellers, or the larger species (brown long-eared bats). Ahern said: “Crevice dwellers may never be seen in an attic and a homeowner may be completely unaware of them. There may be no evidence of them roosting in the structure as they will be roosting between tiles and the felt, or under the lead flashing around a chimney. Void dwellers are much more likely to be evident inside the attic, either a bat or its droppings or feeding remains.”

A local planning authority is also likely to want a survey if your property is close to woodland or water where bats might roost. Ahern said: “The less developed an area is, the more likely we are to encounter bats. There’s more for them to eat and more places to roost undisturbed. From experience I would expect urban or rural extensions would be asked for a bat survey by the planning authority.”

Trees featuring natural cavities, such as ash, beech or oak, can also harbour bats. Tree felling for a project could affect a bat roost. Even if you keep the tree, building work could still disturb the roost.

Phase 1 bat survey

If bat presence is considered possible, your local planning authority will request an initial check sometimes known as a ‘Preliminary Roost Assessment’ (PRA) or a ‘Phase 1 Bat survey’ be carried out. This involves a site visit and inspection by a qualified ecologist. “A PRA assesses how likely it would be for bats to use a building as either a daytime sleeping place for summer months, a place to give birth in May/June (maternity roost) or a winter hibernation roost,” said Ahern on his website.

Your ecologist will carefully search for any evidence of bat activity, such as bat droppings or feeding remains, as well as access holes.  Bat droppings may be sent off for DNA analysis to identify which species of bat are present. A PRA identifies buildings as having either high, low or negligible bat roost potential.

“If a building has negligible potential, no further surveys are required and a report can be submitted by the ecologist to the local planning authority to support your planning application. If the building is assessed to have high, moderate or low roost potential, further surveys are needed,” said Ahern.

For loft or barn conversions, roof works (reroofing or remodelling), recladding or total demolition of existing buildings, it is likely that your ecologist will conclude there is a reasonable chance of bat roost potential, so further survey work would be required.

Phase 2 bat survey

The second part of a bat survey will establish if there is an actual presence of bats. A variety of different names are used to describe this step – it might be called a ‘Bat Activity Survey or ‘Phase 2’ Survey’  or ‘Bat Emergence Survey.’ This can delay your project because your ecologist will need to visit two or three times at different times of the year.

The bat activity survey can only be carried out between around April and September because these creatures hibernate in winter.  So, there’s a limited window in which this work can be done. If a council decides in October, for instance, you should have submitted a bat survey, your planning application could be delayed by six months or more. Long delays are the last thing most people want to avoid, so it’s important to engage with an ecologist as soon as possible to assess the presence or absence of bats. 

Bat Activity Surveys require that buildings are monitored for approximately a two-hour period around either dawn or dusk. Ecologists will turn up armed with gadgets to detect the bat’s high- pitched squeaks as well as infra-red and  thermal imaging cameras to record the bat species and numbers. Ahern said: “Ecologists watch for how bats use a building: access points, which spaces they prefer and for what purposes - maternity roost, daytime snoozing spot for males and eating area.”

A report will then be prepared for you to submit to the local planning authority. Planning permission may then be granted subject to conditions for the protection of the bats. Planners will consider the conservation status of the bats recorded.  Some species are rarer than others. For instance, Bechstein’s bat is rare and found in southern England and south-east Wales. This means any proposals in these areas could be significant for the national population. Common pipistrelle are the most widespread bat species.

Cost of surveys

Surveys must be carried out by a licensed ecologist, usually CIEEM accredited. Preliminary Roost Assessments are advertised online for as little as £299  plus VAT for around one day’s work.  Be wary of bargain basement prices. Check the cheapest quotes are fixed fees and there aren’t any hidden costs. If you require a bat activity survey after the Phase 1 Survey, then the costs can escalate to thousands of pounds.

Bat mitigation measures

Where possible, building proposals should avoid affecting bats. For example, by leaving bat roosts in place. But if this isn’t possible, you will need to make alternative provision for bats spaces and structures. These measures will need to be set out in the ecologist’s survey report. They are likely to be picked up by planning officers who will make them a condition attached to your planning approval.

Providing alternative space can be as simple as putting bat boxes in trees on or near your plot. Other measures include bat tiles that provide built-in access points  into a roof  space. Or a bat loft, a separate area specifically modified for bats within the existing roof void. Brown long-eared bats, for example, need space to fly around before they emerge.  On rare occasions, standalone buildings may be required, primarily for use by bats.

If bats are shown to be present, you will need to have your ecologist apply to Natural England for a European Protected Species Licence on your behalf to ensure bats are safeguarded during any demotion or redevelopment of the building.  “The legal protection given to bats and their roosts, even when they are unoccupied, mean that only someone with a personal licence issued by Natural England can legally disturb a bat. Licenced persons tend to be ecologists, or sometimes arboriculturalists,” said Ahern.

Light sensitive

Bats are light sensitive. So, your ecologist can advise you on external lighting design and glazing design to prevent harm. Low-level or downward angled outside lighting can overcome this challenge. Any requirement for mitigation will depend on the species of bats that are found.

Tiny pipistrelle bats like tight spaces under roof tiles but can get entangled in the fibres of modern, breathable membranes. If you’re doing any roof work, be aware that certain materials, chemicals and wood treatments can be harmful to bats. Your ecologist will be able to advise on alternatives.

Bats can impact the timing of your project due to the limited season for surveys. They may also add some costs to your project, too and influence your design and choice of materials. It pays to plan ahead and consult a licensed ecologist  in the early planning project stages. Good ecologists get booked up quickly. Late summer is their busiest time. “We regularly receive phone calls from homeowners and their agent who have gone right through the planning process and a decision is held up because ecology wasn’t considered,” said Ahern.

If you are considering extending or altering your home, you may find some of these services useful: