Bat Surveys of Traditional and Listed Buildings

Bat Surveys of Traditional and Listed Buildings

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Different Types of Traditional Building

Traditional buildings are present throughout Britain. They may comprise agricultural structures, period properties, listed buildings, churches and places of worship. They often form key contributions to an area’s sense of identity and character. Furthermore, they often distil a style of craftsmanship and building techniques that reflect the historical traditions of an area – many of which are no longer practised. Many traditional buildings are consequently considered to be of special value, and are protected by law from unauthorised alteration or neglect.

The statutory protection afforded to traditional buildings falls as either:

  • Listed – as being of architectural or historic interest; or
  • Scheduled – as a scheduled ancient monument.

This protection by law makes it a criminal offence, punishable by a fine or prison sentence, to carry out unauthorised work to a listed or scheduled structure. Together with the legal costs, you may also be required to reverse all unauthorised changes.

The first step when considering carrying out works to a traditional building or church, is to understand what is ‘significant’ about it. Whether the building has been relatively untouched for 400 years, features slates that were quarried on site, or has an exquisite plasterwork ceiling, its ‘significance’ is what makes the building special and important to the nation’s cultural heritage.

When looking to understand what makes your building significant, a useful starting point is to look at Conservation Principles, Policies and Guidance, published by Historic England. The guidance starts with six overarching principles that help to provide a framework for what conservation means, placing significance at the heart.

However, it is important to conserve these buildings not only for their inherent architectural or historical interest, but also because they provide vital roosts for most of the species of bat found in England and Wales.

Increasingly, one way of ensuring the long-term viability of these structures is for them to be converted, renovated, or refurbished. This process can potentially lead to conflicts with roosting bats.

Background to Bats & Their Roosting Preferences

There are 17 species of bats living here in the UK.

That’s almost a quarter of our resident mammals!

All of the British bat species are insectivorous and hunt using echolocation, which is inaudible to human ears.

Though they may rouse on warmer days to search for food and water on milder days, bats typically emerge from hibernation in March/ April. After building up fat reserves in the Spring, females move to their maternity roosts in June, and the young (pups) are born in between mid-June and July. Later in the year, bats gather at swarming sites where mating occurs. The males and females then build up their fat reserves ready for hibernation in November/ December. The females store the sperm over winter ready for the following June.

During the night, they forage for invertebrates, either in the air or gleaned from vegetation and the surface of water. Pipistrelle’s can eat around 3000 midges per night! However, once dawn breaks, bats must return to their roosts, as they are vulnerable to predation and less effective at hunting.

Different bats require different types of roosts:

  • Crevice-dwelling bats (such as Pipistrellus species and smaller Myotis species such as Brandt’s and whiskered bats) like to feel securely tucked away behind or within the features of a barn. Such features include beneath raised tiles, behind raised fascia and bargeboards, within crevices in masonry, between timber joints, inside window lintels, and under cladding and flashing;
Typical feature, likely to be used by crevice-dwelling bats
Common pipistrelle bat roosting within a mortise joint in a barn’s roof structure
  • Roof void-dwelling bats (such as long-eared species and large myotis bats such as Natterer’s bat) require open voids within which to roost. Typical features include the open apexes of barns, roof voids, underground structures and soffit boxes. Species like long-eared bats will often cluster together at the ridge of these features if they are present, and may be relatively conspicuous to spot. These types of bats may access the voids either by directly flying into them, or by crawling through crevices; or
Typical open, uncluttered roof space, likely to be used by void dwelling bats
Two brown long-eared bats roosting on a purlin in a void
  • Direct access species include lesser and greater horseshoe bats, which require a large access point and large roost space within which to hang up on the underside of features. Indeed, horseshoe bats are the only UK bat species that enact the stereotypical bat ‘pose’ of hanging upside down with wings folded around them. If you spot a small plum or pear-shaped object hanging from the roof of your barn, you may be looking at a horseshoe bat!
Clear access point into barn, likely to be used by direct-access species
Horseshoe bats
Lesser horseshoe bats roosting adjacent to an open window

Because of the variations in roosting requirements for different bat species, many modern buildings lack the features that can be utilised by bats. Furthermore, changes to modern agriculture, forestry and general urban development has reduced the number of natural bat roost sites in the wider landscape (such as in trees or subterranean features). The result of this change is that the opportunities provided by traditional buildings and churches are becoming ever-more appealing to bats. Furthermore, the typical surroundings of many traditional buildings (parkland, mature gardens, farmland, lakes and woodlands) provide optimal foraging and commuting habitat for roosting bats.

Roost Sites

The selection of potential roosting sites depends on several factors. A building’s suitability from a bat perspective depends on the structure, microclimate, level of disturbance (including lighting), geographic location and ecological setting. The ecological niche of the bat also plays a fundamental role. Bats are long-lived animals with good memories, often making them faithful to particular roosts when there are a high number of suitable alternatives in proximity to it.

Because of this, bats become well-acquainted to several suitable roosting structures within their home range. Depending on the nature of the roost, they may visit them regularly or occasionally. The function of the roost will vary depending on the season:

  • After emerging from hibernation in March/ April, individual bats will utilise roosts in small numbers for incidental use while foraging on warmer nights.
  • After building up fat reserves in the Spring, females move to their maternity roosts in June, and the young (pups) are born in between mid-June and July. These maternity roosts typically support the highest numbers of bats and are afforded the highest level ecological significance.
  • A large maternity roost may also support a satellite roost, which is made up by smaller numbers of breeding females in proximity to the main colony. These maternity roosts begin to break up during late July/ August, when the young start flying independently.
  • The onset of Autumn sees the beginning of mating activity, whereby bats gather at swarming roosts where mating occurs. The males and females then build up their fat reserves ready for hibernation in November/ December.
  • Sites where bats hibernate also comprise a distinct type of roost – a hibernacula.
  • Several other types of transitory roost also exist, including feeding perches and night roosts.

With this in mind, it is important to remember that an absence of bats at any given time, does not mean that the roost is no longer being used. Although the very nature of buildings provides permanent security for bats, the ever-present prospect of development means that demolitions, unsympathetic conversions, obsolescence, traditional skills shortages, and greater regulatory demands all pose the threat of destroying or damaging bat roosts.

Typical Works That May Affect Roosting Bats, and Appropriate Mitigation

Impacts to roosting bats can be broadly split into three categories:

  • Modification of the roost (including obstruction of access); and
  • Indirect impacts to roosting bats, including those associated to lighting, noise and vibration.
  • Death of, or direct injury/ disturbance to roosting bats;

Reducing the size of an area that is already being used by roosting bats can risk the ecological functionality and future viability of the roost. In tall traditional buildings (such as barns and churches), it is possible for bats to utilise the roofing timbers for roosting, while people occupy the areas below as usual (provided that conditions within the building do not vary significantly (e.g. large temperature fluctuations, or lighting being directed upwards).

It is therefore important to plan carefully if you intend to build into a roost or segregate off a section of area being used by bats. Ideally, a void retained for bats should measure at least 2m in height from floor to ridge (preferable over 2.5m), and a length and width of at least 4m (preferable 5m).

A good option when planning to develop a group of buildings used by bats (for instance a farm) is to consider retaining one of the buildings that is currently used as a roost, both in its form and function. This option would still enable the other building(s) to be renovated where necessary (at the appropriate time of year), and the retained building would then provide perfect on-site mitigation for bats during the development of the other buildings. Ultimately, this option would preserve the traditional building itself and the functionality of the bat roost in its entirety.

Many types of work that are apparently less obtrusive but also pose threats to roosting bats include:

  • Removal, replacement, or blocking of fascia boards, bargeboards and/ or soffit boxes. Where changes to these features occur, efforts should be made to recreate them on the developed building by creating ‘crawling bat-access’, whereby the new exterior fascias, bargeboards and soffits around the building will be set off the face of the render/ masonry, thus creating small spaces underneath that allow bats to access and roost behind;
  • Works to crevices in timbers and masonry. Many species of bats habitually roost within the crevices often found between roofing timbers of traditional buildings, particularly mortise joints. Furthermore, the internal and external crevices found in many walls often provide deep crevices and access to internal cavities that can provide perfect habitats for roosting and hibernation. Therefore, any loss to these features during the conversion should be replicated.
  • Great care must be taken when any re-rendering or demolition is required, as this work runs the risk of crushing or entombing any bats that may be present at the time of works. No lighting should be directed towards them and where feasible, noise should be limited with extra insulation;
  • Works to underground sites that may be used by hibernating bats. Any works to these areas should seek to maintain the same conditions of temperature, humidity, darkness and air flow following completion of works;
  • Works to areas used for night roosting or as feeding perches (mainly open-sided buildings such as Dutch barns, stables, lean-to’s etc) should aim to retain easy access to the internal reaches at night, for instance by providing gaps over closed doors, or retaining partially open frontage;
  • Increases in artificial lighting, whether within the internal reaches of the building, or externally, can indirectly affect roosting bats, either by making internal roosting areas unsuitable, or by preventing commuting bats from travelling to and from the roosting location. Although some species of bats can tolerate a degree of artificial lighting, some species (such as horseshoe bats and long eared species) are highly light sensitive, and will actively avoid areas of lighting. It is therefore prudent to implement a sensitive lighting strategy for bats, which may include a dark corridor around some of the external elevations of the building.

In most cases, modifications and repairs to buildings can be made in such a way that bats continue to flourish, provided enough care, consideration and forward planning are given.

Bats and The Law

All UK species of bat are designated as ‘European Protected Species’. Their breeding sites or resting places (roosts) are fully protected under the Wildlife and Countryside Act 1981 (as amended) and the Conservation of Habitats and Species Regulations 2017.

In Britain, all bat species and their roosts are legally protected by both domestic and international legislation. It is an offence to:

  • Deliberately capture, injure or kill a bat;
  • Intentionally or recklessly disturb a bat in its roost or deliberately disturb a group of bats;
  • Damage or destroy a bat roosting place (even if bats are not occupying the roost at the time); and
  • Intentionally or recklessly obstruct access to a bat roost.

Works affecting bats are subject to licensing procedures by Natural England (NE) and Natural Resources Wales (NRW) respectively.

A method statement is obligatory if a licence is required. However, a licence will be unnecessary if the work can be organised in a way that avoids disturbing bats or damaging/ destroying their roosts.

Bat Surveys

Bat surveys generally consist of two phases, a daytime inspection and, if evidence of, or potential for, bats is found, activity surveys.

One of our bat surveyors carrying out a Preliminary Roost Assessment

The first stage comprises a Preliminary Roost Assessment, whereby a daytime internal/ external inspection is undertaken by a licensed bat ecologist. This element of the survey can be undertaken at any time of the year. The ecologist will search all of the internal voids, attics and basements, as well as the external elevations of the building to search for evidence of bats and potential entry/ access points or roosting features – the results of which give an indication of the ‘potential’ of the barn to support roosting bats. It may therefore be necessary to carry out further (stage 2) surveys for bats, even if no direct evidence is found during the Preliminary Roost Assessment.

If no evidence is found and the building has negligible potential to support roosting bats, it would not be necessary to undertake any further survey work. However, if the Preliminary Roost Assessment identifies evidence of bats, or low, moderate or high potential for supporting them, then further (phase 2) activity surveys would be required in order to determine the exact species and numbers of bats, together with the roosting locations. This information enables an assessment of the roost and it’s subsequent ecological significance to be made.

Activity surveys are seasonally constrained and can only be undertaken from late April to mid-September (ideally May to August) during the period when bats occupy summer roost sites. At least one survey must be undertaken during the period from May to August.

The objectives of a bat survey are to:

  • Establish the presence/ likely absence of the bat roosts within trees and buildings;
  • Identify the activity of bats across the site and key commuting and foraging routes; and
  • Recommend ecological mitigation and enhancement where required.

Managing Visitors and Bats

If your traditional building, whether it be an agricultural barn, a listed building or a church, receives visitors or the general public regularly, it is important to plan new visitor attractions or events so that they do not conflict with bat roosting areas, as far as is practically possible. If you have carried out a bat survey to identify where the roosting locations are within your traditional building, you should consider all of the potential impacts to that roost if activities are planned in proximity to them, any of which may effectively result in the law being broken.

In large barns, listed buildings, or churches, limited numbers of visitors may not be problematic to the function of the bat roost. Conversely, it is very unlikely that bats will have occupied very small sites that have always been regularly used by people. The potential for adverse impacts to bats lies between these two extremes.

Potential conflicts are understandably easier to manage in larger traditional buildings, where human activity may take place some distances from the roosting locations (for instance regular services in a church are unlikely to impact roosting bats high up in the roofing timbers, or in the attic void above). However, in smaller structures (whether it be a barn, listed building, church, ice house, cellar or stable), are more sensitive for obvious reasons. It may be possible to convert a portion of the structure (for instance the ground floor of a stable), while leaving the bat roost within the roof structure unaffected. Where this segregation is not an option however, such as ice houses, vaults, or areas of public interest within or directly adjacent to the bat roost areas, disturbance will be very hard to avoid without adopting appropriate measures.

One commonly used effective approach is to allow public access during certain period of the year only. As we have set out earlier in this article, bats are highly influenced by seasonal chances – regularly moving from roost to roost for certain periods of the year. Therefore, it may be possible to only provide access to your traditional building during the summer months (if the structure comprises a hibernacula), or vice versa – avoiding public access during the core maternity season for bats (roughly from mid-June – late July inclusive).

Top Tips

Here we set out several top tips to consider when planning works to your traditional building, and deciding whether it requires a bat survey:


  • Start with the assumption that bats are present in a traditional building or the surrounding site. Once a bat survey has been undertaken, it may be possible to rule this situation out, but any works undertaken in the absence of this information will be deemed reckless at best and potentially intentional if any roosting bats are affected by the proposed works;
  • Plan ahead and be proactive where possible to towards bats. This should comprise organising surveys, developing management plans, improving surrounding habitats, or adding extra roosting places where practical. Acquiring planning consent can be a time consuming process at the best of times, but discovering roosting bats when works have already started can prove to be a both time consuming and costly;
  • Acknowledge that each site is different and needs to be assessed on a case-by-case basis to come to a conclusion that is both acceptable to the needs of the traditional building and the roosting bats;
  • Seek advice from the relevant statutory body (Natural England in England and Natural Resources Wales in Wales) at an early stage if any work or changes of use are likely to occur where bats are likely to be present;
  • Think ‘bat’ when any changes are made to the structure, whether major or minor;
  • Place a sign at the entrance to a known roost to warn anyone who may require access;
  • Consider whether surveillance will be beneficial. Monitoring via regular bat counts will help to determine whether the changes to the structure have had a detrimental effect on the bat colony. Local bat groups may be happy to assist here.


  • Allow works to be carried out in areas used by roosting bats without first confirming that the law is being complied with;
  • Pick up a bat with bare hands, nor allow other people to do so. A very low number of bats in Britain have contracted the rabies virus, and therefore anyone bitten by a bat should seek immediate medical care;
  • Assume that site workers or the general public have been informed about the presence of bats in a certain area of the structure;
  • Carry out unauthorised work to a listed building. This will constitute a criminal offence, punishable by a fine or a prison sentence. Furthermore, the local planning authority may demand that all unauthorised alterations are reversed; and
  • Carry out unauthorised work to a scheduled monument. This will constitute a criminal offence, punishable by a fine or a prison sentence.

For more information about bat surveys or any of our other ecological services call us on 029 2065 0331.