Managing Properties for Bats and People
Bats and people have been sharing dwellings for thousands of years. As cohabitees, they cause little or no trouble. Bats are clean in their habits and like to be left alone. This section looks at how to manage any property management issues that may arise.
Cohabiting with bats
Bats do not gnaw at wood or wiring or enlarge entry points and do not bring any materials into their roosts. However, if their droppings and urine are allowed to accumulate this can create a smell or staining. A bat specialist can help to remedy such situations.
At dusk or after dark, or even on hot days, a bat may occasionally accidentally stray into areas of buildings not used for roosting and this could trigger security alarms where fitted. The web section What to do if you find a bat offers advice.
A building or property management plan put together with advice from a bat specialist can detail how to integrate the use of the property and bat protection. The management plan can specify levels of visitor numbers, noise and such like that need to be avoided, and also monitoring. The impact on bats and the appropriate mitigation will depend on the time of day and season. Bats should be monitored by a bat specialist before and after events to assess the impact on them.
All visits to bat roost areas by staff, residents, visitors or contractors must be planned and appropriate instruction given. Bat awareness training should be given to all staff and a log of all bat roosts kept up to date, along with a plan of what to do if/when bats are found.
Once bat roosting sites have been located, label them so that anyone who enters them in the future is made aware that there is a legally protected bat roost.
Droppings and urine, smells and staining
Bats flying around buildings may leave a scattering of droppings and urine on walls, floors and objects. Concentrated areas of droppings and urine can build up under roosts.
Droppings are largely made up of the indigestible exoskeleton of bats' insect prey with additional nitrogen compounds and a small percentage of fats and oils. They may cause small amounts of pitting, long-term staining, and etching to porous materials such as sensitive painted wall surfaces, stone, and wooden monuments and sculptures. Droppings act as a source of nutrients for bacterial and fungal decay, which can cause paint and gilding to detach from its plaster backing, causing permanent damage and loss.
Bat urine decays to form dilute ammonia and other compounds. This alkaline urine is chemically more aggressive than droppings. It causes spotting and etching of wooden, metal and painted surfaces leading to conservation issues.
The Historic England-supported Bats in Churches project’s Cleaning Guidelines For Churches With Bats provides detailed advice on looking after fittings and furnishings from woodwork to ceramics, as well as how to deal with bat droppings and urine.
When cleaning historic materials, you are strongly recommended to avoid the use of chemical cleaning products, including standard domestic products, as these may inadvertently cause more damage than the bat droppings and urine. Professional conservation advice will be needed on removing stains and scarring to ensure materials are not damaged.
Protecting sensitive surfaces
When bat roosts are identified within a traditional building, it is important to identify any potential risks to historic fabric vulnerable to damage. Advice should be sought from an accredited conservator and a bat specialist.
The easiest way to protect surfaces from damage by bat droppings or urine is to move the objects or furniture, or cover them with cloths or other breathable materials during the night. Plastic materials, including foam-backed carpets, should not be used as covers, as they may create a moist microclimate.
Varnishes and wax polishes (including natural organic coatings such as beeswax or microcrystalline wax) offer little protection for metal, wood and tiles. They are only acceptable for surfaces of low artistic and historic interest, and you will need to contact a conservator to ensure such treatments will not be harmful to your objects. Wax polishes also require regular application.
The Bats in Churches project is looking at measures such as banners, curtains or canopies to deter bats or protect surfaces. Such measures need to be considered very carefully. They may also be detrimental to the conservation of building features like wall paintings. The bat specialist consultant and conservator need to collaborate to design mutually acceptable solutions.
In extreme cases, it may be possible for a bat specialist consultant to apply for a licence allowing the legal exclusion of bats.
Cleaning-up bat droppings and urine
There is no evidence that bat droppings or urine have caused disease or harm in the UK but when cleaning up do wear gloves and a dust mask, and wash hands afterwards. The Bat Conservation Trust provides further guidance.
There should be no lighting in areas with bats. If it is necessary, you will need advice from a bat specialist. Solutions may include installing low-level lighting to avoid spill onto bat habitats or using a light timer in areas where bats may be roosting nearby. Because underground sites are often used by bats in winter, a bat specialist may advise restricting the use of lights to the summer months only.
Lighting inside a roost site should be avoided wherever possible. If lighting is necessary, for example, if people also use the same area, you should take advice from a bat specialist. Examples of measures you might be advised to take to minimise internal lights include:
- Clearly marking light switches to remind people about limited access, and to switch lights off
- Adding a warning light (by the fire alarm panel, for instance) to alert staff if lights are left on accidentally
- Checking there are no additional light sources added to the roost area, or lights to illuminate roof timbers
It is best to avoid two-way switches in bat roosts that turn lights on/off in more than one place, so as to reduce the likelihood of a light being left on accidentally. You should also avoid having a single light switch that turns on the lights in more than one area of a building, including the bat-roosting area. Where you do have these - for instance, in linked cellars or roof voids - you can easily remedy this by removing the bulbs from the sockets in the roosting area.
Check that any ceiling lights in upper-floor rooms do not leak their light into the roof void where bats roost. Where it occurs, you can stop this by shading the light from above with a light-proof and heat-resistant box or upturned metal bucket.
The first thing to remember with all exterior lighting is to only use it where it is absolutely necessary. There are a multitude of benefits to planning a sensitive lighting scheme, from saving energy to avoiding disturbing people, as well as protecting bats. Light at a roost exit potentially causes roost abandonment and can entomb the bats, which would constitute an offence. At the very least the light will interfere with the bats' emergence and feeding time, which has knock-on effects on adult fitness and juvenile growth rates (and therefore the population's survival). Lights along paths and roads can also disrupt bats’ flight lines.
The impact of lighting can often be reduced. A bat specialist can help with advice. In general, you should:
- Never have light pointing at bat roosts or flight paths
- Always avoid light with a blue-rich / UV content as this attracts insects from dark areas creating a ‘vacuum effect’ for light shy species and opening up light opportunistic predator species to predate on the bats
- Use the minimum light intensity possible to avoid spill, glare and reflectance onto important bat habitats
- Use low-level lighting (both height above ground and intensity) to avoid glare
- Check internal light isn’t spilling onto external habitats
- Lighting of ice houses and similar historic structures should be avoided. Ice houses are typically only used by bats for hibernation, however, so if you particularly want to accentuate it through lighting, you may be able to restrict this to the summer months. This should be done under the guidance of a bat specialist.
Further guidance is provided by the Institution of Lighting Professionals’ (ILP) and Bat Conservation Trust in their Guidance Note 8 Bats and Artificial Lighting (August 2023).
Security and alarms
Security boarding-up, grilles and lights
When planning security or anti-vandalism measures for buildings, cellars and tunnels which are used by bats, you will need a bat specialist.
Floodlighting may be needed (and insisted upon by insurance companies). This can affect bats as they emerge from their roosts, so you will need to take advice from a bat specialist consultant on installing lights at bat roost access sites.
For security, windows are commonly boarded up with chipboard panels as a cheap, temporary solution. Doors may be boarded up similarly or replaced with a solid steel door. As well as the risk of blocking access to bats or bats roosting behind them against window panes, such boards can also prevent adequate ventilation of the building and may quickly become targets for graffiti.
Instead of boards, you might be able to use a steel grille which would allow bat access, maintain ventilation and prevent graffiti. Even better for bats, horizontal bars with a minimum air space between bars of around 130 millimetres (or 150 millimetres for horsehoe bats). These would allow bats to fly through, yet keep people out. If there is a risk that people might climb the bars, fit vertical bars but allow a gap over the top of 130 millimetres. You might find that a combination of a solid panel (wood or metal) with horizontal bars over the top is a suitable solution at some sites, such as the entrance to a low tunnel. This combination may be used to exclude foxes and allow bats to hibernate in safety.
Bars need to be removable to allow human access when required and you can do this by making the grille into a hinged door or into a removable panel. By fitting the lock on the inside of the bars and in a protective steel cover, you can securely padlock the door or panel in a reasonably vandal-proof way.
It may help to prevent or curtail persistent vandalism if you were to erect a sign just inside the building, and visible through the bars, which stated, for instance, that the site contains nothing of value and that the bars are there to protect rare bats from disturbance.
Find more advice about:
- Securing buildings in Historic England's Vacant Historic Buildings guidance
- Managing underground sites for bats
Intruder and smoke alarms
At night, small numbers of bats may find their way from their roosts into rooms, or stray into buildings during the night and fly around. This behaviour is more common in July and August when juveniles are starting to fly. They may set off intruder alarms.
In most cases, small modifications will solve the problem. Some sensors can be set to be less sensitive, so that a passing bat will not trigger them but a human will. It may be possible to relocate the sensor where it is unlikely to detect movement from bats, such as nearer to floor level and away from corners. Another option could be to fit active infra-red twin beam sensors (or cable and programme existing sensors as a beam pair) so that both beams have to be tripped concurrently to trigger the alarm, and ensure they are arranged so a bat cannot do this. Always carry out a walk-test to confirm that sensors will be activated by human presence only. If these modifications are not possible, consider replacing the movement sensors with floor pressure pads on entry routes, magnetic contacts on access doors and vibration sensors on window frames.
Smoke sensors in rooms are less often affected by bats. However, each roof void section of a large or traditional building is likely to have its own smoke sensor on the ridge beam, which is where bats often roost. The extra roosting perch offered by some designs of sensor may result in bats actually hanging on the sensor.
Sensors require regular testing which may involve a technician entering the roof void and working close to the ridge where bats may be roosting. These inspections need to be scheduled so the bats are not disturbed.
A bat specialist can help you with sorting out problems.
Bat flaps, doors and shutters in roof void firewalls
Fire regulations require that long and large roof voids are divided up into shorter sections with fireproof walls usually of brick, breeze-block or similar. These prevent the spread of fire or smoke from one area to another through the roof void.
Bats will use all or most of a large roof void according to the time of year and conditions. A firewall would restrict this free movement and can make a roosting site unsuitable or inaccessible for bats. The fitting of the wall could cause disturbance to roosting bats, too. Get advice from a bat specialist before you fit any firewalls inside an area used by bats.
After taking advice from a bat specialist, it is possible to provide access for bats by building a bat door, flap or steel concertina shutter into the firewall. These can be set to automatically close in the event of a fire to make the fire barrier complete.
The bat consultant can advise on the size of the bat flap aperture for the relevant bat species.
Case study: Installing bat access in roof void firewalls
Fire doors had to be installed in the roof voids of National Trust buildings: Bradenham Manor, Claydon House, and cottages at Greys Court. Bat roost access within and exit points from the compartmentalised roof voids was maintained by adding vent tiles and shuttered hatches. Details are provided on the Bat Conservation Trust website.
Visitor attractions and events
New visitor attractions such as the opening up of servants' quarters or a stable for shelter in wet weather; or events such as concerts, fireworks, light installations, weddings and parties, need to be planned around the bats to ensure lighting, noise and heat does not disturb them. Noise and lights can affect emergence or disrupt foraging or flight lines. During summer, feeding times are reduced as the nights are short.
Every site is different. Each needs to be assessed by a bat specialist to work out the needs of the bats and how to integrate visitor access.
For example, at larger sites such as churches/chapels, large halls and large barns, bats may be roosting some distance from coming into contact with people and therefore the site may be able to cope with a certain amount of public access. This does depend on the species, the type of roost, the number of people and any provision currently made to protect bats on the site.
Regular church services, for instance, might continue with little evident adverse effect on bats roosting in the roof timbers, whereas holding a floodlit concert illuminating their roosting sites on a summer’s evening where female bats may have young would be likely to cause an impact.
On smaller sites, such as stables, cellars and ice houses, it may not be possible to have areas where bats aren’t present and therefore people can access without causing some disturbance. You may be able to get around this by only giving public access during the months bats aren’t present.
Monitoring by a bat specialist is critical in understanding whether there is an impact on the bats. Regular bat counts should indicate whether the level of activity is having any detrimental effect on a colony.
Your bat specialist should be able to advise on a management plan for the site. In this way, certain sensitive areas could be highlighted in the plan as 'no-go' areas for the public at certain times. The plan might set out lighting and heating levels and define acceptable noise levels. In planning events, you will need to make sure that:
- Roosts and entrances are kept in darkness and free from obstructions, and the main noise is kept as far away as possible. Research has shown that event lighting does deter bats from emerging. They wait until the event has finished and the lights are turned off. This delay in emergence means that the bats are not able to forage at the optimum time (when insect prey numbers peak), thus reducing their foraging efficiency. For lactating females, this delay could mean producing less milk and therefore less healthy young.
- In winter, any event is not close to any hibernating bats, and not in the same room. The warmth from the public, as well as the noise and lights, may arouse them, causing them to use up some of their limited, stored body-fat and reducing long-term fitness.
- Noise is limited. Whistles, shouts, claps instruments, cars (brakes, car doors, tyres on gravel) can disturb bats.
- Fireworks can disturb bats. Fireworks should not be scheduled to be set off at least one hour before their main emergence period (which is usually about sunset time). The fireworks should be positioned as far from the roost as possible.
Engaging audiences and outreach
Bats fascinate many people. Indeed, the public expects them to be present in places such as crypts, cellars and caves, and old buildings.
Bats can provide good publicity and raise the profile of a building, as well as wildlife interests. They can be used to draw visitors through evening guided bat walks, viewing CCTV in bat roosts (which will need to be licenced), and talks about bats.
Interpretation can help where areas have to be kept out of bounds or artefacts covered; and provide an opportunity to explain why bats are a protected species, what you are doing to conserve a traditional building and its contents, plus the building's role as a habitat. It also gives an insight into another side of the work of your staff.
The Bat Conservation Trust offers education and outreach resources. Local bat groups will also have a vast deal of knowledge to share on bats in your area.
Bats in Churches Project
Historic England is a partner in the National Lottery Heritage Fund project Bats in Churches along with Natural England, the Church of England, Historic England, the Bat Conservation Trust and the Churches Conservation Trust.
Experts and volunteers from across the natural and cultural conservation realms are working together to investigate and put in place practical solutions to the problems caused by bats in historic churches, and to help church communities to live alongside their bat populations.