Bats and BuildingsBats and the Built Environment series

Guidance for built environment professionals,consultants, building owners and managers onthe conservation actions to promote and cater

for bats in buildings.

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Bat Conservation Trust

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Why do bats roost inbuildings?About half of the bat species in the world useholes in trees for roosting. The other half useeither caves or cavities, but also buildings. Infact, bats and people have been sharingdwellings for thousands of years. As naturalroosting sites have become scarce due todevelopment and land use change, so thenumber of artificial roost sites has increased inthe form of houses, bridges, mines, barns, ice-houses, etc. These man-made roosts can providestable micro-climates for the bats.

Loss of natural roosts has increased theimportance of man-made structures for bats tothe point that artificial roosts are becomingessential in the survival of many bat species.However even these man-made roosts are nowunder threat; demolition of old buildings,renovations, changes in use, artificial lightingand the move towards air-tight buildings, allhave implications for bat populations usingbuildings.

Protection and the lawIn the UK, due to the decline in bat numbers inthe last century, all species of bat are protected bythe Wildlife & Countryside Act (1981) as amended,Countryside and Rights of Way Act (2000) and theConservation of Habitats and Species Regulations(2010). This makes it illegal to deliberately orrecklessly kill, injure, capture or disturb bats,obstruct access to bat roosts or damage or destroybat roosts, whether occupied or not.

Having bats does not mean that building work,roof repairs, pest control or timber treatmentcannot take place. However, if any work is goingto alter the roost or access space an EPS licencewill be needed. You should consult your localStatutory Nature Conservation Organisation(SNCO) via the Bat Conservation Trust Helpline,before work starts and follow their advice onhow to proceed. In many cases they will send atrained licensed volunteer bat worker to inspectyour roost and provide advice, free of charge. Ifthe work is subject to planning consent anecological consultant should be employed.

To avoid delays, allow sufficient time ahead ofthe work to allow the SNCO to comment.

Which bats roost in buildings?All the UK bat species have been known to usebuildings but some species are more buildingreliant than others. Different bat species selectdifferent types of roosts in buildings since theylook for sites comparable to those chosen innatural habitats. Bats that use buildings cangenerally be divided into four categories,although there is regional variation and somespecies can occupy more than one category:

1. Crevice-dwelling bats (which tend to behidden from view) such as the commonpipistrelle, soprano pipistrelle, Nathusius’pipistrelle, Brandt's bat and whiskered bat

2. Roof-void dwelling bats (that may be visibleon roof timbers) are serotine, Leisler's bat,Daubenton's bat and barbastelle

3. Bats that need flight space in certain typesof roost are Natterer's bat, and brown andgrey long-eared bat

4. Bats that need flight space and flyingaccess into the roost are greater horseshoeand lesser horseshoe bat

Bats and Buildings

Bats are biodiversity indicators. Having a batroost in your building or surrounding area is

a sign of a healthy green environment.Making space for bats is an important

conservation action.

Natterer’s bat in brick work

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Please note: Information in this leaflet is primarily aimed at enhancement and does not replace the need for mitigation as part of the licensing process.

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Where in the building?In buildings a range of possible roostingopportunities exist that mimic those found inthe natural environment. Crevice-like or tree-cavity type spaces include those found in bothmodern and traditional houses such as behindfascia and barge boarding, spaces beneath roof

tiles, wall coatings, hollow mortice joints, raingutters and chimneys. Cave-like spaces includeattics and cellars that are dark, exhibiting stabletemperatures and humidity. These spaces may befound in a range of buildings including barnsand other farm buildings, historic buildings,castles, churches and terraced houses.

Bat signs: Bats do not make nests or cause structuraldamage. The most obvious sign of their presenceis droppings but even these can be hard to find.Bat droppings consist largely of insect remainsand crumble easily between your fingers to apowder of semi-shiny fragments. Rodentdroppings are smooth and plastic, quicklybecoming hard. They cannot be crumbled. Batdroppings are frequently mistaken for mousedroppings, so do the ‘crumble test’.

Bat droppings do not present any knownhealth hazards in the UK. They can be swept up

safely to use as an excellent fertilizer in thegarden.

Large accumulations may reflect use over anumber of years rather than large numbers ofbats at any one time.

Droppings may not always be readily visible ina loft. Other signs to look for are grease markson the rafters, urine splashes, cobweb freecorners, or insect remains from a feeding perch.

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1 Barge board2 Roofing felt3 Roof joists4 Ridge tiles5 Soffit6 Attic7 Lead flashing8 Dormer window9 Coping stones10 Gable end11 Valley12 Broken tiles13 Space between downpipe14 Metal elements on balconies15 Sash window16 Loose mortar between bricks17 Quoins18 Wood cladding19 End tiles20 Fascia board21 Eaves22 Guttering23 Window sill24 Porch25 Hanging tiles26 Cellar

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Bats and the Built Environment series

Places that bats may use in buildings

does not replace the need for mitigation as part of the licensing process.

A pipistrelle can use a holethis size to enter a building

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When looking for bats or their signsmake sure not to disturb the roost!

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What do bats look for in a home?Like us, bats are looking for shelter that is clean(free of disease and parasites), comfortable(protected from the weather) and secure (safefrom predators and disturbance). However, batsalso have unique requirements and may live inseveral different roosts throughout the yeardepending on their seasonal needs. A number offactors are very important when consideringroosts for bats:

Temperature Temperature is very important to bats. Bats aredifferent to us in that they look for warm roostsin the summer and cool roosts in the winter.

Summer:Bats usually only have one young a year. Motherbats gather together and find somewhere warmto rear their young called a maternity roost.Males will form smaller roosts elsewhere thatare often cooler than the needs of the females.Generally maternity roosts should probably bebetween 30 and 40°C (keeping in mind that thelarger the number of bats the greater thetemperature gain from body heat). Also, somespecies have their own unique preferences andstudies have shown that even a 1.5°C differencemay influence bats to choose one building overanother. It is always best to provide a number ofdifferent options for bats so that they canchoose the right roosts and temperature basedon their needs.

Winter:British bats feed on insects which are scarce inthe winter. Bats have adapted to this seasonalscarcity by going into hibernation where theylower their body temperature to the ambienttemperature or just above. Hibernation roostsare often a cool space, generally between 0 and6°C, with high humidity. Horseshoe bats preferslightly warmer conditions of 6-10°C.

Aspect and orientation Summer maternity roosts in the northernhemisphere often have a southerly or westerlyaspect for maximum solar heating. Male roostsand hibernation sites typically have a northerlyaspect.

Creating roosts in buildings

General principles for creating newspaces for bats in buildingsThe advice below describes general principlesto consider when providing new spaces forbats. It does not provide sufficient informationfor mitigation when a roost is already present.Work on existing roosts should be covered byan EPS licence.

Access, size of roost space andstructure • Crevice-dwelling bats can crawl into their

roosts via small gaps in the range of 15 -20mm high by 20 – 50mm wide. The roostarea should maintain a crevice of thisapproximate size gap that the bats can roostbetween. The area this roost provision coverscan be small but about 1m2 would be usefulfor summer nursery roosts. The height of entrycan be from 2 - 7m.

• Roof-void dwelling bats require similardimensions to access the roost but typicallyneed timber joists or beams on which to roost.The height of entry can be from 2 - 7m.

• Bats needing a flying area require the sameaccess dimension as mentioned above, 15 -20mm (h) x 20-50mm (w) situated over 2m inheight. The roosting area should not be

Bats and Buildings

Lesser horseshoe bat roost in garage loft

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Please note: Information in this leaflet is primarily aimed at enhancement and does not replace the need for mitigation as part of the licensing process.

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trussed, to allow flight, and should ideally beabout 2.8m in height and 5m in length andwidth.

• Horseshoe bats need a larger access so thatthey can fly (instead of crawl) directly into theroost. Lesser horseshoe bats need an access of300mm (w) x 200mm (h), while greaterhorseshoe bats need 400mm (w) x 300mm (h).As above, the roosting area should not betrussed, to allow flight, and should ideally beabout 2.8m in height and 5m in length andwidth.

Materials and structure Materials for the roosts should be rough (forgrip), non-toxic or corrosive, with no risk ofentanglement. The materials should also havesuitable thermal properties that reduce 24 hourfluctuations but allow maximum thermal gainfor summer roosts.

LightingBats are nocturnal animals and are adapted tolow-light conditions. This means that most batspecies can find artificial lighting to be verydisturbing. Artificial lights shining on bat roosts,their access points and the flight paths awayfrom the roost must always be avoided.

If it is considered necessary to illuminate abuilding known to be used by roosting bats, thelights will need to be switched off at batemergence time and during peak bat activity

times. Or better still, it is usually straightforwardto ensure that the light does not fall on theroost access point or the flight line away fromthe roost used by bats. Celebratory lighting ofbuildings should be limited to special occasions.

Please see BCT’s specialist document on Batsand Lighting for more detailed information.

LandscapeIn addition to the building requirements, it isimportant to provide the correct planting andlandscape features to attract bats in the firstplace. Proximity to vegetation, linear featuressuch as hedges and tree-lines, and access towater are all important.

Bats use linear features such as hedgerows,tree lines, and waterways as commutingpathways from the roost to foraging areas. Thevegetation not only acts as cover from potentialpredators and the weather, but also provides

structure for acoustic orientationand navigation and potential forfeeding on the insects found there.

Maintaining or creating goodforaging areas for bats meansestablishing areas that attractinsects, especially nocturnalinsects. These habitat featuresinclude rivers, ponds, unimprovedgrassland, ancient semi-naturalwoodland and hedgerows plantedwith native vegetation. See BCT’sEncouraging Bats document andthe Landscaping for Bats documentfor more information.

Bats and the Built Environment series

Roof reconstruction

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Example of good bat habitat©An

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Maintenance, repairs andalterations Bats are in an area that may be affected bybuilding works:Having bats does not mean that building work,roof repairs, pest control or timber treatmentcannot take place. However, you should consultyour local Statutory Nature ConservationOrganisation (SNCO) before work starts andfollow their advice on how to proceed. In manycases they will send a trained licensed volunteerbat worker to inspect your roost and provideadvice, free of charge.

It is important to allow sufficient time aheadof the work to allow the SNCO to comment.

Finding bats during building works:It is always important to keep in mind thepossibility of finding bats when doing any workto buildings. If bats are found during works, thework should stop and your local SNCO should beconsulted immediately.

Timing Building works should avoid the times of yearwhen bats are most vulnerable to disturbance.The summer months, when bats are in maternityroosts, and the winter months, when bats arehibernating, should be avoided. Typically earlyspring and autumn months are the best times todo work that may affect bats but it is alwaysbest to consult your local SNCO for advice.

Insulation

Loft insulationAlmost all UK bat species have been foundroosting in roofs. Any work that you carry out inyour roof void that has the potential to affect batsor their roost should be carried out only followingadvice from the SNCO. To avoid disturbance, worksshould only be carried out when bats are absentwhich will depend on the type of roost presentbut during April or between September to Octoberare likely to be the best times.

When installing insulation it is important toretain the bat access points to the roost. It isadvised to pare back the insulation a minimum of10cm from the eaves (this also helps to maintainbuilding ventilation). Spray insulation is notrecommended since access points cannot be easilyretained and due to the possible effect of thefumes on bats.

Cavity wall insulationBats are known to roost in cavity walls duringall seasons. The degree of importance for anyone species in each season is difficult to discerndue to the inaccessibility of the structure. Aconcern about the carbon footprint of housingstock has led to an emphasis on having cavitywalls insulated. To avoid entombing bats incavity walls it is advised to begin insulation fromthe bottom of the cavity wall and work upwards,thus giving any bats still remaining in the wall achance to wake and escape. If possible, a gap atthe top of the cavity wall should be left for bats.Check with your installer if this is appropriate.

If this is a known roost, access points and agap for the roost must be retained and the workmust not be done between 1 November and the

Bats and Buildings

By taking bats into account prior tostarting work, you will:• Minimise any costs and delays• Help to avoid disturbing bats or their

roosts, which means you will beavoiding the risk of prosecution andhelping to conserve an importantprotected species.

Serotine house roost

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Please note: Information in this leaflet is primarily aimed at enhancement and does not replace the need for mitigation as part of the licensing process.

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end of March, in case bats are hibernating in thewall. However, it is best to consult your SNCO,via the Bat Conservation Trust Helpline, foradvice.

Demolition The demolition of buildings is a major threat tobat species that use them. This is especially truefor demolitions where they are not part of aplanning application. Where this occurs an S80demolition notice is completed by the applicantand an S81 issued by a Building Control Officerat the local authority. In most cases the S80form supplied by the local authority does notinclude a question on protected species andtherefore it would seem likely that in manycases the presence of bats could be overlooked.

If there is a suspicion or likelihood that bats usea structure then it should be surveyed by anecologist prior to demolition as the CountrysideRight of Way Act and otherlegislation still applies.

BCT is working with theAssociation of LocalGovernment Ecologists (ALGE),the Chartered Institute ofBuilding (CIoB), CCW andothers to address this matterand raise awareness of localauthority duty in this situation.

Bats in newbuildingsThe move towards low and zerocarbon buildings places greatemphasis on building structuresthat are air-tight. Air-tightbuildings will not have the access and crevicesnormally used by building-reliant species such asbats and birds. In more traditional designs thatuse weather boarding/wood cladding, there maybe potential for some crevice dwellers (perhapsparticularly pipistrelles, Brandt’s bat andwhiskered bats) to find roosts. However, unlesspositive, proactive steps are taken, there isconcern that future housing stock will hold nopotential for bat roosts for several species.

However, it is possible to design into thefabric of the building ready-made or bespokespaces for bats that still maintain theairtightness (U-value) of the building. Pleaseconsult the RIBA Publication Biodiversity for Lowand Zero Carbon Buildings for more information.

The Bats and BuiltEnvironment leaflet seriesBats in Buildings is the first volume in a series ofBuilt Environment guidance leaflets that can befound at www.bats.org.uk. Other volumes willinclude guidance on Lighting, Insulation,Landscaping, Pest Control, Wind Turbines andRoads.

Bats and the Built Environment series

Habibat

Norfolk bat brick

Kent bat box

Schwegler bat box

does not replace the need for mitigation as part of the licensing process.

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enhancing homes for bats

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ResourcesFor more detailed information,please consult the followingresources:• Bats in Traditional Buildings,2009. English Heritage, NationalTrust and Natural England• Dr Carol Williams, 2010.Biodiversity for Low and ZeroCarbon Buildings: A TechnicalGuide for New Build, RIBAPublishing, London• Roost, the BatRoost Replacementand Enhancement Resource:http://roost.bats.org.uk

About the Bat Conservation TrustThe Bat Conservation Trust’s (BCT) vision is a world where bats and people thrive together in harmony.Your help can make a difference! Become a member of BCT today and help us to ensure futuregenerations can enjoy these amazing mammals.

You can join online or contact us on the details below. We can also provide details of your local batgroup.

Bat Conservation Trust National Bat Helpline: 0845 1300 228 www.bats.org.ukQuadrant House, 250 Kennington Lane, London SE11 5LD.enquiries@bats.org.uk

The Bat Conservation Trust is a registered charity, number England and Wales 1012361, Scotland SC040116. Company limited by guarantee number 2712823.

January 2012

Bat Conservation Trust

Leisler's bat on brick work

Brown long-eared bats in roof corner

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