Bats are amazing little creatures and so varied that their species numbers make up a fifth of all mammal species! They can be so tiny (like a bumblebee) or rather larger like a small dog. Most live in the tropics but they are very widespread globally only missing out the icy poles and a few isolated oceanic islands. Here in the UK though, we have less than 20 breeding species. All of these are nocturnal, small, feed on insects and all protected by law as they are endangered.

Bats help with the spread of seeds, pollination and pest control, and should be welcomed into our ever increasing urban landscape. Because the UK bats feed on insects, their foraging grounds tend to be linked to where insects do well, like hedgerows, unimproved pasture, meadows, native woodland and bodies of water but they can be found in all sorts of locations including city centres. Some species of bat can consume up to 3000 small insects (like gnats & midges) a night!


From an architecture and buildings point-of-view, a key consideration is that bats use existing spaces rather than build their own new nests. Over hundreds of years they have adapted to use our buildings rather than the reducing woodlands. They like roosting sites to be dark, undisturbed and of the right temperature for their purpose, of which many buildings offer better conditions than in nature. (Just like us, they prefer the comfort of our buildings). They use different roosting spots for shelter, to hibernate and to raise young. A difficult result of all this as an architect or building owner is that there are so many variants to consider. Depending upon the species, its needs, and if it is a maternal roost, a hibernating roost, a day roost or a group or individual bat etc, the roosting site will all need different conditions to suit each purpose. This is why an ecologist’s report and advice is the only real way forward to determine what you have got or not. Once a bat has found a good spot, it will likely return to it year after year as long as conditions remain favourable.

A relatively recent development of the building stock is the sealing up of gaps, eaves, windows and draughts. This is great from a heat-loss perspective but not so good for crevice-dwelling bats and other wildlife access.

Once a site is lost, it may struggle to find a replacement in time. Only a single young is born per year, so recovery from changes to roosting sites can also take many years to take place.

All UK Bats are endangered and they are protected by UK and EU laws, and are often referred to as an EPS or European Protected Species.

The protection under the UK Conservation of Habitats and Species Regulations act(s) basically state that it is an offence to kill, injure, take or sell any bat. It is also a separate offence to damage or destroy any place used by bats for shelter or as a breeding site, even if the bats are not present. It is also an offence to deliberately or recklessly disturb a bat in a way that would affect its ability to survive, breed or rear young, or affect the local distribution or abundance of the species. These protections come with up to an unlimited fine, 6 months imprisonment and items used in the offence (diggers, tools etc) may also be forfeited.

As you can see, this is a fairly broad and robust protection, so if you have bats in your loft, barn, cladding or outbuilding things look pretty damning on any development plans. However to carry out activities that would otherwise be illegal (eg to disturb/alter a bat roost) an EPS licence can be granted as long as the licensing authority (Natural England here in Devon) is satisfied. Not all works will require a licence, only if the bats will be disturbed or their conditions changed. Under advice from an ecologist, designs can be sometimes be altered or carried out in a manner to not harm bats and therefore proceed without a licence. Applying for a licence will take time, and an approved licence comes with a time limit so future planning is important.

Your building’s unique situation and design requirements will be assessed by your ecologist and they can advise on the design and any licensing needs. Typically on projects that require an ecologist, (loft conversions, demolitions, removal of roofing/cladding) they will carry out a survey or two, write a report and advise on any alterations or additions to the design. Most of the time, this is usually a few bat access slates or some additional nesting boxes, to provide mitigation or net gain, but sometimes greater measures are necessary involving leaving large areas undisturbed. In extreme cases for specially important roosting sites or rarer species, works of that nature may not be possible/plausible. Below are some old English Nature images illustrating some typical bat access solutions. English Nature is now part of Natural England, and even though the details are old, the principles haven’t changed that much and give an idea of what to expect.

Bat slate access

A preliminary inspection can be carried out any time of year and involves an internal and external assessment of the building(s) by an ecologist. This will determine if a it has potential for bat roosting and whether additional survey(s) are necessary. If no bat evidence is found, then a simple letter-based summary will satisfy the planning authority that works can take place without further action.

If there is good evidence of bat activity, droppings, scratches, access holes or actual bats, then typically a second and/or third survey will be necessary. The second survey is usually an ‘Emergence Survey’, where the ecologist monitors the building at dusk to record bats coming and going from the building. If it is only a low potential roosting site this is carried out between April and October (dependent on prevailing conditions). For buildings with more higher potential for bats or well founded evidence, a narrower window between May and August is typical. If it is a hibernation roost, then the survey is between November and April. If your building has the higher category of potential for bat roosting, two or three emergence surveys may be necessary, but this can all be determined at the preliminary assessment by the ecologist.

The yearly cycle for bats is summarised as:

Bats hibernate in the winter, occasionally rising (particularly smaller species) for feeding when mild.

*In the spring pregnant females gather in warmer maternity roosts in preparation for the young being born in the summer. During spring months non-mating singles and males roost in cooler spots either as small groups or as individuals.

*In the summer the young are born and fed.

By autumn the young are feeding independently and all bats are trying to put on weight for the winter.

* Survey seasons

Therefore as part of the early design process and information gathering stages it can be crucial to engage an ecologist to carry out their preliminary assessment so they can advise on any other necessary surveys needed between spring and autumn (Apr/May to Sep/Oct) and avoid delaying to the following year’s survey season.

Further advice can be found at the following sites:

The Bat Conservation Trust –

Government pages on bat protections and licences

There is also advice on the government website about using fungicides and insecticides in bat roosts. For example if you need to treat woodworm in a loft that bats use.