Barn Conversions & Bat Surveys

Barn Conversions – An Introduction

Redeveloping a barn can be an incredibly rewarding experience. However, navigating through the planning process is seldom an easy task. One of the hurdles that must often be met is to undertake a bat survey. By their very nature, many old and derelict barns provide perfect conditions for roosting bats. Certain development works to these buildings therefore pose the threat of adversely affecting bats. If your Local Planning Authority suspects that the barn may support a bat roost, they will recommend that a bat survey is undertaken before planning permission can be granted.

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.

When considering the approval of your development proposals, the local planning authority and licensing agencies require information to determine the effects of the development on bats – to identify which species (if any) are present.

It is important to note that the requirement for a bat survey or indeed the presence of bats in your barn is very unlikely to prevent the development from going ahead. However, if bats are confirmed to be roosting within the building, then certain practices will need to be adopted to ensure that impacts to individual bats or the roost itself do not occur and that the bats can continue using the building following completion of works. This is achieved by the implementation of avoidance, mitigation and/ or precautionary measures.

Background to Bats

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 the water. Pipistrelles 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;
    A 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 apex’s 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 the barn, likely to be used by direct-access species
Horseshoe bats
Lesser horseshoe bats roosting adjacent to an open window

What Will be Involved?

Bat surveys generally consist of two phases, a daytime inspection and, if evidence of, or potential for, bats are 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 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 the 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.

To summarise, the objective of a bat survey will be 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.

Top Tips

Plan Ahead – Ecology is a highly seasonal It is often the case that prospective developers leave the ecology element of their planning application to the last minute, only to find that they have missed the window for undertaking stage 2 bat activity surveys. Their project be put on hold for up to seven months until late April/ early May.

  • Instruct a Reputable Consultancy – If your barn development requires a bat survey, you must instruct an experienced and licensed bat surveyor to undertake the Preliminary Roost Assessment. Non-licensed surveyors run the risk of breaking the law by entering bat roosts and disturbing bats. Not only will this eventually render the results of the survey null and void, but it could also lead to prosecution by the respective statutory body (Natural England in England and Natural Resources Wales in Wales). Acer Ecology’s licensed bat workers are experienced in undertaking every stage of bat surveys in a timely, pragmatic and cost-effective manner.
  • Prepare to be Flexible with your Design Plan – The types of bats that inhabit barns often require reasonable amounts of space within which to roost (i.e. void-dwelling and direct access species). It may be necessary to set aside certain areas of the barn for use as dedicated bat roosts following completion of renovation works. It is therefore important to remain relatively flexible with the design proposals so that any eventualities can be incorporated into architectural plans without lengthy and potentially costly delays.

Possible Outcomes

Depending on the nature of the bat roost and the proposed development works, the outcome of your bat survey could range from minor precautionary measures associated with the timing of works to like-for-like compensatory mitigation. The type of mitigation for roosting bats within barns depends on several factors: the species of bat, the functionality and ecological significance of the roost, and the development proposals. If your barn is confirmed as containing a bat roost, then it will be necessary to apply for a development licence from the relevant statutory authority (Natural England in England or Natural Resources Wales in Wales).

For a full guide to bat mitigation, check out our page here.

How We Can Help You

The fully licensed ecologists at Acer Ecology are experienced in undertaking bat surveys, European Protected Species Licensing, and the creation and implementation of mitigation. You can find past examples of our barn conversion work and other project examples here.

We operate across the West Midlands, South-West and Wales, offering a friendly, pragmatic and timely service that aims to guide your development smoothly through the planning process.

For more information, please call us on 02920 650331, or email