Cornwall's old barns, stone cottages, slate roofs and wooded valleys make it a great place for bats, and that has a direct effect on building work. If you're planning a barn conversion, a loft conversion, a new roof, a demolition or a rebuild, you may need an ecology survey before work can start. Planning for this early can save months of delay. This guide explains when surveys are likely to be needed, how they work and how they fit into your timetable.
Why bats affect building projects
All bat species in the UK and their roosts are protected by law, mainly under the Conservation of Habitats and Species Regulations 2017 and the Wildlife and Countryside Act 1981. It's an offence to deliberately disturb, injure or kill bats, or to damage or destroy a roost, even when bats aren't present at the time. A roost can be as small as a gap under a ridge tile or behind a fascia board.
Because of this, Cornwall Council will often ask for an ecology survey with planning applications where bats could be affected, and the law applies to work that doesn't need planning permission too. Nesting birds are also protected while they're nesting, which can affect roof work, demolition and hedge or tree removal during the spring and summer.
Projects most likely to need a survey
You're more likely to need a bat survey if your project involves:
Barn conversions, especially in older stone or timber buildings.
Loft conversions or work that disturbs roof spaces, ridges, eaves or soffits.
Re-roofing or major roof alterations on older buildings.
Demolishing a building, including as part of a replacement dwelling.
Converting or extending buildings close to woodland, rivers or hedgerows.
Removing mature trees with features such as cracks, holes or ivy.
Signs of bats include droppings in lofts or on walls and windowsills, scratch or staining marks around small gaps, and bats seen flying near the building around dusk. Many roosts show no obvious signs at all, which is why a professional survey matters.
How bat surveys work
Bat surveys are carried out by qualified ecologists and usually follow published good practice guidelines. There are normally two stages:
Preliminary roost assessment. An ecologist inspects the building inside and out, looking for evidence of bats and features that could support roosting. This can be done at any time of year. If there's no evidence and low potential, this may be enough.
Presence or absence surveys. If the building has potential for roosting, or evidence is found, further surveys are carried out at dusk and dawn to watch for bats leaving or returning. These are only possible during the bat active season, generally between May and September.
The number of follow-up surveys depends on how much potential the building has. The ecologist's report sets out the findings and any recommendations for your planning application.
What happens if bats are found?
Finding bats doesn't usually stop a project, but it does shape how and when the work is done. Typical steps include:
A licence. Where a roost will be affected, a licence is usually needed from Natural England before work starts. Some lower-impact cases can be handled through a registered consultant under a class licence.
Mitigation. This can include timing works to avoid sensitive periods, providing a replacement roost, using bat access tiles or bat boxes, and leaving certain areas undisturbed.
Supervision. An ecologist may need to be present during certain tasks, such as stripping roof coverings.
Breathable roof membranes. Some modern membranes can be harmful to bats, so the ecologist may specify a suitable traditional underlay in roof spaces they use.
Your builder should follow the ecologist's method statement and licence conditions exactly.
Nesting birds and barn owls
Most wild birds are protected while nesting, so roof work, demolition, scaffolding and clearance may need to avoid the main nesting season, which broadly runs from early spring to late summer, unless a check confirms there are no active nests. Barn owls, which often use old Cornish barns, have extra legal protection. Swallows and house martins commonly nest in outbuildings and under eaves too. An ecologist can advise on timings and on providing new nesting places, such as swift bricks or owl boxes.
Building surveys into your timetable
The biggest risk with bats is timing. If a preliminary assessment in winter shows the need for further surveys, you may have to wait until May before they can be done, and a licence application only follows after that. To avoid delays:
Commission a preliminary roost assessment as early as possible, ideally before buying a barn or finalising designs.
Allow for the survey season and any licence in your programme.
Share ecology reports with your architect, engineer and builder at the design stage.
Check whether any planning conditions relate to ecology before work starts.
Our guides to planning permission in Cornwall, barn conversions in Cornwall and building in an AONB or conservation area cover the wider approvals process.
Bat survey FAQs
Do I need a bat survey for a loft conversion?
Not always. It depends on the age and type of roof, its location and any signs of bats. If there's a realistic chance of bats, an ecologist's assessment is the safest first step, and the council may ask for one with a planning application.
Can bat surveys be done in winter?
A preliminary roost assessment can be done at any time of year. Dusk and dawn surveys usually need to take place in the active season, generally May to September.
Will bats stop my barn conversion?
Rarely. In most cases, the work goes ahead with suitable mitigation, timing and, where needed, a licence.
Does a householder extension need Biodiversity Net Gain?
Householder applications are currently exempt from mandatory Biodiversity Net Gain, but protected species rules still apply, so surveys may still be needed.
Talk to us about your project
We work with ecologists and designers on barn conversions, renovations and new builds across Cornwall. Call Cornish Building Company on 01208 816991 or contact us to talk through your plans.
