Usually not. Most London loft conversions go ahead without a bat survey, because most London roofs are not likely to hold bats. You need one when there is a reasonable likelihood that bats are roosting in the roof and the work would affect them: typically an older house near a park, woodland, a river, a canal or a reservoir, with hanging tiles, gaps under the tiles or old lead flashing. The first step is a daytime roost assessment by an ecologist. If that finds roost potential, dusk emergence surveys follow, and those can only be done between May and September. A licensed ecologist does all of this, not us.
On this page
- Why do bats matter for a loft conversion?
- Does a permitted development loft still need to think about bats?
- When does a London council ask for a bat survey?
- What does the survey involve, and when can it be done?
- What happens if bats are found?
- What do our drawings do, and what does the ecologist do?
- Frequently asked questions
Why do bats matter for a loft conversion?
Every bat species in Britain is a European protected species. Under regulation 43 of the Conservation of Habitats and Species Regulations 2017, it is an offence to deliberately kill, injure or disturb a bat, and an offence to damage or destroy a breeding site or resting place. That last offence does not need intent, and Natural England's advice notes a roost stays protected even when the bats are away. The penalty is up to six months in prison, a fine, or both.
A loft conversion opens the roof: new dormers or a mansard, replaced tiles, new rafters, insulation pushed into the eaves. Those are exactly the places bats roost in a house. Natural England's standing advice lists the signs: uneven tiles, large roof timbers, cracks and small openings, and hanging tiles or timber cladding, especially on south-facing walls, near woodland or water and away from bright lighting.
Does a permitted development loft still need to think about bats?
Yes. Permitted development removes the need to apply for planning permission. It does not remove the wildlife law, which applies to anyone doing the work. With no application there is no council to ask for a survey, so the decision falls to you and your builder. If there are signs of bats, stop and ask an ecologist before the roof is opened.
Our loft conversion permitted development guide explains when a loft needs no application; this page is about what applies either way.
When does a London council ask for a bat survey?
The national test comes from Government Circular 06/2005, paragraph 99, still published on GOV.UK. Councils should not require protected species surveys unless there is a reasonable likelihood of the species being present and affected. Where there is, the survey should be done before permission is granted, not left to a condition, except in exceptional circumstances. So a survey the council needs is a survey you need before your application can be decided.
London councils turn "reasonable likelihood" into triggers on their validation lists. Kensington and Chelsea's submission requirements name work to older buildings and roof spaces, then list:
- buildings with wooden cladding or hanging tiles within 200 m of woodland or water;
- pre-1960 buildings within 200 m of woodland or water;
- pre-1919 buildings within 400 m of woodland or water.
That last line matters in London, because so much of the housing is Victorian or Edwardian. Where a council uses triggers like these, a terrace within a few streets of the Thames, a canal, a reservoir or a wooded park could fall within them.
Richmond's validation checklist, adopted in February 2026, goes further for a borough full of parks and river frontage. It says a preliminary ecological appraisal may be needed, including on householder applications depending on the extent of the work, where protected species are likely on or next to the site. Where only bats or nesting birds are likely to be affected, a preliminary roost assessment alone may be enough.
What does the survey involve, and when can it be done?
There are two stages.
Preliminary roost assessment. A daytime visit by an ecologist who inspects the roof outside and the loft inside for droppings, staining, feeding remains and gaps bats could use. If it finds negligible potential, the process usually ends there, with a short report you can submit. The daytime inspection is generally not tied to the summer season in the way the next stage is, but ask your ecologist about timing.
Emergence surveys. If the roof has potential, ecologists watch it at dusk to see whether bats come out. Under the Bat Conservation Trust's 2023 good practice guidelines, these surveys run between May and September, with mid-May to August the optimal period for maternity roosts, and fewer can be done in bad weather. The number of visits depends on how much potential the roof has.
The season is what catches people out. A bat survey report published on GOV.UK records inspections on 31 August and 14 September 2023, then 14 May and 4 June 2024: a survey started late in one season and finished in the next. If your loft is likely to need emergence surveys, book the ecologist in winter or early spring, not in August.
What happens if bats are found?
Finding bats does not usually stop a loft conversion. It changes how and when the work is done. The ecologist designs mitigation, such as keeping a roost space in the eaves, fitting bat access tiles, or timing roof works to avoid the months the roost is in use. Where a roost would be damaged or destroyed, the work needs a bat mitigation licence from Natural England, which the ecologist applies for. Natural England's advice is that councils must be confident a licence is likely to be granted before they grant permission.
The August 2026 National Planning Policy Framework also asks development to include features that support species such as swifts, bats and hedgehogs, so some councils will ask for a bat box or swift brick even where no roost is found.
What do our drawings do, and what does the ecologist do?
We do not carry out bat surveys or ecological reports, and we do not hold a bat licence. A licensed ecologist does that work.
Our planning, building regulations and structural package, from £1,395, gives the ecologist and the council the drawings they assess against: existing and proposed roof plans, elevations and sections showing which slopes are rebuilt, where dormers cut in and what happens at the eaves. If the ecologist asks for a roost void, access tiles or a bat box, those can be shown on the planning and building regulations drawings; the detail and any cost of that is confirmed at the quote stage. Building control's fire and structural questions for the same loft are covered in our loft fire safety guide.
The reports we sell, each with its price, are listed on our planning reports page.
Frequently asked questions
Can I check my own loft for bats? You can look for droppings on the loft floor or insulation and watch the roof at dusk in summer. Do not disturb anything you find. If you see signs, the next step is an ecologist, not your builder.
Does my builder need to know? Yes. The offence falls on whoever damages the roost. Give your builder the ecologist's report and any licence conditions before the roof is stripped.
Is a bat survey valid for ever? No. Natural England's advice is that surveys should be from the most recent appropriate season, so a survey several years old may need repeating.
Do I need a bat survey for a rear extension? Less often. A single-storey rear extension usually leaves the main roof alone. It is roof works, re-roofing and demolition that most often trigger a survey.
