How bat surveys delayed a single plot scheme by a year

If a preliminary roost assessment finds moderate or high suitability outside the survey season, your bat survey delayed planning problem has already happened and there is no way to buy your way out of it. Emergence and re-entry surveys can only be done when bats are active, broadly May to September. A report written in October puts the earliest survey seven months away and the earliest decision on a valid application somewhere after that.

What follows is an illustrative walkthrough, built from the way these schemes usually run rather than from any particular client's file. The figures are illustrative.

The site and the programme as drawn up

A self-builder buys a plot at the end of a village garden. On it sits a brick and tile outbuilding, a former stable of perhaps 40 m2, with a sagging roof and a gable open at the apex. The plan is a single dwelling, replacing the outbuilding, with a start on site the following spring.

The programme on the back of the purchase looks like this. Architect appointed in September, drawings in October, application submitted in November, decision in January, discharge of conditions in February, build starts in March. Eight weeks for a minor application feels comfortable and the plot was bought on that basis.

Nobody has looked at the roof.

What the roost assessment found

The architect, sensibly, commissions an ecologist before submission rather than after. A preliminary roost assessment is a daytime inspection of the building, inside and out, looking for bats, droppings, staining, feeding remains and the features bats use: gaps under ridge tiles, lifted flashing, mortice joints, cavity walls, soffit voids.

The ecologist inspects in early October and records the building as moderate suitability. No bats are seen and no droppings are found, but the roof has raised tiles along one slope, the gable is open, and the building sits on a woodland edge with a hedgerow running to it. Moderate is not a finding that bats are present. It is a finding that the building has features a roost could use and that presence cannot be ruled out from a daytime inspection.

That category matters because it sets the survey effort. Under the Bat Conservation Trust good practice guidelines, low suitability points to one emergence or re-entry survey, moderate to two, and high to three, spaced at least a couple of weeks apart and concentrated in the months when bats are using summer roosts. The difference between the categories is the single most consequential line in the report.

The season that had already closed

The good practice window for emergence surveys runs from May to September, with the most useful months in the middle of that. An assessment delivered in October means the first survey can be booked for May and the second for June, and the ecologist will not sign a report until both are done.

So the application does not go in during November. It goes in the following July at the earliest, assuming the surveys find nothing and the ecologist can write up promptly. A start on site moves from March to the autumn of the following year, or realistically to the spring after that once the winter is factored in.

The self-builder's first instinct is to submit anyway and deal with bats by condition. That does not work here. Where a protected species may be affected, the authority has to have the survey information before it determines the application, because it cannot assess the likely impact without it. Councils routinely refuse or hold applications that arrive with a preliminary assessment and a promise. A Protected Species Survey must be carried out by a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, and an AI-assisted draft is a starting point for that ecologist rather than a substitute for the survey.

Redesigning around the roost

The second instinct is better: change the scheme so the building does not need to come down.

The architect tests a conversion instead of a replacement. Retaining the walls and re-roofing, with the roof structure replaced in phases and bat access maintained at the gable, turns the proposal from destruction of a potential roost into alteration with mitigation. It does not remove the need for the surveys, because you still have to know what is there. It changes what happens if something is found.

On this plot the conversion does not work. The floor to ceiling height is too low for habitable rooms without lowering the slab, and lowering the slab undermines the footings. So the replacement dwelling stays, and the mitigation moves into the design: a bat access tile and a lined void in the new roof, a bat box on the retained boundary tree, and lighting specified to keep the hedgerow corridor dark.

That last point is the one most schemes get wrong. External lighting that washes a hedgerow used by foraging bats is an impact in its own right, and it is easy to condition and easy to breach.

The licence question

The surveys the following May and June record a single common pipistrelle emerging from under a ridge tile on the second visit. One bat, one night, no maternity colony. It is still a roost, and destroying it is an offence without a licence.

At that point three things happen in parallel. The ecologist writes the survey report with a mitigation strategy: timing of works outside the sensitive period, a soft strip under supervision, and the permanent replacement roost built into the new dwelling. The planning application is submitted with that report. And the authority, before granting permission, has to consider whether a licence from the statutory nature conservation body is likely to be granted, because permission that could never lawfully be implemented is not worth much.

The licence itself is applied for after permission is granted, not before, and for a straightforward single roost of a common species a registered consultant may be able to use a class licence rather than a full mitigation licence, which is faster. Either way the derogation tests have to be satisfied: there must be no satisfactory alternative, the action must be for a permitted purpose, and the favourable conservation status of the species must be maintained.

The revised programme and what it added

Set against the original programme, the scheme lost about twelve months. The direct survey cost was a fraction of that loss. The real cost was the year of finance, the plot sitting idle, and a build pushed into a worse season.

Three costs are worth separating, because self-builders tend to merge them:

1. The preliminary roost assessment, which is a half day inspection and a short report.
2. The emergence surveys, priced per visit with two surveyors on a building with several elevations, plus the report.
3. The licence work and the supervised soft strip, which only arise if a roost is confirmed.

Only the first is unavoidable on a building with any bat potential. The second follows from the category. The third follows from what the surveys find. Budgeting as though all three will happen, and being pleased when they do not, is the sane approach. The same logic drives the ecology line in a Green Belt stables scheme, where the constraint arrived from a different direction but had the same effect on the programme.

Avoiding the same delay

The order of operations is what saves the year, and it costs almost nothing to get right.

Commission the preliminary roost assessment before you exchange, or make the purchase conditional on it. An ecologist will walk a building and give you a category, and that category tells you whether your programme is a spring start or a following-year start. A Preliminary Ecological Appraisal at the same visit picks up the other seasonal constraints, from nesting birds to ponds within 500 m that bring great crested newts into the picture, each with its own window.

Then book the surveys before you need them. Ecologists fill their summer diaries in late winter, and a plot owner ringing round in June is joining a queue.

And read the report for the category, not the conclusion. Moderate suitability with no bats found is not good news. It is a bill for two survey visits and a place in next summer's diary.

This is general guidance, not legal advice, and this walkthrough is illustrative rather than an account of a real application. Check the position with your local planning authority and a licensed ecologist before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode on PlanScope to see which reports a plot like this is likely to need.