Preliminary roost assessment: what the categories mean

A preliminary roost assessment grades a building for its bat roost potential as negligible, low, moderate or high, and that category decides everything that follows. Negligible normally ends the matter. Low, moderate and high each trigger a rising number of emergence or re-entry surveys, and those can only be carried out between May and September. For a householder planning a loft conversion or a re-roof, the category returned in February is the difference between applying in March and applying in July.

Bats and their roosts are protected under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017. The protection applies to the roost whether or not bats are present at the time, which is why an empty loft in winter is not an answer.

What the assessment involves

An ecologist inspects the building inside and out. Roof voids are searched for droppings, urine staining, feeding remains and live bats. External elevations are checked from ground level, usually with binoculars, a high-powered torch and sometimes an endoscope for gaps that can be reached safely.

The surroundings matter as much as the building. A stone cottage beside a wooded stream with hedgerow connections scores differently from an identical cottage on a lit main road surrounded by hard standing. Bats commute along linear features, so hedges, treelines and watercourses within a few hundred metres are recorded.

The desk study sits alongside the inspection. Records from the local environmental records centre, any known roosts nearby and previous survey work on the site all feed into the grading.

The four categories

The survey effort in the right-hand column follows the good practice guidelines published by the Bat Conservation Trust, which ecologists apply as the professional standard. The guidelines are revised periodically, so the ecologist will confirm the effort current at the time of your assessment.

Evidence found during the inspection changes the picture immediately. A scatter of droppings on a roof timber, identified to species where possible, takes a building to confirmed roost status and moves the question from whether bats are present to what the roost is and how the works affect it.

Features surveyors look for in a roof

In the void, the list is short and specific. Droppings on rafters, joists, beams and the floor beneath ridge boards. Staining around gaps where bats squeeze in and out. Scratch marks on timber. Moth wings and other feeding remains below a perch. Live bats hanging in the ridge or tucked into mortise joints.

Externally, the features are gaps rather than objects. Lifted or slipped tiles, missing mortar at the verge, raised ridge tiles, gaps behind fascias and soffits, spaces under lead flashing at an abutment, and the cavity behind hanging tiles or weatherboarding.

Modern roofs with breathable membrane, sealed soffits and tight verges usually grade negligible or low. A 1900 slate roof with a bitumen felt underlay and open eaves is a different proposition. And a 1970s bungalow can still grade moderate if the soffit boards have pulled away.

Timing and the survey season

The inspection can happen at any time of year. Emergence and re-entry surveys cannot. The active season for these runs from May to September, with May to August treated as the optimal window because bats are most active and maternity roosts are occupied.

That asymmetry is the practical planning point. Commission the preliminary roost assessment in winter or early spring. If it comes back negligible, you have lost nothing. If it comes back moderate, you are in the queue for May rather than discovering the problem in June and waiting for the following year.

Councils will not usually determine an application where a likely roost has not been surveyed, because they have a duty to consider the effect on a European protected species before granting permission. Some will not validate the application at all. Our page on the Preliminary Ecological Appraisal covers the wider habitat survey that often runs alongside.

What the report has to contain

For the council to rely on it, the report needs to say who carried out the inspection and on what date, what their licence and professional membership is, what was inspected and what could not be reached, what evidence was found, what category the building falls into, and what further survey is recommended.

Where further survey has been done, the report sets out the dates, the weather conditions, the equipment, the number of surveyors and their positions, and the results by species and by access point.

Where mitigation is needed, it sets out the roost type, the proposed replacement provision, the timing of works, and whether a European protected species mitigation licence from Natural England will be required before work starts. A Protected Species Survey is a report type where a licensed ecologist is legally required, and an AI-assisted draft is a starting point for that professional rather than a substitute for the survey or the licence.

How the category changes the application

A negligible finding is recorded in the report and the application proceeds with the report attached. Nothing else follows.

A low, moderate or high finding changes the documents the council expects. The ecologist's recommendation sets out the survey effort, and the case officer will normally consult the county ecologist or an in-house adviser before determining the application. Where a roost is confirmed, the council has to consider the three tests in the 2017 Regulations before granting permission, covering the purpose of the works, the absence of a satisfactory alternative and the effect on the favourable conservation status of the species.

That is why an application submitted with a moderate category and no follow-up survey tends to stall rather than be refused. The officer cannot lawfully complete the assessment without the information.

Cost and programme for a household scheme

Ecologists price by site and by travel, so ask for a fixed quote once they have seen the address and the drawings. A single dwelling assessment is at the modest end of ecological work. Emergence surveys cost more because they need two or three surveyors on site from before sunset, repeated across separate visits with a minimum gap between them.

Build the sequence into the programme rather than the budget alone. Assessment in February, surveys in May and June if needed, report in July, application in July, decision by September. Compressing that is rarely possible, and starting roof works without the answer risks an offence under the 2017 Regulations that carries criminal liability.

If bats are found, the scheme usually still goes ahead. Timing restrictions, a bat access point in the new ridge, and a licence with a method statement are the common outcome. The bat survey page sets out what that work covers.

You can enter your postcode on PlanScope to see which reports a roof or loft project at your address is likely to need before you commission anything.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional 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.