Bats have declined in significant numbers in recent years. With the loss of many trees suitable for bat roosts, certain species have adapted to roosting in buildings, where they can be affected by any structural or renovation work or remedial timber treatment.

Bats and the law

All 15 species of British bats and their roosts are protected under the Wildlife and Countryside Act 1981. Under Section 9, it is illegal for anyone without a licence to intentionally disturb, injure or kill a wild bat; to possess or exchange a bat, or to intentionally damage or obstruct access to any place that a bat uses for shelter or protection. (Full details in Sections 9-11, 16-27 and 69 of the Wildlife and Countryside Act 1981).

This law need not make life difficult for builders or property owners who wish to carry out essential work and find bats present. Where bats or their roosts (even if empty) are likely to be affected, the Nature Conservancy Council (NCC), the government’s agency for natural conservation, must be consulted before work begins. The earlier the NCC is consulted, the easier it will be to accommodate bats in any particular situation and to minimise any possible inconvenience or delay to the work.

To work within the law, the main points to be aware of are:

  1. That any building, in particular the walls, caves and roofs, are potential roost sites.
  2. Anyone working regularly in such areas, e.g. surveyors, architects, plumbers, roofers, builders, timber treatment contractors, insulators, etc., should be aware of what signs to look for and be prepared to report to the NCC on finding them.
  3. If work has already started when bats or their roosts are discovered, the NCC must still be contacted at the first available moment.


Advice will vary according to such factors as the time of year and the species involved. Whether the NCC suggests excluding the bats or temporary postponement of the work will also depend on the attitude of the property owner and the nature of the work at hand.

Certain timber treatment chemicals, such as Lindane (gamma HCH) and pentachlorophenol, are highly toxic to bats, even months after application. The NCC can advise on the full range of commercial products available that use safer alternatives, such as permethrin and Borester-7.

Roost sites

Species vary in behaviour, colony size and roost preference. In general, bats change roosts throughout the year, looking for warm sites in summer and cold sites in winter. They will also change according to weather, food availability and breeding needs.

Colonies are faithful to their traditional sites and will continue to return annually as long as the site is suitable. Usually, roosts found in houses will be maternity roosts of pregnant females and females with young, present between May – August. Immature bats, adult males and nonbreeding females will occupy a variety of roosts, individually or in small groups. Bats undoubtedly hibernate in houses in winter but are rarely found.

Roost recognition

Bats do not make nests and do no structural damage, so the most obvious signs to look for are droppings. They are brown or black, 7-12mm long, and different from rodent droppings in texture, consisting largely of insect remains which crumble to a fine powder when rubbed between finger and thumb. Mice droppings are smooth and sticky when fresh, becoming hard with age. Those of bats do not normally smell strongly, unless the area they occupy is poorly ventilated. Nor do they represent a health hazard.


Typically concentrated around roost entrances and under the sites where bats hang. Pipistrelle bat droppings can be found on the outside of the house on the ground, window ledge or wall below their entrance. Brown longeared bats tend to leave a characteristic scatter under the ridge beams.

The quantity of droppings readily visible in a roof may not necessarily reflect the number of bats using the roost. Pipistrelles usually crawl into crevices behind roofing felt, cavity walls or under ridge tiles and so rarely scatter droppings in accessible areas of the roof. Conversely, large accumulations beneath ridge beams and gable ends, and around chimneys, may reflect use over a considerable number of years.

For further advice

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