Accommodating Bats in Buildings
What do bats look for in a home?
Like us, bats are looking for shelter that is clean (free of disease and parasites), comfortable (protected from the weather) and secure (safe from predators and disturbance). However, bats also have unique requirements and may live in several different roosts throughout the year depending on their seasonal needs.
A number of factors are very important when considering roosts for bats including:
Temperature is very important to bats. Bats are different to us in that they look for warm roosts in the summer and cool roosts in the winter.
Summer: Bats usually only have one young a year. Mother bats gather together and find somewhere warm to rear their young called a maternity roost. Males will form smaller roosts elsewhere that are often cooler than the needs of the females. Generally maternity roosts are usually between 30 and 40°C, however species can have their own unique preferences and studies have shown that even a 1.5°C difference may influence bats to choose one building over another. It is always best to provide a number of different options for bats, so that they can choose the right roost with a temperature based on their needs.
Winter: British bats feed on insects which are scarce in the winter. Bats have adapted to this seasonal scarcity by going into hibernation where they lower their body temperature to the ambient temperature or just above. Hibernation roosts are often a cool space with high humidity. For most species this is generally between 0 and 6°C, however horseshoe bats prefer slightly warnmer conditions of 6 - 10°C.
Aspect and orientation
Summer maternity roosts in the northern hemisphere often have a southerly or westerly aspect for maximum solar heating. Male roosts and hibernation sites typically have a northerly aspect.
Creating roosts in buildings
The advice below describes general principles to consider when providing new roost spaces for bats. It does not provide sufficient information for mitigation when a roost is already present. Work on existing roosts should be covered by a Natural England EPS licence.
Access, size of roost space and structure
• Crevice-dwelling bats can crawl into their roosts via gaps from as small as the width of our thumb. The roost area should contain a crevice of this approximate size gap that the bats can roost in. The height of entry can be from 2 - 7m.
• Roof-void dwelling bats require similar dimensions to access the roost but typically need timber joists or beams on which to roost. The height of entry can be from 2 - 7m.
• Bats needing a flying area require the same access dimension as mentioned above. These areas are typically empty / uncluttered loft spaces to allow flight.
• Horseshoe bats need a larger access so that they can fly (instead of crawl) directly into the roost. As above, the roosting area should not be trussed / cluttered, to allow flight.
Materials and structure
Materials for the roosts should be rough (for grip), non-toxic or corrosive, with no risk of entanglement. The materials should also have suitable thermal properties that reduce 24 hour fluctuations but allow maximum thermal gain for summer roosts.
To view or upload case studies of bat roost replacement or enhancement visit Roost.