Bats in the Belfry… But What’s in Your Basement?

When people think about bats in buildings, they usually picture dark church towers, dusty loft spaces, and the classic “bats in the belfry” cliché. While bats certainly do make use of roof voids and bell towers, the reality is far more interesting and far more varied.

Bats are remarkably adaptable animals, using different parts of buildings at different times of year and even shifting their behaviour in response to changing weather conditions. Historic buildings in particular can provide a mosaic of microclimates: warm roof spaces, cool stone cellars, sheltered crevices, and stable underground voids. To bats, these features can be just as valuable as natural caves and tree hollows.

During the summer months, roof spaces often provide the warm conditions needed by maternity colonies, helping females raise their young. South-facing roofs, timber beams, and slate voids can all create ideal roosting opportunities. This association with lofts and church towers has helped cement the public perception that bats are primarily “roof dwellers”.

But that is only part of the story.

In winter, many bat species seek cool, stable, and humid conditions that allow them to conserve energy during hibernation. Basements, cellars, tunnels, ice houses, and other subterranean spaces can provide exactly the right environment. Thick stone walls and underground locations buffer against rapid temperature fluctuations, creating the consistency bats need during colder months.

Interestingly, these spaces can also become important during extreme summer weather.

In a heatwave, surveyors often find no bats within roof voids, due to the exceptionally high temperatures in those areas.  Instead, bats may relocate to features favoured during hibernation or transitional periods such as basements, where temperatures remain cooler and more stable.

Bat roosting behaviour changes with the seasons, weather patterns, and wider environmental pressures. Cooler structures that are primarily used over winter or in transitional periods may become increasingly important refuges as summers become hotter and more prolonged.

For ecologists, this reinforces the importance of understanding the full range of features present within a building or wider estate. Basements, tunnels, service voids, culverts, cellars, and other less obvious spaces can all contribute to the ecological function of a site. However, these features are not always highlighted at the outset of a project, particularly on large or complex heritage sites.

A comprehensive bat assessment relies not only on survey effort, but also on having visibility of all accessible structures and spaces that may provide suitable conditions throughout the year. The more complete the understanding of a building or estate, the more robust the ecological assessment can be.

This is likely to become increasingly important in the face of climate change. As periods of extreme heat become more common, cooler subterranean features may provide valuable thermal refuges for bats and other wildlife within the built environment.

So yes, there may still be bats in the belfry.

But increasingly, it is worth considering what might be roosting beneath your feet as well.