Bats are a protected species and it’s illegal to destroy, damage, disturb or block access to their breeding and roosting sites. However, the presence of bats doesn’t mean you can’t progress your house project. Hire an ecologist, with the appropriate Natural England licence, to do a bat survey. The outcome will tell you what you need to do to preserve their habitat and stay on the right side of the law. It’s a good idea to start this process as soon as you can to reduce delays to planning approval.

When you might need a bat survey

Bats tend to roost in old buildings and not always ones that are derelict. Planners will request a bat survey if you’re planning on converting a rundown agricultural building, renovating or extending an old property, habitable or not – even if you intend to replace it. Older houses near woodlands, those that need major roof work, repointing because of gaps between bricks, will also be of concern, as will those with weatherboarding and big, empty roof voids. A survey may also be necessary if you’re cutting down trees or demolishing a shed or garage.

What’s involved?

You must have an initial assessment before you do a bat survey. This involves an expert walking around the site, checking the roof and looking into crevices. The expert will be searching for droppings to scope out the possibility of bats. If none are present, then you’ll have this confirmed in paperwork to submit to planning. This costs from £300.

Otherwise, the next step is to commission a bat survey to determine how the bats will be affected by the development. This could be a lengthy process (costing upwards from £1000) and involves an ecologist(s) coming to site at dusk and at dawn, possibly on more than one occasion. The survey will conclude where the bats are located, how they’re using the site, the numbers, species and what must be done to protect them.

Find a licenced expert to carry out bat surveys through the Chartered Institute of Ecology and Environment Management directory (cieem.net/i-need) and Environmental Data Services Directory (www.endsdirectory.com).

When the survey must be done

For some people, a major sticking point to needing bat surveys is that it can only be carried out between May and September, which could delay planning approval. Between dusk and dawn in these warmer months are when bats are most active. They will be feeding on insects that are more prevalent at this time of year. The rest of the time they’re in hibernation and can’t be disturbed.

How to protect bats

Basically, you’ll need to create a new habitat. The mitigation measures to take will depend on the type of species and how the bats are using your site. This can be as a hibernation roost, summer roost or maternity roost. Note that larger species need a void for warm-up flights post hibernation before heading outside. Part of the loft might need to be sectioned off and speciality ‘bat access tiles’ fitted. You will need a raised profile to allow them to come in. Alternatively, you may be able to build a separate bat house outside.

Smaller species will make use of bat boxes fixed to the property, a wall or surrounding trees. It’s worth noting that excessive outdoor lighting and certain chemicals used to treat wood are also considered harmful to bats. Densely-woven breathable roof membranes are also harmful – your ecologist can advise.

Your obligations will be detailed in the ecologist’s report, discussed with planning and become a condition of planning approval. You may not be able to start work on site or implement these changes. This is during the hibernation months, which tends to be November to April.