Plan for renovations to house

A Bat Mitigation Success Story!

Why do Bats Live in Houses?

Bat habitats have been lost to development over the centuries, leaving the bat’s natural roosting sites, such as trees and caves, in short supply. To combat this, bats have adapted to live in buildings, with many using our homes as their own. However, even these safe havens are vulnerable to renovation, demolition and conversion. All bats in the UK are European protected species, meaning them, their breeding sites, and their roosts are fully protected by law. When planning permission for a house has been applied for, the local planning authority will need to know whether the development will have any effect on a bat roost. If there is any possibility of bats using the property, bat surveys will need to be carried out. These will tell the ecologist what species (if any) are present, allowing the them to decide what mitigation measures are needed. However, this shouldn’t be seen as a negative thing because the ecologist will strive to make sure the development is a success for the homeowner and the bats who live there. This blog post is about a development in the Bridgend area where the ecologist, the homeowner and the construction workers collaborated to create a home that was perfect for both the homeowner, and the bats who depended on it.

The Survey Conducted

Bats in roof void
Bats in roof void

In 2015, Acer Ecology was contacted by a client who needed a bat survey of their property in the Bridgend area. They were planning an extension and needed a bat survey to be done as part of the planning permission. Acer Ecology carried out the preliminary roost inspection and following emergence/re-entry surveys, and found low numbers of brown long-eared bats (Plecotus auritus) roosting within the attic void of the house. Due to this discovery, Acer Ecology ensured that the development works were carried out in a way that had no detrimental effect on this protected species. Development works were undertaken under an EPS license.

The Building Proposal

The client wanted to renovate their house by building a two-storey extension within the footprint of the existing single storey, as well as building a single storey farmhouse extension on the western elevation. The plan included the replacement of the existing roofing tiles, fascias and bargeboards where they tied in with the extension’s roof; however, the rest of the roof was to remain intact.

The Mitigation Proposed and Constructed

Plan for bat void
Plan for bat void

As the clients had no plans to use the attic space, it was decided that it would remain solely for use by the bats. Long-eared species often need a large area to fly around before emerging from a roost, and it meant that the compensation had a greater chance of being successful as the main features of the roost could be maintained i.e. the location, size and access points.

Bat boxes were put in place around the site before any work began on the building to offset any disturbances to roosts during the construction. A chimney stack on the northern elevation of the property needed removing, and this was supervised by a bat specialist to ensure an expert was on hand to relocate any bats during this disturbance.

The mitigation put in place consisted of making the modified attic bat-friendly and familiar to the existing bats by ensuring that the original entrance point into the void and the potential roost were retained. Fascias, soffits and bargeboards with spaces beneath to allow bats to roost underneath were also included. All of the internal exposed woodwork used during the attic construction was required to be of tanalised timber and pre-treated with non-toxic, water based ‘bat-friendly’ formulations.


Post Mitigation of the Attic

Following the mitigation, post-development checks were conducted by a bat specialist to check their success. Further works to the building in question were still to be carried out (building works, electrical works, plastering etc), and the bat specialist was available on-call to deal with any incidents that could affect the bats remaining in the area while this work was taking place.

Annual Monitoring

Subsequently, we have carried out annual monitoring of the bat roost from 2015 – 2017 in the form of an internal inspection, emergence surveys, and an inspection of the access points to monitor the success of the mitigation. During the internal inspection the ecologists found 500 brown long-eared droppings and recorded three long eared bats. During the emergence survey, twelve brown long-eared bats, nine soprano pipistrelle bats (Pipistrellus pygmaeus) and one common pipistrelle bat (Pipistrellus pipistrellus) were recorded emerging from the building. Overall, this project was considered a great success!


This bat mitigation success story shows that collaboration between the owner of the property, the construction workers and the ecologists can yield successful results, benefitting both the wildlife and the public! Due to the dedication of all involved to the preservation and protection of the bats, they were able to continue thriving in their chosen roost, whilst the clients were able to achieve their dreams for their house, proving once again that humans and bats can co-exist harmoniously.

Bat Survey Information   I Need a Bat Survey   Brown Long-Eared Bat Mitigation

Bridgend – Bat Mitigation Success!      St Tewdrics House – Bat Mitigation Project