Commencing a new development can be complicated enough without the additional consideration of what might be lurking in roofspaces and voids within an existing building. Bats are a common lodger of many existing buildings, probably more so than many people appreciate.
Whilst about half of bat species use holes in trees for roosting, the other half use either caves or buildings. As natural roosting sites have become scarce due to development, land use change and changing building practices, so the importance of artificial roost sites has increased. The recent move towards low and zero carbon buildings places great emphasis on building structures that are air-tight. Air-tight buildings will not readily have the crevices normally used by building-reliant species of bats in older buildings. Unless positive, proactive steps are taken, there is concern that future housing stock will hold only limited potential for bat roosts for these particular species. With thoughtful and intelligent design, it is possible to design into the fabric of the building ready-made or bespoke spaces for bats that still maintain the airtightness and thermal performance of the building. This is where an experienced architect and design team can help, providing timely advice and suitable integration of bat friendly elements within the project.
Conservation of bats is not only about bat roosts, but equally important is the foraging habitat in the area, and this access to food source combined with suitable design of any external lighting plays just as important a role in conserving bat numbers. External lighting must be carefully designed or ideally, eliminated from areas that bats use for foraging or the routes used to commute between roost and the foraging zones.
As bat numbers in the UK have declined significantly in the last century, all bat species and their roosts are now legally protected in the UK. The precise details of the legislation differs slightly across the various countries of the British Isles but in summary it is an offence to deliberately or recklessly kill, injure, capture or disturb bats, obstruct access to bat roosts or damage or destroy bat roosts, whether occupied or not.
The presence of bats does not mean that building work, roof repairs, pest control or timber treatment cannot take place. However, if any work is going to alter the roost or access space an EPS license (European Protected Species) will be needed. You should consult your local Statutory Nature Conservation Organisation (SNCO) via the Bat Conservation Trust Helpline, before work starts and follow their advice on how to proceed.
A good example of a recent project Grainge Architects have undertaken, involving demolition and new build works, all affected by the known presence of bats is Treliske Medical Residences in Cornwall. The scheme involved significant demolition of the existing outdated building stock and replacement with more modern accommodation. A bat survey identified the existing buildings on site as bat roosts, and the demolition carried out strictly in accordance with and under the watchful eyes of the SNCO and local authority. The existing slate roofs were striped carefully by hand, under supervision of a suitably qualified 'bat expert' prior to the main demolition works. Bat boxes were installed around the site in the existing trees and hedgerows whilst new bat boxes were installed in the new buildings. External landscaping was maintained and reinforced, whilst external lighting was designed to minimise light spill onto the boundary hedgerows that formed the important bat foraging routes.
Whilst this blog isn't intended to provide specialist detailed advice to cover every situation, Hopefully the message one can take from this is that when considering building works, the advice and input of a qualified architect is invaluable and that if it is suspected that bats are present in an existing building with the potential for redevelopment, there is usually a way forward providing advice is sought early enough on in the process.