Project description
A challenging mitigation site where a derelict Georgian mansion perched on top of the remains of a medieval castle was to be turned back into a grand property open to visitors; for displays/classes and holiday accommodation. Keeping a direct internal link was considered important so a flight tunnel was created.
Ecologist’s name and contact details
Richard Crompton, Ecology on Demand
Client’s name
Cadwgan Building Preservation Trust
Site postcode
SA43 1JA
Planning authority
Ceredigion County Council
Brief site description
Cardigan Castle has a long association with bats - there is a credible description of greater horseshoe bats using one of the stables buildings in the 1970's. Considerable studies by Tom McOwat in the 90's and 00's told us that a small colony of GHS bats used the Castle regularly as well as pipistrelle and brown long eared bats. As the main house became increasingly dilapidated and the Cadwgan Building Preservation Trust set out to raise the £11m needed to restore the building and surrounding Regency Gardens in a ten year restoration project that finished in 2015. The restoration won RICS Welsh Architecture Project of the Year Award and the Royal Society of Architects in Wales Conservation Award in 2016.

Pre-works roost structure

Type of structure
Approx. age
1176 Medieval castle cellars, with Georgian House and Regency Gardens
Main construction material of walls
Roof design
Roof material
Internal roof structure
Timber Frame
Lighting present on site and its proximity to the roost
Limited external security lighting has been added - using low level and bollard lights - most triggered by PIR sensors. However, some large public events (concerts etc) are held where additional lighting is utilised.
Photos or annotated figures of roost structure

Pre-works roost description

Greater horseshoe bat
Number of bats max count
Type of roost
Mating Site
Evidence of bats
Bats Seen in Roost
Roost location
Aspect of roost
Height of roost entrance (m)
One at ground level, x2 at roof top (c.8m)
Roost material(s)
  • Slate Tiles
  • Timber
Nearest commuting feature
Distance to nearest commuting feature (m)
Internal temperature and humidity of roost
6.5-7.7C, 95-100%RH
Nearest artificial light source to roost
Nearest artificial light source to roost commuting route
Photos or annotated figures of roost

Proposed works

Description of works
The "Castle" (the Georgian section of Castle Green House) had become derelict and was collapsing. A scaffolding roof was in place for many years as the project raised funds. Surveys by Tom McOwat (and with input from Dr Bob Stebbings and Dr Maggie Andrews) suggested that the site may be used by mating greater horseshoes as well as various other species. The greaters' were usually present in the cellars, attics, and a 1st floor cupboard throughout most of the year. Site Ecology Work was managed by Wildwood Ecology.
Type of impact upon the roost
Long-Term Roost Modification and Roost Loss
Relevant annotated figures

Proposed mitigations

Type of mitigation
Specific technical detail of measure
The key mitigation feature for this example is an underfloor link tunnel which was drilled several metres through the medieval stone walls into the cellar and linking to a c4m under floor tunnel (400x300mm, although slightly lower under each floor joist due to levels). This then joins a vertical ‘bat riser shaft’ (700x600mm) which travels vertically up past ground, first and upper first floors and into the attic. This shaft was made possible because it as adjacent to the newly installed lift.
In the attic horseshoe bats have a further two louvre style accesses in east and west attics to provide alternate access to the consolidated and light baffled access point at ground level in the cellar. A contained barn owl box with a dedicated external access and no access into the attic was built as a enhancement measure (barn owl had roosted regularly in the derelict building but no evidence of nesting was ever been confirmed). Crevice gaps were made in the eaves to allow smaller bats in too.
In the wider site a further attic was made available to greater horseshoes although this has not been used to date and some bat boxes were installed within the grounds.
The flight link has now been confirmed to be used by greater horseshoe bats which are normally resident year round again. Pipistrelle droppings have been found in the attic along with a small number of probable BLE droppings too.
Relevant annotated figures
Roost location
Aspect of roost
Not Applicable
Height of roost entrance (m)
One at ground level into cellar, x2 at roof top (c.8m), plus small access gaps for crevice dwelling species across all aspects and under the eaves.
Roost material(s)
  • Brickwork
  • Stone
  • Other
Nearest commuting feature
Distance to nearest commuting feature (m)
Internal temperature and humidity of roost
6.5-7.7C, 95-100%RH
Nearest artificial light source to roost
Nearest artificial light source to roost commuting route

Monitoring data

Length of monitoring proposed
Frequency of monitoring
annual (plus more frequent ad-hoc)
Type of monitoring
Roost Inspection
Date and time
10th March 2016 12:00
Evidence recorded
2 GHS bats seen in cellar, 1 in attic. Up to 5 have been seen on other occasions
Interventions made
Some additional 'pigeon-proofing' of attic louvre access required.

Final details

Lessons learned
Considerable previous bat data was invaluable for this project and the architect Izaak Hudson was superb and really seemed to relish the challenges. Better liaison between the principle contractors and the ecologist would have helped avoid some mishaps during the restoration works. Due to the long term monitoring requirement of this project (10 years and beyond!) it was suggested that the Castle team identify a bat champion to be the go-to person. Mark Dellar the Estates Manager stepped forward and has really helped to make the bats a feature of the castle; following some training he was made an agent under RC’s personal bat licence for the site, and now undertakes monitoring as well as any unavoidable maintenance in the bat areas, and also leads carefully controlled public group visits into the historically important medieval cellar during the warmer months of the year (no access in winter). An infrared CCTV camera has also been installed so visitors can zoom in on any bats using the cellar from day to day. These extra steps have shifted the bats as an inconvenience during the restoration project to an asset regularly enjoyed by visitors.