Sharpham House Courtyard Lesser Horseshoe Roost Preservation

Introduction

Project description

Preservation of a Lesser horseshoe maternity and hibernation site above a Grade II listed courtyard of buildings on the Sharpham Estate

Ecologist’s name and contact details

Jason Gillingham jason@jgecologicalsurveys.co.uk

Client’s name

The Sharpham Trust Charitable Organisation

Planning authority

South Hams

Brief site description

The Coachyard which is synonymous with Sharpham Courtyard for this document and the associated EPSL, consists of the four buildings set around a central courtyard. The roost was located above the only inhabited structure on the east of the courtyard. The site was surrounded by the 550 acre estate adjoining 3 miles of the River Dart. To the west was the walled garden with deciduous woodland beyond, to the north woodland and grassland with the Dart beyond, to the east was Sharpham House with the more formal garden areas, the latter extending around the south of the courtyard as well. The interior roof spaces were complex due to works through history adding ceilings and false ceilings creating a network of interlinked roof spaces. The Sharpham Trust owns the site, it is a charity that exists to connect people with nature and to foster mindfulness, health and wellbeing by delivering residential and non-residential courses, programmes and events. The residential courses attract over 1,500 people per year and for many the courses are part of their continued mental health recovery. The conversion of the courtyard was to provide additional accommodation units to enable more people to attend and benefit from the courses on offer.

Pre-works roost structure

Type of structure

Building

Use

Other

Condition

Not In Use

Approx. age

200 to 300 years old

Main construction material of walls

Stone

Roof design

Pitched Roof

Roof material

Slate

Internal roof structure

Timber Frame

Lighting present on site and its proximity to the roost

Floodlights were located within the courtyard and on the approaches to the site entrance prior to works commencing

Photos or annotated figures of roost structure

Pre-works roost description

Species

Lesser horseshoe bat

Number of bats max count

143

Type of roost

Maternity Roost

Evidence of bats

Bats Seen in Roost

Roost location

In Roof Void

Aspect of roost

Various

Height of roost entrance (m)

3

Roost material(s)

• Bitumen Felt
• Slate Tiles

Nearest commuting feature

Treeline

Distance to nearest commuting feature (m)

4m

Internal temperature and humidity of roost

Variable as both a maternity and hibernation roost refer to attached data

External temperature and humidity of roost

16 to 18 C as multiple surveys carried out

Nearest artificial light source to roost

flood lights within courtyard

Nearest artificial light source to roost commuting route

flood lights

Photos or annotated figures of roost

Proposed works

Description of works

The Coachyard which is synonymous with Sharpham Courtyard for this document and the associated EPSL, was a key asset of the estate but was being underutilised and in deteriorating condition. Residential courses at the Trust were previously limited by availability of accommodation. A plan was put forward to convert the courtyard into 18 separate rooms with a shared kitchen, living area and dining room. Ecology was considered from the pre-application stage onwards with the bat roost being highlighted as a critical constraint. This enabled the design criteria to be set prior to any plans being compiled. The architect, Mark Ledgard of Savills, then took the constraints posed by the resident bat colony and the site’s Grade II listed status and came up with the solution of inserting the accommodation units into the existing listed structure thus minimising any impacts on the bat roosting areas and creating a void beneath the existing ceilings to enable the services (water, electric, fire alarm cables etc) to be run to each room once again with minimalimpacts on the bat roosting areas

Type of impact upon the roost

Disturbance

Relevant annotated figures

Proposed mitigations

Type of mitigation

Avoidance

Specific technical detail of measure

Retention of all existing ceilings and false ceilings via insertion of living accommodation beneath the existing features thus enabling the bats to remain mostly undisturbed by the works. Please refer to previous section for figures illustrating how this has been achieved.

Roost location

In Roof Void

Aspect of roost

Various

Roost material(s)

Nearest commuting feature

Treeline

Type of mitigation

Avoidance

Specific technical detail of measure

Lighting, the floodlights were removed and replaced with low level down lighters. All lights were set on motion activation, with a timer to limit duration of lighting events. Lights were set at a low height to show doors to accommodation and to light pathways only. Refer to the lighting plan attached.

Roost location

In Roof Void

Aspect of roost

Various

Roost material(s)

Nearest commuting feature

Treeline

Monitoring data

Length of monitoring proposed

The site has been monitored for hibernation since 2009 and for summer use since 2018

Frequency of monitoring

twice each winter (Jan to Feb inclusive) and twice per summer July to August inclusive

Type of monitoring

Roost Inspection

Date and time

13th February 2023 13:00

Evidence recorded

54 Lesser horseshoe bats

Internal temperature and humidity recorded

16.3 C Rh75%

External temperature and humidity recorded

9.6 C

Interventions made

Commitment to place temperature and humidity monitors in the roof space for winter 2023/24

Type of monitoring

Dusk and Dawn Survey

Date and time

24th July 2022 01:00

Evidence recorded

80 Lesser horseshoe emerging

External temperature and humidity recorded

18 C 54% rh

Interventions made

None

Type of monitoring

Dusk and Dawn Survey

Date and time

27th August 2022 23:50

Evidence recorded

91 emergent Lesser horseshoe bats

External temperature and humidity recorded

16 C 60% rh

Interventions made

none

Type of monitoring

Roost Inspection

Final details

Lessons learned

The principle lesson learned was that when dealing with a nationally significant hibernation and maternity roost when bats are always present creating a design that inserted the accommodation units into the existing structure and created a void between the new accommodation and the pre-existing ceiling enabled all works including service installation (electrical, plumbing, fire alarms etc) to be carried out with no requirement to access the bat roosting areas. This greatly reduced the during works disturbance impacts to a low level for this complex roost site.

The summer emergence monitoring figures were very close to the pre-works figures, and these coupled with the images from the roost camera showing females with young confirmed that the design solution, licensing strategy and roost retention had been a success. Therefore the lesson learned was that if roosting areas and their characteristics can be retained and a buffer built between these areas and the new living accommodation then the likelihood of a successful outcome is much higher than if the entire building and the roof structure was to be modified.

With regard to the decrease in hibernation figures to a level last seen in 2009, 2013 and 2014 an understanding is needed of what the mechanisms are that have caused this. It is known that winter 2022/23 has been one of the warmest on record thus far and this may have caused an elevation in temperature within the roof spaces (there is no insulation between the slates and the roosting locations and therefore when sunlight hits the slates warming will occur). It is also possible that increased human activity and associated heating within the newly created living accommodation may have caused an increase in temperature within the roof spaces , however the level of insulation and the space between the converted areas and the retained roosts was designed to prevent this particular scenario from occurring. Despite the insulation it is apparent from the monitoring data that the difference between the measured outside temperature and the measured loft temperature shows signs of change since the works were completed. The previous monitoring gave, on average, a minor difference of between 1 and 2°C between external conditions and lowest internal roost temperature, whereas the two most recent visits during 2023 have given 3.9 and 6.7°C warmer within the roof voids than outside. This has happened before (2011, and 2014) with no detriment to continued use of the site but is worthy of further investigation. With no long term monitoring of roost temperature profiles through all the winter period for the years when high numbers of bats were present and those years when fewer used the roost it is not possible to ascertain whether this has been one of the causes for lower levels of use. Going forward it is proposed to put temperature monitors within the roof spaces to assess any impacts when courses are running and the heating is on versus when no courses are running and the heating is lower. Any measurements taken will need to be assessed against the outside temperatures during the corresponding period so that an appropriate correction factor can be applied, but it is hoped by doing this any impacts from the conversion works measured in terms of temperature changes within the roof space can be assessed. If there is found to be a link between the heating during courses and a raised temperature in the roof spaces corrective actions will be adopted including lowering the heating level in rooms directly below the key hibernation sites, and assessment of whether additional insulation material should be added in the void between the accommodation and the pre-existing false ceilings to mitigate any impacts.

There is also the possibility that any minor disturbance impacts during works which caused bats to adopt other hibernation roost sites (in this area of south Devon many opportunities appear to exist) during the conversion period may have caused the decline. If bats moved to alternative roost sites they may now have developed a roost loyalty to that location.