Introduction

Project description
The owners/residents of a tythe barn proposed to convert its west/mid-sections into additional residential. Day roosts for Natterer’s, brown long-eared and common pipistrelle were present. Mitigation included integrating a bat loft into the existing barn space under EPS licence. Post-development monitoring confirmed continued bat presence afterwards.
Ecologist’s name and contact details
Arcadis (Paola Reason - now RSK Biocensus)
Planning authority
Stroud District Council
Brief site description
‘The Barn’ is located in a rural setting surrounded by a garden with scattered trees and shrubs. The surrounding area is largely arable land with small parcels of woodland. There is a patchy linear network of hedgerows. Two separate buildings are situated south of the barn on the adjacent landholding.

Pre-works roost structure

Type of structure
Building
Use
Agricultural Building
Condition
Not In Use
Approx. age
15th Century
Main construction material of walls
Timber
Roof design
Pitched Roof
Roof material
Corrugated Tin
Internal roof structure
Timber Frame
Lighting present on site and its proximity to the roost
Limited

Pre-works roost description

Species
Brown long-eared bat
Number of bats max count
8
Type of roost
Day Roost
Evidence of bats
Bats Recorded Emerging/Re-entering
Roost location
Other
Aspect of roost
Other
Height of roost entrance (m)
8m
Roost material(s)
  • breezeblockConcrete
Nearest commuting feature
Hedge
Distance to nearest commuting feature (m)
40m
Nearest artificial light source to roost commuting route
None recorded

Proposed works

Description of works
The mitigation strategy was designed to safeguard bats and minimise disturbance via: sensitive timing of work to commence in the late autumn; initial toolbox talk to contractors; creating a dedicated bat loft with new access points; and minimise lighting.
Type of impact upon the roost
Long-Term Roost Modification and Roost Loss

Proposed mitigations

Type of mitigation
Compensation
Specific technical detail of measure
Part of the existing barn roof beneath the ridge beam was modified into a dedicated bat loft. The dimensions were 2.2m floor-to-apex; 4.2m long and 4m wide at the floor level. These loft dimensions satisfied the recommended guidelines for the minimum acceptable void height for brown long-eared bats (2m with an apex length or width of 4m). This section of roof was already lined with traditional bituminised under-felt, which continued to provide a surface on which bats could hang. The loft remained unlit and un-heated, but insulated to ensure comparable roosting conditions to the previous situation. 4 x internal bat boxes were provided to mimic artificial mortise joints. Roughened 150mm timber boards / planks supported on vertical battens fixed to the breezeblock wall were also provided as additional crevices. Timber-clad areas on the stud wall created artificial crevice gaps for bats. Bat access was provided via a dormer bat access feature on the south-facing roof pitch - 300mm wide x 200mm high. The dormer was shielded (but not baffled) on the interior via a roughened board fixed adjacent to the ridge. This maximised the unobstructed roof-space but impeded airflow - creating areas that were protected from draughts. This type of shield also discouraged the use of the bat loft by nesting birds. This was designed to provide fly-in access to the loft, mirroring the use of existing access points. It also allowed access by lesser horseshoe bats (though lesser horseshoes did not use the barn extensively). 2 x purpose-built raised ridge tiles were also provided on the S elev. These had small gaps beneath (70mm x 18mm) through which crevice-dwelling species could gain access to the void. The small size was to reduce draughts and avoid bird access. Gaps were cut in the existing roof lining to ensure bats could access the roof void.
Roost location
In Roof Void
Aspect of roost
S
Height of roost entrance (m)
7 - 9m
Roost material(s)
  • Bitumen Felt
  • Timber
Nearest commuting feature
Hedge
Distance to nearest commuting feature (m)
40m
Internal temperature and humidity of roost
27 degrees
External temperature and humidity of roost
22.4 degrees
Nearest artificial light source to roost
None recorded
Nearest artificial light source to roost commuting route
None recorded

Monitoring data

Length of monitoring proposed
2 Years
Frequency of monitoring
1-3 per year (depending on monitoring outcome)
Type of monitoring
Roost Inspection
Date and time
3rd April 2014 02:00
Evidence recorded
75 x small (Pip / small Myo) bat droppings recorded on loft floor. This confirmed continued bat presence.
Interventions made
None
Type of monitoring
Roost Inspection
Date and time
11th July 2018 02:00
Evidence recorded
2 x brown long-eared bats (confirmed via DNA analysis) emerged from the fly-in access point on the southern pitch of the central roof. A single soprano pipistrelle also emerged from behind the timber cladding and a single Natterer's bat observed inside the bat loft.
Internal temperature and humidity recorded
27 degrees
External temperature and humidity recorded
22.4 degrees
Interventions made
None

Final details

Lessons learned
To be completed