Introduction
- Project description
- Fire doors were installed in the roof voids of three National Trust buildings in 2014: Bradenham Manor, Buckinghamshire, Claydon House, Buckinghamshire, and residential cottages at Greys Court, Oxfordshire.
Bat roost access within and exit points from the now-compartmentalised roof voids were maintained by adding vent tiles and shuttered hatches.
- Ecologist’s name and contact details
- Name: Chris Damant. Company: Bernwood ECS Ltd. Address: Hensmans Farmhouse, Nearton End, Swanbourne, MK17 0SL. Email: chris@bernwood.net. Mobile: 07817131683.
- Client’s name
- National Trust. Client: The National Trust. Contact: Jo Hodgkins, Wildlife Advisor – London and South East. Email: joanne.hodgkins@nationaltrust.org.uk.
- Site postcode
- HP14 4HF, MK18 2EY, and RG9 4PG.
- Planning authority
- Buckinghamshire Council.
- Brief site description
- All three buildings are owned by the National Trust and all underwent the same fire safety works through the installation of fire doors within existing roof voids where evidence of bats roosts have been confirmed and bat roost access has to be maintained.
This form will focus on Bradenham Manor, but brief summaries of Claydon House and the cottages at Greys Court will be provided.
Bradenham Manor is located in the centre of Bradenham Estate, just south of the village church. It is a three-storey brick building with a clay-tiled roof dating to the 1670s. The roof has a timber frame, small dormer windows, and a row of brick chimneys along the top. The village itself is situated in a valley and is listed in the Domesday Book of 1086.
Claydon House is a two-storey building, perhaps no more than half of the original building built in the mid-18th century, and is now open to visitors. This structure underwent major redevelopment in the late 18th century, including its stone and brick façades. The section of the roof subject to the installation of fire doors is constructed of traditional timber frame with clay tiled roof.
The residential cottages at Greys Court were likely built in the 16th century on the site of a medieval manor, subsequently fortified before becoming a fashionable Georgian residence. The roof comprises of timber frame with traditional clay tiles.
Pre-works roost structure
- Type of structure
- Building
- Use
- Commercial Unit
- Condition
- In Use
- Approx. age
- 350 years.
- Main construction material of walls
- Brick
- Roof design
- Pitched Roof
- Roof material
- Clay Tiled
- Internal roof structure
- Timber Frame
- Lighting present on site and its proximity to the roost
- No lighting.
- Photos or annotated figures of roost structure
Pre-works roost description
- Species
- Brown long-eared bat
- Number of bats max count
- 4
- Type of roost
- Satellite Roost
- Evidence of bats
- Bats Seen in Roost
- Roost location
- In Roof Void
- Aspect of roost
- Various
- Height of roost entrance (m)
- Various.
- Roost material(s)
-
- Bitumen Felt
- Timber Roof Frame
- Wooden Boarding
- Clay Tiles
- Other
- Nearest commuting feature
- Woodland
- Distance to nearest commuting feature (m)
- 20m.
- Photos or annotated figures of roost
Proposed works
- Description of works
- At Bradenham Manor, the installation of fire doors in the roof void was proposed to protect the building in case of fire, as well as essential repairs to the roof ridgelines. The fire doors would separate the open roof void into three fire safety compartments.
Previous surveys (2011) found the presence of a brown long-eared bat satellite roost, with occasional individuals recorded as present over the winter period. Signs of heavy use led to the conclusion that the roof void had been used as a maternity roost in the past. To allow for continued bat access throughout the roof void, hatches with intumescent shutters fixed open by fusible thermal links were added to the proposed fire doors. These hatches permit the continued bat use of the entire roof void, while the temperature-activated links close the compartments in the event of fire, preserving the function of the fire compartments.
To ensure the bats also have the potential to escape the roof void in the event of fire, pre-existing vent tiles were adapted to form two simple bat access points in each ridgeline within the newly separated fire compartments, in addition to the retained natural bat access points.
The other two National Trust buildings, Claydon House and the cottages at Greys Court, had the same solutions for their proposed roof void fire door installations.
- Type of impact upon the roost
- Disturbance
- Relevant annotated figures
Proposed mitigations
- Type of mitigation
- Mitigation
- Specific technical detail of measure
- An updated roost inspection took place in the lead up to the commencement of works, during which four brown long-eared bats including a juvenile were found, confirming indications of maternity roost usage from 2011. All works were carried out under an agreed Ecological Method Statement which included a pre-start briefing (‘toolbox talk’) for all site workers and ecological supervision by a suitably qualified ecologist. Ridge tile removals and the installation of fire doors were supervised by the Ecologist during periods of mild weather in October and November 2014, a time of year when bats are least sensitive to disturbance should they be encountered.
The fire doors compartmentalised the previously open roof void. To allow continued access throughout the roof void for the brown long-eared bat maternity/satellite roost, hatches measuring 400mm x 300mm with shutters fixed open by heat-activated fusible thermal links were added to the fire doors. The fusible thermal link is designed to break when temperatures exceed 68°C (above the temperatures that roof voids reach in natural conditions), closing the intumescent shutters and sealing the compartment to protect the property from the spread of fire in the roof void.
Pre-existing vent tiles were adapted to form two simple bat access points in each ridgeline within the separate fire compartments, and existing bat access points retained, to ensure the bats still have the possibility to escape after the shutters close.
Claydon House and the cottages at Greys Court both had hatches with intumescent shutters held open by temperature-activated links on the fire doors to protect bat access. Claydon House had the works proceed under ecological supervision in February 2014, after no bat sign was found during pre-works surveys; and the cottages at Greys Court had them proceed in a five-day period subject to ecological supervision in late spring 2014.
- Relevant annotated figures
- Roost location
- In Roof Void
- Aspect of roost
- Various
- Height of roost entrance (m)
- Various.
- Roost material(s)
-
- Bitumen Felt
- Timber Roof Frame
- Wooden Boarding
- Clay Tiles
- Other
- Nearest commuting feature
- Woodland
- Distance to nearest commuting feature (m)
- 20m.
- Photos or annotated figures of roost
Monitoring data
- Length of monitoring proposed
- 2 years post-development.
- Frequency of monitoring
- Proposed annual monitoring, however access permission difficulties post-development only allowed for bat monitoring in 2017 and 2018.
- Type of monitoring
- Roost Inspection
- Date and time
- 13th June 2017 12:00
- Evidence recorded
- 3 brown long-eared bats present at Bradenham Manor including a pregnant female. Fresh bat droppings present, including on fire walls and access points.
- Interventions made
- None.
- Type of monitoring
- Roost Inspection
- Date and time
- 14th September 2018 11:30
- Evidence recorded
- Minimum count of 22 brown long-eared bats in five separate areas across all roof void compartments. Evidence from inspections showing bat droppings on access hatches indicate that they will continue to use Bradenham Manor roof void.
- Interventions made
- None.
Final details
- Lessons learned
- The installation of fire security measures in roof voids to protect people, historic buildings, and their contents from catastrophic fire events has the potential to affect bats roosts, bat access points, and the free movement of bats throughout a roof void by reducing the bats’ abilities to adapt to environmental changes within the void throughout the year.
Traditional methods, including electronic visual and acoustic alarms on fire safety panels, of maintaining fire doors open are prone to risk when doors close, either due to tests or failures in the system, if action is not taken immediately to reopen them.
Working with the National Trust wildlife advisor, their fire safety advisor, and approved contractors led to a simple and efficient low-maintenance mechanical solution that only reacted to real-life fire conditions, i.e. temperatures above 68oC. The devised solution allowed for continued bat access throughout the roof voids. The timing of works and ecological supervision ensured bats and their roosts were protected during construction.
Please note this solution was subject to the fire regulations, insurance, and organisational requirements applicable at the time. Advice must be sought from across a range of disciplines before undertaking any new scheme.
In a seemingly incompatible situation, the addition of a mechanical apparatus that would preserve the use of the roof void for bats and increase the safety precautions taken at these properties highlights the technological solutions that are available.
