Introduction
- Project description
- Three redundant barns were converted to three dwellings. Since they originally hosted a breeding Natterer's roost, a percentage of the original mortice joints were retained by means of recessed entrances with minimal glazing.
- Ecologist’s name and contact details
- Patty Briggs
- Planning authority
- North Herts District Council
- Brief site description
- Redundant timber framed barns in farmyard surrounded by arable land with some hedge line trees.
Pre-works roost structure
- Type of structure
- Building
- Use
- Agricultural Building
- Condition
- Derelict
- Approx. age
- 17th Century
- Main construction material of walls
- Timber
- Roof design
- Pitched Roof
- Roof material
- Asbestos-Type
- Internal roof structure
- Timber Frame
Pre-works roost description
- Species
- Natterer’s bat
- Number of bats max count
- 45
- Type of roost
- Maternity Roost
- Evidence of bats
- Bats Recorded Emerging/Re-entering
- Roost location
- Roof Timbers
- Aspect of roost
- S
- Height of roost entrance (m)
- Tie-beam level
- Roost material(s)
-
- Nearest commuting feature
- Hedge
- Distance to nearest commuting feature (m)
- Not reported
Proposed works
- Description of works
- The aim was to retain the breeding Natterer's roost after conversion by retaining a percentage of the original mortice joints. This was accomplished by means of recessed entrances with minimal glazing. Original access was retained. Building work was also staggered so that bats always had access to at least one of the barns.
- Type of impact upon the roost
- Long-Term Roost Modification and Roost Loss
Proposed mitigations
- Type of mitigation
- Mitigation
- Specific technical detail of measure
- A percentage of the original mortice joints were retained within the converted barns. This was accomplished by means of recessed entrances with minimal glazing. The original access points were retained.
- Roost location
- Under Fascia Boards
- Aspect of roost
- S
- Height of roost entrance (m)
- At tie beam level
- Roost material(s)
-
- Timber Roof Frame
- Nearest commuting feature
- Hedge
- Distance to nearest commuting feature (m)
- Not reported
Actual mitigations implemented
- Type of mitigation
- Mitigation
- Specific technical detail of measure
- A percentage of the original mortice joints were retained within the converted barns. This was accomplished by means of recessed entrances with minimal glazing. The original access points were retained.
- Roost location
- Other
- Aspect of roost
- S
- Height of roost entrance (m)
- At tie beam level
- Roost material(s)
-
- Timber Roof Frame
- Nearest commuting feature
- Hedge
- Distance to nearest commuting feature (m)
- Not reported
Monitoring data
- Length of monitoring proposed
- Not reported
- Frequency of monitoring
- Not reported
- Type of monitoring
- Dusk and Dawn Survey
- Date and time
- 2nd July 2000
- Evidence recorded
- The bats did not abandon the site during the building works due to the staggering of the work. Bat droppings were seen on the paved floor in one of the recessed areas during the first summer after development. Bats were counted emerging from one of the barns at sunset. Breeding not proven. The colony post development was smaller; only 25 in 2000 compared with 45 in 1994.
Final details
- Lessons learned
- Despite the use of the recessed entrances, the number of available roosting sites was still not enough for the colony of Natterer's bats. Although the bats never abandoned the site, the size of the colony is only half what it used to be. I would not repeat this idea but it was worth trying at a time when no-one knew how to mitigate for Natterer's. Nowadays, I would prefer to leave one of the barns most favoured by the bats undeveloped and with strict controls on lighting and use.
1. One problem is new owners installing security lights. This has to be prevented as light pollution does deter Natterer's bats. 2. The architect and the planners changed the plans at the last moment which meant that the original planned three recessed areas was reduced to two plus a small bat loft at a very windy gable end that had no chance of working. 3. The architect claimed that one barn had to be dismantled and rebuilt which meant that they could not retain the original mortice joints used by bats. The planners accepted this argument. This was because of the ‘impossibility of saving any of the old timbers during dismantling’. It was interesting to note that (post development) not only had the barn not been dismantled but that most of the original old beams were still in place. The barn in question was never dismantled during the works; just repaired and stabilised whilst standing.
