Wiltshire Council’s new offices on a sensitive historic site in Salisbury are a marriage of a new, low energy, flexible building and the restoration of a Grade II* listed mansion.
Stanton Williams were commissioned following a RIBA competition in 2004 to develop proposals for the redevelopment of a sensitive historic site at Bourne Hill, Salisbury, as the head offices for the local council. The scheme not only revitalises the Grade II* listed Bourne Hill House, but also adds a substantial new building. Central to the project is an integrated vision that combines contemporary interventions with enhancement of the site’s natural assets and recognition of its significant historic context, which includes attractive gardens, the remains of Salisbury’s city walls, and St Edmund’s Church, now used as an arts centre. Bourne Hill is located at the north-eastern corner of Salisbury’s medieval grid of streets. It includes the remains of the old city ramparts and the site of the thirteenth century St Edmund’s College. Although it sits at the edge of the historic city, contemporary Salisbury has, of course, grown well beyond that. The new Council building is a marriage of the new building and the restored Bourne Hill House and faces both south towards the city centre and north to the neighbourhoods beyond.
The new building is set slightly apart from the historic house with a narrow glazed section delineating the boundary between the two. It comprises two interlocking cubic volumes, each reading as an L-shaped unit. One is of two storeys, the same height as the house itself, whilst the other is taller. The impression, therefore, is of a building stepping back as it meets its historic neighbour. Within, 2600m2 of flexible, open plan offices enjoy good views of the surrounding gardens. Movement within the building is focussed along a central route that links the mansion entrance to the new garden entrance via two triple-height glazed spaces. Adjoining this route, a central vertical circulation core in the new building gives access to all levels – including the 17 different levels of the old building.
Externally, the new building is given presence and scale through the use of a full-height colonnade set in front of its glazed elevations. The colour and texture of its Roach-bed Portland stone adds visual interest whilst also responding to the materials of St Edmund’s Church and the historic city. Its use thus creates a striking visual link between old and new. The colonnade creates an attractive place in which to walk at the boundary between architecture and nature, with its columns framing glimpses of trees in the garden beyond that are reflected in the glazed behind. The result is a rich interplay of transparency, reflection, light and shadow. There is a strong relationship between the architecture and the external landscape. Inside and outside spaces interlock. The colonnade is conceived as a “screen” and part of this landscape space. The reflective surfaces of the emphatically vertical glass facade replicate the surrounding trees and views, and bind the building to its context.
The mansion, Bourne Hill House, has been fully restored. Dating principally from the eighteenth century, Bourne Hill House, has been used by Salisbury District Council as offices. A substantial brick building arranged around three sides of a courtyard, it had been subjected to a series of detrimental external additions dating from the nineteenth century and later. These accretions have been swept away, reinforcing the architectural integrity of the house, and its dominant presence within the surrounding gardens. Internally, partitions have been removed to reveal the building’s original grandeur. On a sensitive site and within an historic city, the final design was arrived at following an extensive process of consultation with the local community and with expert bodies including English Heritage and the amenity societies
Improving accessibility has been central to the design vision. Previously, disabled visitors to the historic house could access the main entrance but no further. 17 different level changes have been rationalised as part of a coherent access strategy. The design of the new adjoining building allows simplified circulation throughout the historic house, opening up previously private areas for the community, and improving accessibility to all areas. For example, a previously inaccessible locked room was being used as a computer server room. This is now restored to its former grandeur, creating a fully accessible room for public ceremonies. A lift in the new building and two platform lifts in the historic house, together with glazed links between new and old spaces, provide a step free route through and around the buildings. Ground floor interior spaces are linked by a fully accessible route between the historic portico entrance and the new building entrance, which is level and flush with the ground and accessible from the paved colonnade. Accessible toilets are now available on all levels, as part of the main cloakroom facilities. Hearing loops have been installed to new and old meeting rooms and the newly opened up public ceremony room.
The whole development uses a sustainable and minimal energy design strategy in the building’s form and engineering systems. The project has achieved a BREEAM rating of ‘Excellent’ and EPC rating of B. Use of natural light and ventilation has been maximised, using simple, proven, cost effective measures, executed well and without employing costly, on-site renewable energy systems. The new structure is exposed heavyweight in-situ concrete which eliminates the need for mechanical cooling to the office spaces. The concrete uses 55% GGBS (Ground Granulated Blast furnace Slag) cement replacement mix. GGBS is a by-product recycled from blast furnaces which greatly improves sustainability of the material. Structural Engineers AKT and Stanton Williams developed the concrete specification and worked with the contractor to achieve the highest quality finish possible, through sample panels and experimentation with aggregate. It is believed that the use of GGBS cement replacement reduced the amount of embodied carbon in the structure by about 20%.
High performance glass minimises heat loss and solar gain, but allows a high percentage of daylight through to minimise the need for artificial lighting. Ventilation openings, which can be operated manually or by automatic control of insulated panels forming part of the façade, are secure and plentiful, to allow night-time cooling and good ventilation during the day. Elegant fins on both facades of the building, clad in Portland Roach stone to reflect materials used in the refurbished listed building, provide solar shading, and on the western façade form a colonnade, linking the building to the historic landscape. Heating is gas based (condensing, compensated and variable flow), provided by trench heaters adjacent to the façade of the building and flush with the floor finish. The trench heating is zoned so that it can be individually controlled in small sections, ensuring that only occupied areas are heated as required.
Sustainable measures include rainwater recycling and water harvesting, passive cooling, natural ventilation and both green and brown roofs. The green and brown roofs insulate the building and act as a sponge to slow down water run-off and help avoid problems with drainage. The green roof includes sedum planting and the lower maintenance brown roof uses reclaimed waste rubble and timber scattered with wildflower seeds to reflect the local environment and encourage increased biodiversity in the area. The design team worked closely with English Heritage to develop a series of delicate repairs to the historic house, avoiding any wholesale re-building of the structure, and using traditional materials such as hair lime plaster, welsh slate, lead guttering, timber laths and local stone. Full repairs were carried out to the roof, masonry, plasterwork, external render and garden walls. Sculpted timber seating in the gardens by artist Karen Hanson reflects the natural process of aging and are made from reclaimed timber recycled from the site.