Wessex Water, Bath
Provided by Bennetts Associates
Located on a rural site on the edge of Bath, this headquarters building received the highest ever BREEAM rating for a commercial office building. © Mandy Reynolds/Buro Happold.
Bennetts Associates Architects
Address of project: Bath
Construction Cost: £22.5 million
Year of Completion: 2001
Client: Wessex Water
Quantity Surveyor: Davis Langdon & Everest
Structural Engineer: Buro Happold
Services Engineer: Buro Happold
Main Contractor: MACE
The design problem
This project was the fourth in a series of major headquarters by Bennetts Associates that were intended to show, first, how architectural form had a critical role to play in the design of the workplace and, second, how sustainability was consistent with design at the highest level.
The project was acclaimed by the Building Research Establishment as the ‘greenest’ commercial building in the United Kingdom, and its sustainability credentials are well documented through publications and research papers. The building has been the subject of extensive post-occupancy assessment, which has validated the original strategy behind its environmental design.
Local stone and contemporary detailing.
© Peter Cook.
The site is on the outskirts of Bath located on a steeply sloping site in a designated Area of Outstanding Natural Beauty, the building adopts a low profile, barely protruding above the existing stone walls that once surrounded a small isolation hospital. The use of local Bath stone and the careful preservation of existing trees reinforce the impression of a building that is at ease in its surroundings.
Located in an Area of Outstanding Natural Beauty with views to Salisbury Plain in the distance. © Richard Frewer.
The architectural response
Most of the office accommodation is absorbed in three uniform wings that adopt an E shape on plan, each wing facing the sun and looking over the roof of the one below. The wings form a series of south facing courtyards and gardens.
Running down the slope in parallel is a range of communal spaces – an operations room, meeting rooms, a boardroom and catering facilities – that provide a visual foil to the office space and a malleable form that can follow the boundary wall.
In between the offices and the communal areas is a top-lit, linear space that gets progressively narrower as it descends the contours from the main entrance to the woodland at the foot of the site. Glimpses into the offices are complemented by framed views between the communal rooms to the fields beyond.
Embodied energy: Construction of the building broke new ground in terms of embodied energy and off-site prefabrication. Embodied energy was reduced by numerous measures, including the use of recycled materials, pre-cast concrete soffits using 50% less concrete than equivalent in-situ construction, hydro-powered smelters for external cladding and local Bath Stone for external wall cladding and external walls.
Cross Ventilation: The floor plates are limited to 15m in width to optimise the effect of natural ventilation and daylight. The communal spaces that require mechanical ventilation are placed along the west elevation, which acts as a buffer zone to the naturally-ventilated offices to the East. Ventilation of the office areas is via simple opening lights on either side of the floorplate, allowing cross ventilation.
Night ventilation: Pre-cast exposed concrete coffers help to provide about 25w/m2 of cooling during the day. During summer the coffers are pre-cooled during the night through ‘purge ventilation’ via high-level windows controlled by building management system. This then allows the structure to soak up heat during the occupied daytime.
Water conservation: Integrated water management network avoids surface water discharging into existing sewage system. Porous concrete block paving in the car park allows rainwater to percolate into soakaways or large tanks, which feed the irrigation requirements for the grounds. Rainwater is collected to provide 95% of toilet flushing.
Solar controls and shading: The design minimises solar heat gain by orientating the offices along an east-west axis. Solar shading along the south elevation and north lights in the ‘street’ together ensure solar glare and heat gain are minimal.
Biodiversity: Landscape was designed on the discipline of sustainable development and the principles of ecology. The scheme aimed for a 'no net loss, of biodiversity on the site'. The footprint of the building is minimised through the introduction of green roofs and soft paving. The landscaping strategy reinforced the existing flora and fauna, encouraging local wildlife and ensuring the well-being of existing mature trees in a way that enhanced the building's setting.
Awards and assessments:
Civic Trust Award, 2003
RICS Awards ‘Low Energy Award’, 2001
Building Design Awards ‘Building of the Year’, 2001
British Construction Industry Awards ‘Building of the Year’, 2001
FX Awards ‘Best Large Office’, 2001
Aluminium Imagination Awards, 2001
Commendation, Steel Construction Institute Awards 2001
RIBA Award, 2001
Related case studies
Embodied energy, Natural ventilation - cross ventilation, Night ventilation - thermal mass, Water conservation, Solar controls and shading.