Our cities are dotted with ‘grey field’ infrastructure sites, which are left undeveloped despite being in prime urban locations. So how do we unlock their potential?

A team led by architects Bates Smart has created a new hybrid development – infrastructure/commercial – which will allow for more intensive use of our cities’ infrastructure sites in the future.

“Cities are moving beyond the Age of the Automobile,” said Bates Smart director Philip Vivian. “This has encouraged cities to grow outwards at low densities and created vast amounts of unsightly infrastructure.”

“Cities are now competing with each other to create great urban environments in the city, rather than efficient transport to a suburban ideal.

“As part of this movement, urban regeneration involves repairing the damage of former city visions; including freeways slicing through formerly connected neighbourhoods, inappropriately located infrastructure, and roads designed primarily for cars rather than pedestrians.”

Vivian said design solutions need to place people before machines to improve the urban realm, and must involve creative collaboration between city officials, architects and engineers.

“There are significant opportunities to add life to structures that were previously unusable,” he said. “There is no reason for us not being able to build office buildings over freeways, for example.”

As part of Bates Smart’s Sydney 2030 Vision, the company has proposed under grounding the Darling Harbour freeway network to better connect Darling Harbour to the water and the city. Air rights development enables buildings to be constructed on top of underground freeways, essentially making the economic investment in improving the public realm viable.

A manifestation of this approach can be seen at 180 Thomas Street. The site, in the Sydney city edge precinct of Haymarket, has all the hallmarks of a great development location. It is situated between the historic 19th century semi-industrial Sydney Markets and an emerging tertiary and media precinct. But an existing substation on the site had seen 12 years of aborted attempts by other architects to unlock its potential.

Bates Smart’s solution, for what is now the central Sydney offices of infrastructure company Transgrid, is what Vivian calls, a “synthesis of architecture and engineering.” It turns an active piece of infrastructure into a dynamic new office complimented by public art and ‘hole in the wall’ cafes fronting a new public walkway.

The existing sub-structure incorporates a structural grid and lift core to allow for the construction of a commercial building over top. However, the floor area and structural grid were small by current workplace standards (only 1,200 square metres) and a centrally located lift shaft bisected the floor plate in two.

The challenge was how to increase the size of the floor area, and provide a modern open plan floor plate within the constraints of the existing infrastructure.

The vision was to relocate the central lift core to the perimeter of the building creating an open flexible floor plate.

The architects worked with Enstruct to develop a unique structural solution. Locating steel transfer trusses on the roof of the existing structure allowed the office structure above to have longer spans while creating the opportunity for the building to cantilever beyond the original sub-structure, increasing the floor area.

Using lightweight steel frame construction, the floor-to-floor height has been reduced by incorporating the chilled beam ducts within the structural beam depth. This created the opportunity to accommodate the load of an additional floor without reinforcing the existing structure

Internally, a modern open play layout has been created by relocating the lifts to the exterior of the building to open up the floor plate. The new glazed exterior lifts create a spectacular experience when entering the building.

The exterior is expressed as a set of random stacked boxes. With contrasting shading strategies, this building boldly interprets its diverse context and has created a unique environmental aesthetic. The sub-structure was re-clad in precast concrete panels to create a solid and robust appearance to the base in contrast with the lightness of the glazed volumes above and allowing it to visually support the new structure over.

The base building has achieved a 5 Star Green Star rating through incorporation of passive solar shading strategies and chilled beam cooling. The fit-out has received a 6 Green Star As Built rating, one of only four projects to achieve this rating in NSW.

“This new typology leads the way to a more intensive and humane use of our city’s civic infrastructure sites in the future,” said Vivian.

There is no doubt that issues such as remediation and economic viability mean that brownfields and grey fields are a challenge – the 12 years of failure preceding the current solution at 180 Thomas Street is testament to that. But there are significant advantages associated with the reuse of these sites:

• Energy Conservation: Energy is conserved through the re-use of existing structures and by re-using the “embodied energy” in existing building materials
• Environmental Protection: The environment is protected by cleaning up hazardous sites
• Urban Revitalization: Urban areas are revitalized by reusing vacant industrial sites
• Efficient Utility Use: Development can be promoted near existing electric, sewer, and water utilities
• Economic Development: Economic growth can increase, especially in urban areas
• Sprawl Reduction: Sprawl is reduced by reusing sites instead of developing open areas.