Green Square Library's sunken garden at night time; Green Square Library's sunken garden at night time;

Green Square Library, Sydney

Creating an underground library in an inner city marshland

With population pressures rapidly reshaping our cities, we are seeing unprecedented densification. One of the largest urban regeneration projects in Australia, Green Square, will be home to more than 61,000 people by 2030. Just 3.5km from Sydney’s CBD, the neighbourhood is transforming the city’s oldest industrial area into a vibrant, sustainable and connected community, creating a new style of urban living.

Next to the train station, the new Green Square Library and Plaza are at the heart of the town centre, which was once marshland and below the water table. Arup’s expertise across 17 engineering disciplines was vital in transforming the architects’ underground vision into a reality. Our civil and structural engineering initiatives have ensured this underground library is waterproof and safe. 

Arup has helped create much needed community infrastructure, while also enabling new green space both key priorities for the City of Sydney as it seeks to support rapid growth and enhance liveability. 

The precinct includes a slender glazed entry, a huge underground open plan library with high levels of light from skylights, a sunken garden, a six-storey glass tower with music and reading rooms, and a technology lab with views over the plaza and a public amphitheatre. The plaza is framed by a ring of trees and includes a lawn for reading and pop-up events, a water play zone and a mix of fixed and movable plaza furniture.

Project Summary


11,000 people have moved into Green Square since 2000

61,000the expected population of Green Square by 2030

17disciplines guided the architect through the project lifecycle

The winning design

Our team worked with the architects (Stewart Hollenstein in association with Stewart Architecture) to initially win a global design competition for the new public library, and then throughout the project lifecycle. The sunken library design went against the competition brief – to stay above ground due to the area being a former flood prone marshland – however it created much needed green open space at ground level. 

It is a civil and structural engineering feat to have an underground library in a previously contaminated, reclaimed marsh. ”

Cameron Dymond Australasia Commercial Property Leader

Layers of resilience

Having both swamp-like underground conditions and the permanent water table above excavation level was a significant early challenge. Waterproofing strategies were developed between council, architect, waterproofing and buildability experts, the builder and Arup. We provided clever and complex civil and structural engineering solutions to support the architect with waterproofing to protect the library from the damp earth at the sides, and from the rain above.  

We designed four layers of defence to enable the structure to be sunk safely into the ground, while also minimising seepage of the surrounding water table. Our multi-barrier approach to mitigate water ingress included a tanked basement structure held down with tension piles, an interlocking internal concrete retaining wall, a high level of crack control bonded to the water proof membrane and a spoon drain inside a dry-wall. 

Structurally the site is like trying to build in jelly, things wobble around and have no adhesion or strength. Then add into the mix the water from being under the water table. Having all these challenges combined in one location is unusual, so it’s a terrific accomplishment for all collaborators on the project to have overcome all these challenges successfully. ”

Jane Nixon Jane Nixon Associate, Buildings

Maximising daylight, keeping rain at bay

To bring to life the vision of circular skylights peppered across the roof, our façade, lighting, mechanical and ESD engineers collaboratively designed 40 large skylights which are trafficable and weatherproof. The skylights are safe and strong enough for people in the plaza to walk on, and large enough to provide high levels of daylight into the library. They also limit external heat gain and keep rain at bay. Careful detailing was also achieved in the illumination of the skylights at night, which provides a safer environment and visual interest to the public realm. 


A unique entry way

Arup’s team pushed the boundaries of engineering on the library’s entry pavilion – a slender, delicate glass triangular structure - to ensure it was as clear as possible while effectively dealing with heat and comfort and conserving energy with its mixed mode ventilation strategy. Our façade specialists designed long fins with rectangular hollow sections to form the 16-metre-high entry triangle, which has no visible bracing. By minimising structural sizes and considering deflection and differential movements of the brittle glass façade, we have created a unique welcoming entrance for the library. 


Innovation behind the bookshelves

Taking into consideration the library’s open plan and full-length perimeter joinery, our team conceived an innovative design for the displacement ventilation system by integrating it within the bookshelves. Air is reticulated along the building’s perimeter edges to joinery, where air plenums and diffusers are located at low level (375mm), allowing seating to be incorporated above them. Our engineering design brings numerous benefits including high level internal air quality, low energy usage, greater cooling efficiency, reduction in cooling loads and improved acoustics due to low velocity diffusers and remotely located fans.

By turning an underground space, which is traditionally stuffy and dark, into an energy efficient building with high levels of natural daylight and air quality, we’ve created a space that’s inviting to spend time in and gives the community both a library and an outdoor public space. Both will be very well used in such a densely populated area. ”

Ryan Crabbe Ryan Crabbe Building Services Engineer

With new hard surfaces added to the Green Square plaza area, managing water flow across the site was a key challenge. Our civil specialists used the landscaping, particularly tree pits, as a major part of the on-site detention system to manage water flow off the site into surrounding storm water systems.

Shortly after opening, the library was recognised with the Architectural Review’s prestigious Library Award – recognising transformative and leading-edge library projects across the world completed between 2013-2018.