Since the early 1990s, WS2 has housed a popular concrete car park for city visitors and workers. In 2017, GDI Property Group purchased the property, facing a complex challenge: creating a 12-storey building with 9,500 square metres of net lettable space while preserving the underground car park. GDI also aimed to explore sustainable building practices and add value to the Westralia Square Precinct.

Over the past five years, we’ve been instrumental in shaping the new WS2 building in Perth. This innovative project involved designing Perth’s first timber-hybrid office tower through adaptive reuse and engineering innovations. Our multidisciplinary approach included providing structural engineering, mechanical and electrical engineering, acoustics, materials consulting, and facade engineering services. Notable innovations included in-floor dampers and utilising energy capacity from a nearby building’s plant room.

Our adaptive approach to building design in Perth is reshaping future developments. Working with our client GDI, we’re pioneering adaptive design and material reuse. Compared to traditional demolition and concrete construction, our approach has reduced embodied carbon by approximately 70 per cent. GDI is already applying lessons learned from this project to a new building in Perth CBD, setting a new standard for sustainable development in the region.

From the start, it was clear that Arup was more than just an engineering firm. They sought to understand our aspirations, risks, and value add proposition. 

David Ockenden

Head of Development, GDI Property Group

Structural engineering solutions

Through our previous work on the building, we knew, structurally, the existing building could only hold three storeys of concrete structure. Our team of structural and materials engineers underwent calculations on different materials to understand the most cost-effective and sustainable solution: a steel frame structure with cross-laminated timber (CLT) floor plates. This approach created a circa 70 per cent embodied carbon saving compared to a reinforced concrete equivalent.

Designing 12 storeys on top of an existing building requires careful design alignment to balance the weight each building section carries. We designed the new building to fit the existing building structure by designing sloped load transfer beams connecting both buildings supported by a diamond-shaped steel bracing system on the outside of the building. The result is an elegant engineering design that balances the building’s load without adding extra mass to the design. 

While CLT is light enough for an existing building to carry, by nature, the material’s low density makes it more prone to vibration. Our team designed the base build with in-floor dampers – usually only installed in a building’s fit out. Like a shock absorber in a car, the dampers stabilise the building by controlling floor vibrations, building displacement and keeping people comfortable and safe in the event of seismic activity.

Watch the video to find out more on the design challenges and solutions of WS2

Mechanical engineering

A plant room can be described as a building’s engine – it contains the mechanical, electrical and plumbing infrastructure which caters for the entire building. It’s also the most energy and carbon intensive areas of a building. WS2 does not have a main traditional plant room – instead it shares one with its neighbour Westralia Square I. 

Early in the design, our team identified a unique opportunity to design Westralia Square II without a plant room and instead connect to Westralia Square I plant room and use the building’s spare capacity. However, the building also needed to perform at a high standard and meet ambitious environmental ratings for energy efficiency, occupant comfort and wellness.

To do this, we needed to study the building’s spare capacity and analyse this carefully to understand how we could augment the base build system and upgrade existing infrastructure, such as switching systems, to cater for both buildings. This process required close cross-collaboration with engineering disciplines and trade-offs between systems design and system selection to ensure the existing capacity was not compromised.  This approach created a significant capital expenditure cost saving for and maximised use of space in the new building. It also resulted in an embodied carbon saving, reducing the carbon associated with constructing the building. 


From day one of construction, we have aimed to reuse all building materials. Every piece of cross-laminated timber has been reused creatively to form raised platforms to strengthen the floors. As part of the construction process, every aspect of the build was designed to fit in the goods lift, eliminating the need to use a crane. 

Our approach to adaptive design and material reuse when compared to demolition and designing a similar building made from concrete, we have saved approximately 70 per cent in embodied carbon.