25 King

Lendlease (the developer) and Aurecon (the engineers and anchor tenant) wanted a building that visibly expresses sustainability and engineering, while providing a creative workplace that also enhances the health and wellbeing of its occupants. The opportunity arose to explore a timber structure to create a unique commercial building within the Brisbane office market. Timber has not often been considered for mid- to high-rise commercial buildings in Australia, as commercial buildings typically don’t have as many internal walls to provide structural support. However, recent engineered timber innovations meant that the challenge of creating a unique commercial office building could be achieved.

25 King represents a viable return to timber design and construction, pushing architects to think beyond concrete and steel commercial solutions. The building employs a simple, 6x8 metre system of Glulam beams and columns and cross laminated timber (CLT) floor planks and core walls to support a flexible floorplate. Short spans adjacent to the core and façade allow major services to reticulate without compromising floor to floor heights. The building expresses the floorplates and use of timber through its glazed transparency, street level timber colonnade, and interior warmth, which was created by leaving the wood and other raw materials exposed.

25 King delivers positive social, commercial and environmental impact: • Social: The interior office environment glows with the exposed timber structure’s warmth. The use of natural materials better connects occupants with nature, fostering a happier and healthier workplace. • Commercial: This is not an experimental or demonstration project, but rather a commercially viable alternative to steel and concrete construction in office buildings. It is also the first timber commercial mid-rise building in Brisbane, setting a new precedent for the city. • Environmental: The design achieves 74% savings in embodied carbon, when compared to a comparable steel and concrete building, minimising its environmental impact.

Constructing a timber commercial building requires rethinking standard project delivery practices and timber’s inherent structural limits. Early documentation is necessary to enable prefabrication, requiring a very different approach to resolving the design, coordinating procurement and services, and finalising details ahead of construction, as it is difficult to make onsite adjustments. In terms of the material limitation, the shorter structural spans and increased number of columns reduce the wide spans traditionally expected in commercial floorplates. To overcome these parameters, the structure has a 6m span of CLT floor planks supported on Glulam beams. The 6m span is efficient in terms of span to depth ratio of the floor plank. The smaller size of the elements also makes them easier to transport and handle on site. The Glulam beams span 8m between columns. The depth of the beam allows for structural penetrations that are sized to the distribution of services. Two shorter spans—one adjacent to the core and the other on the perimeter windows—create shallower structural depths to allow for the lateral distribution of large service ducts. This combination of efficiencies allowed the creation of a tall timber building with flexible floorplates that will appeal to a range of tenants.