55 Southbank Boulevard was a six-storey concrete framed commercial building built in the late 1980s in central Melbourne. The design challenge was to extend the existing building vertically to deliver a hotel with 220 rooms without overloading the existing foundations. Using the latest in timber construction technology allowed for an additional 10-storey CLT (cross laminated timber) hotel to be built on top of the existing structure.
This was achieved by combining new technology with traditional steel/composite construction methods. CLT wall and slab panels, which are significantly lighter than concrete, were used for framing the new hotel levels. Steel was used for stability, strengthening the existing structure and a composite transfer floor designed to distribute load from the new structure to the existing columns.
The lightweight construction meant more storeys could be added compared to RC floors and the prefabricated panels meant quieter and quicker construction with less disruption to the existing tenants occupying the building during construction. The sustainability benefits of using CLT are that the timber floors sequester several tonnes of CO2 emissions and repurposing rather than demolishing the existing structure reduces demolition waste and saves on additional building materials.
The final structure will be one of the tallest timber structures in Australia. It demonstrates the opportunities to enhance the value of existing buildings with sustainable design and the potential of timber for tall building construction in the future.