The world’s most tallest mass timber vertical extension. The 55 Southbank Boulevarde project was conceived to optimise the site potential by constructing ten (10) storeys of premium hotel accommodation atop an existing reinforce concrete office building structure. The original concept was to extend for six (6) storeys adopting traditional construction methods. The answer to address the structural limitations of the existing building was to go with lighter mass timber construction methods to push the extension to ten (10) storeys. A showpiece for natural and new, the Cross Laminated Timber (CLT) made it possible from the start and has unlocked the value in projects that simply was not possible before. The successful authority approvals process included engagement with the Fire Rescue Victoria (formally MFB) and detailed Fire Safety Engineering submissions to the Victorian Building Appeals Board (BAB). 55 Southbank is the result of detailed collaboration between the builder (Atelier Projects), the structural engineers (Vistek) and the architects (Bates Smart). The project and adoption of CLT construction technology highlights how construction can be done and offers new property development opportunities. The project construction was completed in August 2020.