the podium and cloud apartment buildings use various materials accordingly to their characteristics. pre-cast concrete, white metal balconies and the matte appearance ties the podium to its urban surroundings, streetscape and city environment whilst the reflective, shiny façade and white curtain wall system of the cloud emphasises the floating design. the use of mirrors applied to the supporting columns and under croft of the observatory also highlight the effect of a cloud-like structure. originally a pre-cast bearing wall design was to be used in the cloud apartment but the proposal switched over to concrete plates as the load bearing wall design exceeded the requirements significantly. circular columns are used to support the cloud apartment, with a transfer beam used on top in order to canter lever the structure. pre-fabricated and powder coated balconies were sleeved into the openings, projecting over the street with the cloud's balconies protruding at lengths up to 3 metres. the joinery within each unit which includes the bench, kitchen, table, etc. is pre-fabricated and shipped over from china. upper house features a single central staircase, despite the unconventional lone staircase, the safety met the metropolitan fire brigade requirements. all of the corridors are smoke vented, with smoke pushed out of louvres during a fire, in addition the corridors are also pressurised and sprinklers cover the entire building.