DTCE was engaged to provide the structural design for alterations to an existing three-storey residential building that had previously been strengthened to 80% NBS. The project focused on reconfiguring the second floor to introduce a new bedroom and a kitchen area, along with a new attic space above.

To achieve this, new light steel framing was introduced for the internal walls, with a new attic floor constructed above the space. Due to limited roof height and the configuration of the existing rafters, the attic floor joists were designed in a stepped arrangement to fit within the available structure. The floor system is supported by a steel frame and structural walls, allowing loads from the attic to be transferred directly to the building’s primary structure without overstressing the existing floor joists below.

Because the attic space is accessed only by ladder and has limited head height, it was designed for light loading, with the floor engineered accordingly. A netting safety barrier system was also introduced at the attic edge in place of a conventional balustrade. DTCE designed the supporting steel posts, rails, and connections to safely integrate the proprietary system with the existing structure.

A review of the building’s seismic performance confirmed that the additional structural weight from the new framing, attic floor, and finishes represents less than a 1% increase in seismic demand, meaning the previously achieved 80% NBS rating remains unchanged.