100 Mount Street North Sydney building, looking upwards along the exterior facade; 100 Mount Street North Sydney building, looking upwards along the exterior facade;

100 Mount Street North Sydney, New South Wales

A centrepiece in North Sydney's revitalisation

Centrally located in North Sydney’s CBD, 100 Mount Street brings to life Sydney’s growing north-side business district with a clear focus on activating the public domain. The 35-storey office tower’s cross-braced exoskeleton structure has also become an impressive feature on the skyline, with customers treated to panoramic views from Sydney’s iconic harbour across to Ku-ring-gai Chase National Park.

Developed by Dexus in collaboration with engineering and construction firm Laing O’Rourke, and designed by Skidmore, Owings & Merrill (SOM) and Architectus, Arup was engaged to provide building services, civil, waste, acoustic, fire safety and specialist lighting design services. 

Our multidisciplinary team worked in close collaboration with architects and structural engineers to develop premium quality office space with a focus on maximising daylight, open space and views, while also improving public amenity and targeting 5 Star Green Star and 5 Star NABERS energy ratings. 

100 Mount Street’s integration with the public domain purposefully celebrates North Sydney Council’s longer-term vision for a lively community realm that encourages more pedestrian activity and greater use of public transport. The building is a centrepiece in North Sydney’s revitalisation, close to the future metro station and the existing rail station.

Collaboration between Arup’s building services team and the project’s structural engineers saw the realisation of impressive 2.85m floor to ceiling heights with 3.05m at the north and south façades. The showcase double height penthouse office on level 35 - complete with a striking rooftop terrace - features double height glass walls and an openable roof system fitting for the locale, views and tenant comfort in the premium commercial development.

Project Summary

8 years in the making

35storey building

Fire stairs take pride of place 

Usually hidden away for evacuation-purposes-only, the fire stairs at 100 Mount Street defy typical; they’ve become an eye-catching architectural feature and a primary way of travel through the building. The fully glazed fire escape stairwells run the height of the building’s side core and enliven the glazed façade.  

The stairs were engineered into the project from day one, with Arup’s fire engineers working closely with our fire services engineers, the building certifier and fire brigade to simultaneously deliver the architectural vision and ensure the safety of occupants and attending fire authorities. 

Drencher type sprinklers ensure the internal glass is kept in place during a fire and a fire rated glass door completes the enclosure. Water demands were calculated to allow the on-floor suppression system, the window drenchers and hydrants to all work simultaneously. Fire spread into the stair was also assessed from external fire source features (adjacent buildings) or other areas within 100 Mount Street. 

The team has delivered a remarkable building that contributes so much – not only to those who work in the building every day, but also for the public who live in and visit North Sydney’s CBD area. The views across the harbour are world class. ”

Janine Pickering head shot Janine Pickering Associate

Pedestrian-friendly connection to ground level

At ground level, the building welcomes people with an open, double height foyer. The restaurant, bar and retail are popular gathering places for the office and the broader local communities.

Arup’s civil engineers helped to deliver wider footpaths on Mount Street to improve pedestrian amenity and discourage vehicular movement in this largely pedestrian-friendly part of North Sydney. The exterior spaces offer high quality finishes which have been carefully considered in keeping with North Sydney Council’s public domain manual. Arup closely integrated the finished levels surrounding the development with the building’s finished floor levels and entrance design. These two features facilitate easier pedestrian access despite the naturally steep gradients surrounding the building. 

The documentation process was one of the smoothest and most collaborative I have been involved with since BIM became standard. The whole team embraced the process and worked to deliver 3D models that enhanced Laing O’Rourke’s programming and construction processes. The human factor is often overlooked in the BIM world, but this project proved that great relationships help to deliver a great project in a smart and smooth manner. ” Andrew Beazley Senior Engineer

Fresh air to each floor

To create greater air-conditioning control for customers and to reduce core size, Arup employed an on-floor air handling system. Multiple smaller plant rooms deliver fresh air to individual floors rather than one larger plant serving several floors. 

Our acoustic specialists worked alongside our building services engineers to ensure no-one working in the office would experience sound or vibration from the on-floor systems. With the building able to be commissioned on a floor-by-floor basis, tenants were able to move into their new homes more quickly.

Sustainability features 

The floor by floor air conditioning approach also allows efficient out of hours operation. Only those floors and areas of the floors requiring conditioning are operated, so large central air handling systems do not need to function on the occasions when usage is low. The closed cavity façade enhances energy performance while the building’s orientation and positioning allow it to operate with the blinds open for extended periods maximising the views along the length of the harbour. 

The rainwater harvesting system collects roof, canopy and podium run off for reuse in the cooling towers minimising potable consumption and the fire systems are configured to reuse test water minimising waste.

Virtual design boosts efficiency

Arup’s team embraced digital ways of working, improving the entire program’s efficiency by completing and delivering all designs in REVIT and enabling engineers to work directly in the 3D model. A series of Virtual Design Reviews led by Arup saw all design stakeholders involved in the live coordination process. This proactive approach towards collaboration in REVIT meant designs were solidified early on and Laing O’Rourke could accurately model its bulk excavation works, incorporating footings and trenching early, enabling accurate costing and programming. The collaborative design environment saw the team deliver high quality documentation and models in a shorter than average timeframe.

All images © Brett Boardman