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In safe airspace? Skyscrapers of the 21st century

Since the turn of the century, the average size of buildings in global cities has increased exponentially. According to a report from the Council on Tall Buildings and Urban Habitats (CTBUH), 84% of buildings over 200m tall were built after 2000, and in particular following the global impact of the catastrophic terror attack on the World Trade Centre in 2001.[1]

CTBUH has upgraded its definition of ‘tall buildings’ throughout this period, with 200 m+ building referred to as ‘tall’, 300 m+ as ‘supertall’ and 600 m+ as ‘mega tall’.[2] The fast increase in the height and number of tall buildings is an evolving challenge for the design and regulation of cityscapes.

We examine how this trend is impacting on Australia’s urban habitats, as well as analyse the challenges for airspace regulation.

Growth of Australia’s skyscrapers

Tall buildings in cities have been historically driven by increasing urbanisation in major cities and the maximisation of commercial space in central business districts. One of the most iconic tall buildings in Australia, the Centrepoint Tower in Sydney, turns 40 this year.[3]

As at April 2021, the five tallest buildings in Australia[4] were:

1. Q1 – Gold Coast: 322.5m;

2. Australia 108 – Melbourne: 316.7m;

3. Eureka Tower – Melbourne: 297.3m;

4. Crown Sydney – Sydney: 271.3m;

5. Aurora Melbourne Central – Melbourne: 270.5m.

Against CTBUH’s metric for tall buildings, Australia currently has 2 ‘supertall’ buildings.

The Urban Taskforce, a non-profit organisation representing prominent Australian property developers In the urban design history, has called for a future full of skyscrapers in the Sydney CBD skyline. By doing so, it states the city would maintain its reputation as a global hub going forward, as domestic counterpart cities in Melbourne are proposing taller buildings to lift their global standing.

An example of the design schematics proposed by Urban Taskforce designer Richard Francis-Jones is displayed below, with proposed high-rise developments within the solar access plane, with the development contributing to ancillary features such as green parks across the Harbour Bridge.

As high-rise buildings become taller, their design becomes influenced by certain behavioural factors which are much less significant for shorter buildings. These include:

1. The dynamic response of tall buildings to wind loads;

2. The axial shortening, or compression, of load-bearing elements that support the structure of high-rise buildings; and

3. The overall slenderness of a tall building, as defined by its ‘height-to-base ratio’.[5]

However, one of the significant planning components that is often missed from discussion around high-rise buildings is the affect on airspace regulation for cities of the future. This is particularly relevant under the Greater Sydney Region Plan – ‘A Metropolis of Three Cities’, which forecasts growth of three ‘cities’ in the Harbour CBD, Greater Paramatta and Greater Penrith. High-rise building growth in these areas will impact on further flight paths and air space regulation.

The above image shows the forecast for urban sprawl and consolidation in the ‘three cities’ plan for the Greater Sydney region. Notable in this plan is the inclusion of Western Sydney Airport, which will draw a significant volume of air traffic over Sydney’s urban centres, and which will need to be a consideration by high-rise developers.

Airspace Regulation

For background on airspace regulation in Australia, please see our previous article on Airspaces Restrictions in Australia – The Ultimate Guide.

In accordance with the plans for growth in the Greater Sydney region, the Draft Greater Sydney Region Plan 2017 specifically references protections for airspace in the context of further development:

protecting prescribed airspace from inappropriate development, for example height of building controls that would allow buildings to penetrate prescribed airspace and reduce the capacity of existing airport operations[6]

As Sydney expands, high-rise developments must accord with the geographical context in the region. The 83km radius of Sydney Airport is already one of the busiest and most complex volumes of Australian airspace, according to a report by CASA in 2015[7]

In the case of the Crown Sydney building described above, Avlaw undertook an Aeronautical Impact Assessment and Safety Case and concluded that the proposed development would not affect the safety or operation of aircraft at Sydney Airport. Similar studies and assessments will be required for high-rise developments in the Greater Sydney Region. In particular, the new Western Sydney Airport will require airspace studies for surrounding development prior to the commencement of the airport’s operations and eventual flight path design currently being developed by the Department of Infrastructure and Regional Development.

Under the Airports Act 1996 (Cth) and the Airports (Protection of Airspace) Amendment Regulation 1996 (Cth), development that infringes on protected airspace of the Western Sydney Airport will require approval. This can be done as part of the Application process, or as part of a referral from a consent authority, if the development is deemed a ‘controlled activity’. LGAs which could be affected by these regulations include: Penrith, Blacktown, Fairfield, Liverpool, Campbelltown, Camden, Wollondilly and Blue Mountains.

Growth in high-rise developments in these areas is already occurring, with a recent Planning Proposal to the Penrith Local Environmental Plan 2010 to facilitate high-rise development being deferred in April of this year.[8] Whilst further amendments are made to the Proposal, it signals a strong demand for high-rise developments in areas which will be subject of future airspace controls, and for which consideration must be duly had.