By staff reporters
5 June 2014 — Developers want the NSW government to get rid of barriers to putting super tall and mega tall buildings in Sydney’s CBD, envisaging Sydney in 2050 with buildings double the height of current skyscrapers and tens of thousands of workers living and working in the city. But just how sustainable are tall buildings, particularly in the residential context? And is high density the way Sydney should go to limit the economic, social and environmental effects of urban sprawl?
The vision for Sydney
Urban Taskforce’s Chris Johnson has a vision of Sydney’s CBD with double the current skyscraper height with tens of thousands of people living and working in the CBD.
He said current planning rules were out of date, and buildings should be able to go well beyond the 309-metre Sydney Tower.
“Currently Sydney claims to be Australia’s only global city and the centre of financial transactions but Melbourne and Brisbane are beginning to challenge this position,” he said. “Already both of our neighbouring cities have higher buildings than Sydney and fast forward to 2050 and both Melbourne and Brisbane could become the global financial hubs that Sydney is now.”
The Urban Taskforce recently held a breakfast where designs from Sydney architects were revealed to show visions for Sydney in 2050.
Richard Francis-Jones of Francis-Jones Morehen Thorp envisaged a balance of open space and density supported by a “green network” that would also let in winter sun and protect from winds. As part of its vision, a suspended green sky park would stretch across the harbour bridge and the Bradfield Highway.
Bates Smart director Philip Vivian said that its vision for a Sydney was a balance between sustainability and economic development. Super tall building development had to fund a sustainable transport system, he said, proposing a metro to service Sydney’s inner ring.
Mr Vivian said the economic uplift of additional floor space could be provided through the purchase of super tall floor space area from the NSW government, which could reap $7.1 billion for a metro system.
James Fitzpatrick of fitzpatrick+parners said Sydney’s disparate centres needed to be linked by foot, ferry, bike, light rail and metro.
The city was bounded by water and parklands so just intensifying the CBD was not an option – we needed to build up and connect other centres, including Woolloomooloo, North Sydney and White Bay.
Mr Johnson said the symbol of a global city was the high rise tower, that Sydney was the ideal place for this, and that height was “a metaphor for a sustainable city”.
To answer the question of how sustainable tall buildings are in the residential context, and whether the benefits of building up and limiting urban sprawl can overcome the extra materials and energy needed for such large structures, we decided to ask some experts.
Alan Pears: a number of tradeoffs
RMIT sustainability expert Alan Pears explained that one of the issues with tall buildings is that as height increases, the material (and floor area) used increases disproportionately, as greater strength is needed.
There is also a reduction in available floorplate for actual dwellings due to space required for plant, lifts, fire stairs and other building services. There is often also a need for more common area lighting, which increases base building energy use.
“Also, the roof area available to generate renewable energy on-site per dwelling reduces – although as PV costs fall, use of walls and PV-integrated shading may offset this,” Mr Pears said.
“Then there is the shading impact on other buildings: in summer this may be good, but not necessarily in winter.
“Certainly when you have an apartment building, in principle you have much less external surface area per unit of floor area, so it is possible to design for zero heating, but they will need some cooling – but not much if they are well designed.”
Tall buildings may also strengthen the focus on water and energy efficiency. Pears noted that in many infill locations the existing services infrastructure may have limited capacity for increased supply and demand in terms of water.
“Relative to detached houses, water usage and waste flows per dwelling are typically lower for apartments. Certainly some water pumping would be needed for a tall building. There may be limits on infrastructure capacity in localities, but this would depend on utility design,” he said.
“The same concern could be raised about energy. For both energy and water, in infill projects limitations on infrastructure could create an incentive to include strong energy and water efficiency measures and do onsite water treatment, onsite energy generation and storage to stay within the capacity limits of the existing infrastructure. So it’s really a cost issue.
“Having a lot of people and activity means the economics of water treatment, biogas from waste, cogeneration etc. can be a lot better than separate houses.”
In overall terms, when comparing the energy footprint of the average detached dwelling to a high rise apartment, Mr Pears said there are tradeoffs.
“As height increases, lifts in particular use more energy and occupy more floor space. If you were doing a precinct scale high density approach, cars should not be allowed into what should be a pedestrian/low speed vehicle area. So parking facilities would need to be provided on the fringe of the area, and people would travel to their cars using local transport options. Again, it’s really about how energy efficiently you provide services and cost relative to sale price.
Mr Pears said cross ventilation was also usually a challenge in apartment building.
“Openable windows [in tall buildings] would have to be carefully designed, but I have visited an apartment in Melbourne’s Eureka Tower that had small openable windows [however] the traffic noise from below was pretty bad,” he said.
In terms of ensuring the building envelope is thermally efficient, Mr Pears said that while all the usual features of any building function the same way, components such as insulation, for example, require upgrading to adjust for the more extreme climate at heights.
This adds to the other increased materials considerations such as ensuring the structure can withstand wind loads and remain watertight.
Mr Pears said the emergence of new materials and construction techniques, such as relatively tall timber buildings like Forte at Docklands, offer potential to reduce the embodied energy of materials, as do fibre-reinforced concrete, high strength steel, low emission cements, wood foam and net zero emission bricks.
Neighbourhood context is important
One of the positives of tall buildings Mr Pears identified is that when buildings are well-located, transport energy use is likely to be reduced and shifted from cars to walking, public transport and other low-carbon options. This is also important, he noted, to reduce the likelihood of congestion if all the occupants tried to use cars.
Super tall buildings, while saving space, also needed outdoor space for residents too.
“A key issue for higher density development is provision of high quality outdoor space. This tends to undermine the space saved by taller buildings, but it is critical for amenity,” Mr Pears said.
“I think we can learn a lot from existing high density communities about how you address the practicalities of life and allow for people to have kids, pets, amenity and so forth.
“Again, I’m not arguing for high rise as a solution. I suspect a lot of Australians would prefer medium-rise if it is done well… But the thing is, whatever solution is adopted, it needs to respond to community requirements.”
High-rise offers exciting opportunities for synergies, says Lester Partridge
AECOM global director advanced design and applied research building engineering Lester Partridge, who is on the technical and advisory expert panel for the Council of Tall Buildings and Urban Habitat, told The Fifth Estate that high-rise residential on average used more energy than low rise development.
He pointed to research the NSW government had done that demonstrated that because of common area services, lifts, centralised exhaust, under bank car parks, swimming pools, high rise more often than not used more energy. Malaysian architect Ken Yeang has said that tall buildings as a built form consume one-third more material and energy in construction, operation and demolition than low-rise and mid-rise buildings.
However, Mr Partridge said this was looking at the issue on an individual building basis, and when you started to look at sustainability in tall buildings, you had to take into account the precinct.
Buildings can’t simply be seen as a standalone element, he said, but as part of an urban system, and building in the city conferred many benefits, including reducing urban sprawl and the amount of cars needed on the roads, leading to less congestion, pollution and the associated productivity benefits.
Mixed-use tall buildings, which incorporate commercial office space and residential, also opened up a number of exciting synergies.
For example, waste water from residential could be purified to then be used to provide Grade A water to commercial offices. And buildings that had their own centralised cogeneration/trigeneration systems would be able to reduce plant size as the peak demand for residential and commercial were staggered, leading to more efficiency.
Clustered buildings offered the opportunities for district systems too. The City of Brisbane, for example, is researching the possibility of a district cooling system for its CBD.
- See our article Brisbane CitySmart taking the lead on CBD district cooling
Mr Partridge said that sustainability needed to be looked at holistically, connected to transport hubs and done on a precinct scale with precinct energy, waste and water systems, which would see potential additional savings.
“We need to develop policies that promote and encourage the use of district and precinct systems,” Mr Partridge said, noting that many building owners were averse to the idea, as it locked them into contracts, reduced flexibility and many buildings already had systems servicing their buildings with plenty of life left.
“Technically it’s not difficult; it’s more the commercial issues that need to be resolved.”
Don’t forget medium density, says Professor Peter Newton
Professor Peter Newton, research professor in sustainable urbanism and research leader, CRC for Low Carbon Living at the Swinburne Institute for Social Research told The Fifth Estate that while brownfields high density developments have a role in delivering housing, he believes there are neglected possibilities for medium density developments to replace some of the aging residential stock of the middle suburbs.
He terms these “greyfields” developments, in contrast to the former industrial or commercial land of brownfields developments, with their frequent site contamination issues, and greenfields developments on the suburban edge, which contribute to urban sprawl.
“This aging residential stock [of the greyfields] is technologically obsolescent and environmentally poorly performing,” Newton said.
“It is an underutilised economic asset, but it is occupied.”
His research has established there are perhaps 350,000 dwellings in Melbourne where 80 per cent or more of the property value is in the land, rather than the dwelling. These, he said, are the areas where replacing single dwellings with medium density residential developments could deliver enormous sustainability gains, particularly if approached on a precinct scale.
“The targets for infill developments [to address housing demand] are not being met,” Professor Newton said. He noted that in Plan Melbourne, for example, there is a focus on high rise developments around activity nodes and also transit oriented developments to increase residential density along arterials.
“I have argued that both [of these kinds of developments] are necessary, but they are not sufficient to meet demand. Greyfields precinct regeneration needs to occur.”
“Cities have an urban fabric and a suburban fabric, and the suburban fabric is majorly car dependent. Transport is a challenge to greening the suburbs.”
One of the advantages of the greyfields zone, according to some of Professor Newton’s published research, is it sits in the zone between the inner urban and outer suburban and therefore often has well-established and effective public transport. This enables medium density developments in this zone to have reduced car dependence.
He and his colleagues have also modelled concepts such as precinct-wide design where a group of former single dwelling house blocks are converted into a medium density project comprising grouped buildings of two to three storeys with shared green space and parking located at the edge of the precinct.
His current research project being carried out with the CRC for Spatial Information, “Greening the Greyfields”, will locate where the areas are of detached dwellings that are appropriate for precinct redevelopment. The project will also develop the necessary tools for developing community engagement, design, and development which can transform these parcels into medium density housing.
“There are models for greenfields and brownfields development, and for greyfields, the knock down-rebuild model exists, but it usually results in the replacement of a single dwelling with another low density development,” Professor Newton said.
For Professor Newton, the goal is “regenerating a city that was put down 60 years ago and developing better environmentally-performing housing”.
These elements of improved environmental performance include zero or low carbon energy performance at both a building and precinct level, and water sensitive design. Both of these, he said, are among the things which can only be effectively achieved at a precinct level.
“In terms of decarbonising housing, solar photovoltaics, ground source heat pumps, cogeneration and wind [are all effective] options. The outer suburbs have really responded to PV,” he said.
“There is a challenge to PV in high density or medium density residential developments, and there is a more challenging task in decarbonising higher density by precinct-based [renewable] energy generation and distribution. You just can’t put enough PVs on a high rise to meet the needs [of residents].”
There is also a human consideration to the question of high rise, which is whether all people actually like it or find it suitable for their needs and lifestyles.
“High rise doesn’t suit everyone,” Professor Newton said.
“With medium density developments you can appeal to new households, small households, downsizing households and families.”
One of the key points in the greyfields concept’s favour, is the ability to mix styles of housing within a precinct – townhouses, apartments, and studios, for example – and deliver a result which lays the groundwork for meeting the needs and tastes of a diverse community.
A key consideration is the highly urbanised nature of Australian settlement, which makes the performance of the urban environment critical to the sustainability of the wider landscape.
“If you look at sustainability in the 21st century, it will be delivered out of cities by regenerating cities,” Professor Newton said.
“It won’t be achieved by allowing [projects] to develop in a piecemeal fashion. That’s the challenge I have been working on.”