Density Vs Sprawl: which wins for sustainability?

To some, compact urban environments offer advantages in putting greater numbers of people within walking or riding distance of transport connections, employment opportunities and local services.

To others, density leads to congestion and poor environmental outcomes because of the difficulty in creating high-rise stock which is as energy efficient.

That raises questions about whether high-rise environments or more widespread urban forms are best for the environment. Recent research from Dr Anthony Wong and Dr Peng Du, executive director and China office director and academic coordinator respectively of the Council of Tall Buildings and Urban Habitat (CTBUH), has helped to shed light on this.

This article from Sourceable looks  at this issue from an Australian perspective.

As part of their two-year Downtown High-Rise Vs Suburban Low-Rise Living study, Du and Wood examined the lifestyles, movements and energy bills and usage of 249 households living in high-rise towers in the City of Chicago and equivalent data in respect of 273 households residing in the suburb of Oak Park, 11 kilometres from the CBD.

The results were mixed.

On the positive side for high-rise, suburban environments required eight times the infrastructure network length compared with denser suburbs. Compared to their low-rise counterparts, meanwhile, the average resident in high-rise apartments consumed less water (73 per cent as much as low-rise consumption), took fewer ‘separate’ journeys (92 per cent of those of low-rise residents) and walked and cycled almost three times as much.

Nevertheless, there were negatives. Compared with their suburban equivalents, the study found that downtown high-rise residents consumed 27 per cent more electricity and gas – albeit with this difference narrowing to 4.6 per cent on a square metre basis. On a square metre basis, high-rise environments also required around one and a half times the volume of energy to build (72 per cent more on a per-person basis). Contrary to popular perceptions, high-rise residents were slightly more likely to own a vehicle compared with their suburban counterparts and travelled further in these vehicles by nine per cent.

Finally, ideas about compact environments delivering social benefits warrant caution. According to the CHBTU study, suburban residents in Oak Park felt nine per cent more connected to their community compared with their high-rise counterparts downtown.

These outcomes, Wood observed, were ‘surprising to us all’ and ‘quite the opposite of what we thought we would find.’ Whilst there had been a presumption that density and verticality was beneficial, Wood said such ideas had never been thoroughly tested. Many studies in the past, he observed, have been generic studies based upon large sets of generalised data which lacked specific focuses.

Granted, age and income levels may have affected the data presented. Moreover, outcomes outcomes overseas may not directly apply to Australia.

Some data does exist for Australia. In 2005, for example, a study by then Energy Australia senior consultant – demand management Paul Myors looked at the average greenhouse gas emissions for occupants across a range of housing types across Sydney. It found that whereas the average person in a detached house emitted only 2.9 tonnes of carbon dioxide each year and those in townhouses and villas scored better yet at 2.1, this number jumped up to 5.4 for high-rise apartment occupants. Primarily, the authors put this down to the relatively low occupancy rates of apartments compared with detached housing and energy consumption which occurred across common areas such as elevators.

So is high-rise building good for the environment? According to Professor Brendan Gleeson, an urban planner and director of the Melbourne Sustainable Society Institute, the answer is no.

Referring to evidence from post-occupancy surveys such as the one above, Gleeson said positive environmental performance from high-rise was difficult to achieve. As well as the embodied energy expended during construction, he says high-rise buildings are difficult to ‘hard-wire’ with sustainability features which limit their energy and water consumption. In high-rises, for instance, it is difficult to deliver cross ventilation, making such buildings highly dependent upon mechanical air-conditioning.

Having high concentrations of buildings dependent upon air-conditioning, he added, creates problems where extreme weather events cause power outages. During the Brisbane floods of 2011, for example, air-conditioning as well as other building services such as lifts, running water, fire alarms, security systems ceased to operate when power was disconnected to buildings and neighbourhoods in anticipation of rising flood waters.

All this is being exacerbated, Gleeson says, by weaknesses in building control regimes which have allowed, for example, combustible cladding to be put on large numbers of apartment buildings.

As for arguments about high-rises generating greater social capital and belonging, Gleeson says there is little evidence to support this. Moreover, he says, high-rise development has inherent weaknesses from a social and governance perspective, and has resulted in cases of friction and owners corporation disputes.

Whilst acknowledging that sprawl has its own issues, he says these can be addressed through planning and design of outer urban environments. Indeed, he says, much of the answer to this lies not in urban consolidation but in polycentric environments involving more widespread employment in well-designated suburban areas.

He says the push toward high-rise is largely being driven by economic considerations such as land costs.

“I think the evidence suggests it is almost impossible to get acceptable environmental performance out of high-rise buildings,” Gleeson said. “In very specific and expensively designed circumstances, it can be more possible but it’s really hard work.

“Generally, the volumetric redevelopment that we are doing in our centres and increasingly in other parts of our city are taking us backwards in terms of sustainability.

“Under any scenario, I think high-rise is the wrong way to go.”

Speaking from a perspective of public health, meanwhile Dr Neil Coffee from the University of Canberra says well-designed density offers benefits in terms of greater accessibility to local services and greater abilities to walk or ride to transport links or other important places. For sustainability, he says this offers benefits in terms of a lower reliance upon cars.

That said, he says it is important that density is done well. This includes ensuring that streets are safe and pleasant to walk in and that there is a good variety of open public spaces.

Beyond issues of density or sprawl, both Gleeson and Coffee say we need better population management (in the year to June 2017, the Australian population increased by 388,100 or 1.6 per cent.)

Whilst stressing that he is not condoning an anti-population stance, Gleeson says the rate at which Australia is admitting new people is unmanageable and we cannot rewire our cities fast enough to cope with this. The upshot, he says, is that we spread poorly designed estates out onto the suburban fringes.

Coffee echoes broadly similar sentiments, suggesting Australia needs a population policy to define what our population will be and how it will be distributed. By not doing this, he says we are failing to deliver a system which is functional across Australia and we have moved into a situation whereby an excessive burden of catering for greater population growth falls upon our major capital cities, especially Sydney and Melbourne.

This, he says, puts pressure upon natural resources. In Sydney, for instance, he says the last major water storage project was Warragamba Dam which was completed in 1960. As Sydney’s urban population continues to grow, he asks how will the extra demand upon water and other resources be met.

Meanwhile, whilst there was some effort at consolidation, Coffee says much of the population increase in Melbourne was being accommodated through putting growing numbers of people in greenfield areas such as nearby the airport. This, he says, will necessitate growing volumes of travel through cars and buses – poor for both health and sustainability.

He says Australia throughout the 1970s and 80s missed an opportunity to develop smaller cities.

“Because we don’t have a view about what Melbourne and Sydney will be, we seem to have this view that we will just keep growing them forever,” Coffee said. “I’m not sure that this is sustainable.

“I look back historically and I wonder whether we missed a great opportunity in Australia in planning our urban form to come up with something which was better suited for health and sustainability and long-term for Australians full stop.”

It should also be noted that urban sprawl is also having a sustainability impact in terms of the loss of valuable agricultural land.

In Melbourne, for instance, the University of Melbourne suggests that by 2050, a combination of population growth and the gobbling up of land within the inner and outer foodbowl because of urban encroachment means that the Greater Melbourne area will grow from meeting 41 per cent of its overall food requirements now to 18 per cent by 2050.

Article sourced from Sourceable

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