The carbon devil in the detail on urban density

High-rise residential developments have been springing up in all Australia’s major cities. The view that carbon constraint, ecological protection and liveability can only be achieved by remodeling our cities at high-rise densities has taken root among much of Australia’s policy intelligentsia. This view is inconveniently flawed.

Most people agree climate change should be understood through robust scientific evidence. Such a standard should also apply to measures to reduce the climate impact of our cities.

Unfortunately a simple formula equating high-rise urbanism with low carbon or ecological impact finds at best partial confirmation in the scientific literature.

When different building scales are compared on objective environmental criteria the evidence suggests that high-rise apartments are often the worst performers. The building scale with least overall ecological impact – measured in energy, CO₂ and water use per capita – tends to be medium-rise of between three to six storeys, with individual detached dwellings the next best.

Alan Perkins and colleagues' work in Urban Policy and Research, for example shows that on per-capita analysis, attached low-rise dwellings perform best in terms of CO₂, with suburban and high-rise successively worse.

Such patterns arise because any valid assessment must account for all energy use. This includes energy “embodied” in a building during construction, plus energy used in ongoing operations.

While residents of detached houses use high levels of energy to get around, because of their greater car reliance, their overall energy use per capita tends to be lower than high-rise residents. This is because detached dwellings can consume less embodied and operational energy and that use is divided among a higher average occupancy rate (detached dwellings generally house more people than apartments).

The relationships between building type, urban form and CO₂ emissions become even more complex when income – or “lifestyle” – factors are included in the analysis. But it seems that high-rise urbanism exacts a high carbon cost.

The Australian carbon consumption atlas, prepared for the Australian Conservation Foundation by Chris Dey of the University of Sydney and colleagues, provides a striking illustration of this pattern.

Their work shows the highest per capita residential environmental consumption occurs in the higher density inner urban areas of Australian cities. The 37 tonnes of total CO₂ consumed per person each year by downtown Sydney residents is, for example, more than double the 16 tonnes produced by residents of Blacktown. There’s a carbon devil in the detail on density.

Such findings fundamentally confound the simple “high density good, low density bad” assumptions in current debates. High-rise apartments are far less of a solution to our urban environmental challenges than the prevailing consensus suggests. Even if better design could improve high-rise performance, so too could it improve that of other building types.

Some look to New York City as a model for Australian cities. But high-rise Manhattan is a small island set among a continuous interconnected urban mega-region of some 21 million inhabitants, only some of whom live at high densities.

Paul Mees of RMIT has compiled and compared official data on the density of North American and Australian cities. His peer-reviewed work shows that the densest city in the United States is not New York but Los Angeles, which few Australian urbanists aspire to emulate.

Sydney, Australia’s densest city with 20 persons per hectare is only three quarters as dense as Los Angeles, which has 27 persons per hectare. Yet public transport commuting in Sydney is five times the Los Angeles rate. Transport policy, Mees argues convincingly, is at least as important as urban form in shaping a city’s transport outcomes. Density is not destiny.

With high-rise urbanism facing scientific doubts, its advocates often decorate their arguments with circumlocutions about the aesthetic or cultural qualities of high-rise living. These claims are usually subjective and contestable. For every high-rise architectural masterpiece there are dozens of shoddy apartment blocks thrown up with little ecological or aesthetic concern.

The supposed “vibrancy” of high-rise living is often balanced against provision of green open space, especially at the neighborhood scale. Children’s development advances through free physically active play but a recent literature review by my colleagues Jason Byrne and Neil Sipe argues planning for higher densities rarely considers children’s needs. Blubberville anyone?

Why then have views favoring high densities gained traction? Despite the waning of the old cultural cringe, a view persists of Australia’s essential suburban character – where most of us live – as artless against the boulevards of Europe or the boogie-woogie of New York.

The intellectual misadventure of high-rise urbanism also perpetuates a pernicious bias in Australian environmental debates in which less affluent suburban dwellers are treated as environmentally unsophisticated “bogans” – a stereotype recently denounced by Melbourne University’s David Nichols.

It fits within a long and regrettably continuing Australian tradition of denigrating suburbia whose recent version sneers at “aspirationals” in suburban “McMansions” driving “monster-trucks”. That complaints about suburban consumption lack objective scientific foundation, raises suspicions that the anti-suburban prejudice serves to deflect scrutiny from the more harmful consumption patterns of wealthier – and typically denser – inner urban households.

Those who criticise high-rise urbanism, though, risk being cast as apologists for urban sprawl. Disagreeing with Sydney’s Barangaroo proposal, for example, doesn’t equate to support for the latest fringe growth area splurge.

More single, detached dwellings in low-density estates at the suburban fringe also causes harms. These range from the destruction of bio-diverse habitats to the social isolation of new residents from work and services. My own work on household oil vulnerability clearly reveals the future perils from higher fuel prices already planned into the fabric of many of our car-dependent fringe suburban zones.

So how dense should we be? One possibility is a mid-level suburbanism. Focused nodes of three to six storey developments – terraces, walk-ups and low-rise apartments – are dispersed across an entire metropolitan area, not just inner zones. Tied to an employment decentralisation program where more jobs exist outside the CBD, such nodes can then be used to anchor improved suburban public transport networks.

As Paul Mees has shown, suburban densities can easily support high quality public transport if we plan our networks effectively. Such a model can accommodate new residents more widely across the city, and avoids the ecological damage of very high or low densities.

There is an even better solution to the density debate though. Maybe we should abandon our obsession with density as a driving objective of urban policy and instead design our living environments to best accommodate our overall economic, social and environmental goals, at whichever scale is most appropriate.

This means viewing density as just one instrument among many in our urban toolkit. We should use it carefully and selectively, not as a universal prescription that is forced unthinkingly upon our cities.

It similarly requires us to understand the form of our cities as the effect of urban social, economic and institutional processes, not the determinant. People congregate and interact in cities because of social and economic logics, not because they were made to by urban form.

Refreshingly, the draft Australian national urban design guidelines shy away from installing density as a driver of urban outcomes and instead propose methods that could operate at any scale of urban form, albeit rather innocent of the social and economic processes shaping cities and their appearance.

We could be very dense in the way we plan our cities. But we can be much cleverer than that.