Image Source: Image courtesy of Bon Bahar from Unsplash
As urbanization rates continue to skyrocket around the globe, density has been touted as a solution to reduce urban sprawl and reduce growing urban ecological footprints. From new urbanist online organizing spaces to city planning draft boards, calls for increased urban density have replaced the once idyllic notion of the sprawling, tranquil suburb. Yet it is a myth that density alone is an adequate response to growing urban ecological footprints worldwide. Density can be a practical component of green city planning, but only if it is combined with other planning improvements. We ought to analyze the shortcomings of density as a catch-all solution to urban planning. This will enable us to think critically about how density, when working in concert with other urban planning improvements, can be an effective solution to reduce urban carbon footprints.
One of the most significant environmental drawbacks of density-based urbanism projects is the carbon-intensive construction process. When density is increased in an urban neighbourhood, already existed buildings and spaces are demolished. This creates non-recyclable waste and in the case of some older building materials, environmentally hazardous materials such as asbestos can be released into local ecosystems. However, most of the carbon cost of a project lies not in the method of construction, but rather in the construction materials themselves. In Canada, steel, glass and concrete are the primary construction materials for high-density construction projects. Each material is produced through a carbon-intensive process that includes ecologically devastating resource extraction operations, not to mention the energy and carbon-intensive manufacturing processes. Beyond their environmental costs, steel, glass and concrete also act as natural heat sinks. When used as construction materials, their heat retention dramatically adds to the heating and cooling energy requirements of a building. This is but one example of how the choice of construction material can continue to contribute to an urban carbon footprint, even years after the building itself has been constructed.
Even lower density buildings suffer the same fate as their high-density counterparts. Take for example the classic “5 over 1” model of development, the name signifying a six-story medium density building with five levels of wooden construction over a single ground story built from concrete. These buildings are often lauded as ecologically friendly construction, since renewable materials like wood are used instead of carbon-intensive materials like steel. However, the type of wood used in construction is not entirely renewable, and these buildings also employ other carbon-intensive materials. While wood is a renewable material on its own, wood employed in construction must be weather-treated, a process which involves applying multiple coats of petroleum-based solutions to the wood to protect it from moisture. Further, the pressure-treated wood cannot be exposed directly to the elements and must be shielded by a façade. The materials used to build this façade are usually made from vinyl, which is another petroleum-based product with a carbon-intensive extraction and refining process.
The solution to this first drawback of density is relatively straightforward. Rather than demolishing neighbourhoods to rebuild them with increased density, more efforts should be directed towards the retrofitting of existing buildings. While construction could be made more sustainable through the use of more renewable materials, it is almost always less-carbon intensive to simply retrofit and upgrade an existing building than it is to demolish it and build a new structure. Some legislators have noticed this and have begun to formulate economic incentives for landlords and developers to retrofit and redevelop their properties rather than tear them down. In their 2019 proposal for a provincial Green New Deal, for example, the Ontario New Democrat Party proposed the creation of a provincial subsidy for financing the retrofitting of existing buildings.
However, due to growing populations worldwide and an explosion in urbanization rates, it is not always possible to simply retrofit an existing building and avoid building new construction. In these cases, the use of less carbon-intensive building materials and construction practices is essential to controlling urban ecological footprints. For example, the use of brick and masonry instead of steel and cement could drastically reduce the carbon footprint of new construction. Such materials are not always the most cost-effective when compared to their more carbon-intensive alternatives, but a government subsidy or financial incentive could level the playing field and make less carbon-intensive construction materials a more viable option for developers. The implementation of a mandatory carbon neutrality policy could be an opportunity to encourage more ecologically responsible construction. Under such an approach, developers would have to offset the carbon cost of their new construction projects by building or funding eco-friendly offsets. The city of London is currently considering such a proposal as part of an effort to make the city carbon-neutral by the year 2050.
Another drawback of newly built urban density is the requirement for services to scale as population grows. When a neighbourhood increases in density, it creates a new group of citizens requiring access to services and goods. For individual businesses and commercial enterprises in that neighbourhood, this can be a considerable advantage as they now have access to a greater customer base. However, the larger population can also put more pressure on the delivery of services, particularly if the services were already strained. Transportation is one of the services that is put under the most stress by growing populations. High-density developments are promoted as a solution to urban and suburban sprawl. Rather than have a commuter travel long distances through low-density suburbs, high-density developments allow commuters to travel less distance due to everything being more compact. While this is true in theory, it is not always the case in practice. Without the proper infrastructure, the potential ecological advantages gained from the density project are lost, and high-density developments do not reach their maximum eco-friendly potential. If residents, workers, or visitors must still travel long distances to access services, the resulting traffic congestion can easily undo many of the density project’s ecological advantages.
There are two solutions to solve this other disadvantage of density. First, high-density developments must be supported by and directly integrated into a robust public transportation system. Access to a transportation system is the best way to shrink a city by making previously inaccessible regions or neighbourhoods accessible to a broader segment of the population. The second solution is the use of mixed zoning to create self-sustaining communities. There is of course an argument to be made for the efficiencies of economies of scale. For example, it doesn’t make sense to build a hospital in each neighbourhood of a city if one large central hospital can service multiple neighbourhoods simultaneously. However, for other services such as shopping and employment needs, accessibility within a single community cuts down on transportation requirements for citizens.
There is one caveat to the seemingly idyllic solution of mixed zoning. Due to the nature of housing and rent prices in urban areas as well as the issue of gentrification, it is not always financially feasible for citizens to live in the same neighbourhood as their place of employment. This is particularly the case for urban service-industry jobs, as those employees, typically working for only minimum wage, cannot afford to live in the neighbourhoods they serve. Increasing the affordability of urban living is thus a significant challenge that will need to be overcome if mixed-use development is to reach its true eco-friendly potential.
To conclude, high-density urban developments are not the catch-all solution to reducing urban carbon emissions. This is due to the carbon-intensive nature of construction and the requirement for services to adequately scale with population increase. Instead, when combined with mixed zoning, a robust transportation network and eco-friendly development practices, density can play an integral role in rethinking urban landscapes and making them more eco-friendly.