The Sustainable Housing Challenge
4.3 Neighbourhood and City Scale
4.3.1 Where and How to House a Growing Population
Since 2007, more than 50% of the world’s population has lived in urban regions. The UN predicts that, by 2050, close to 70% of the world’s population will be urban [59]. The growth in urbanization is primarily due to population growth and migration/immigration. However, regions around the world have experienced this growth differently. In North America and Latin America and the Caribbean, more than 80% of the population lives in urban areas. This number is closer to 75% in Europe,
just under 70% in Oceania, 50% in Asia, and just over 40% in Africa.
These urban areas range in size, from tens of thousands to tens of mil- lions. While most of the world is experiencing population growth, there are some regions that are experiencing decline, including Japan, South Korea, Eastern Europe, and parts of Germany.
The pressure from population growth has forced cities to find ways to house their growing populations; for many cities, this means going out (expanding the urban growth boundary through suburbanization and peri-urban developments) or going up (building medium and high-rise apartments). Growing outwards to accommodate an increase number of dwellings is most common in places like USA and Australia. This is largely driven by a need for cheap land to build on, with the perception that it helps with housing affordability, and that building new develop- ments is easier and cheaper than urban infill2 or urban renewal/regenera- tion.3 This has caused a loss in natural environment as areas that were forests or agricultural land are now being consumed for the construction of new housing. This creates issues in relation to food security, biodiver- sity loss, and air quality, among others.
There is also an increase in jurisdictions around the world that have altered the natural environment to reclaim space for construction.
Examples include land reclamation in Singapore to increase the size of the island and accommodate more development, and building over waterways on the Gold Coast (Australia) and over mangrove forests in the Niger Delta (Nigeria) for urban expansion. Reclaiming land can be costly and there are several examples of where it has, or could, cause issues longer term. For example, a significant number of developments on the Gold Coast are now at risk from rising sea levels, and the 2021 apartment collapse in Miami (USA) highlights the safety issues around building in such areas [44].
2 Urban infill refers to the development of vacant or underused parcels of land in otherwise built-up or developed areas.
3 Urban renewal, or regeneration, is where an area of a city is targeted for unlocking under-utilized land and amenity. This may involve the redevelopment of existing buildings and infrastructure or the development of vacant land. It can often involve rezoning land, improving an area’s amenity, and improving wider access.
Unfortunately, the design of urban regions in many parts of the world has largely been done in ways that are not optimized for sustainability.
The challenge is that once our built environments are constructed, there are limitations to what can be done to improve outcomes. This applies to the micro and macro level. For example, the way streets and blocks are developed will determine how a dwelling can engage with principles of sustainable design, quality, and performance. While there are design options that can negate some of those challenges (such as access to a cer- tain amount of sun during winter to reduce heating needs), this can add cost and complexity to housing delivery. At a larger scale, the way we have designed our neighbourhoods also creates lock in. For example, adding public transport in the form of trains or light rail to an already established urban area can be costly and limited to existing space and infrastructure, leading to costly and suboptimal outcomes.
4.3.2 Urban Climate Change
In addition to housing a growing urban population, many cities are fac- ing unique challenges related to climate. It is not only the changes in climate that impact housing performance, but also how climate interacts with city design. Many cities have reduced permeable land surfaces due to increasing building numbers and the associated hard infrastructure like roads and paths. With these features, we are now creating our own microclimates in cities through the urban heat island effect. The urban heat island effect occurs when heat is trapped in our urban environments due to high amounts of heat-retaining structures such as concrete and asphalt relative to the amount of natural cooling features such as plants and open space [60]. Temperature increases of up to 15 °C have been found in urban areas due to this heat island effect [61]. This can be det- rimental to the health and well-being of people living in these areas. In British Columbia (Canada), the 2021 heat dome event caused more than 600 heat related deaths, while the 2022 heat waves in Europe caused over 2000 deaths in Spain and Portugal [62]. Increases in temperature also mean that more energy is required for cooling. In Sydney (Australia), researchers found a 9 °C increase in summer temperatures which resulted in an additional residential energy load of 6.4% [63].
Fortunately, researchers and practitioners have identified and tested various strategies for reducing the urban heat island effect. These strate- gies range from increased vegetation, to the use of green roofs, to improved performance through passive design and insulation [63–65]. However, in their research across 48 states in the USA, Roxon et al. [66] find there are some cold climatic locations where the heat island effect can help improve thermal performance and reduce energy bills. This also translates to posi- tive and negative impacts on mortality, with Lowe [67] finding that the heat island effect can increase heat related deaths by about 1.1 deaths per million people but reduce cold related deaths by about 4.0 deaths per million people. The above research highlights that specific heat island responses are going to depend on a range of factors.
Global climate change also impacts housing performance in urban areas. In many jurisdictions, historical climate data is used within regula- tions and support tools to design and build new housing. This means that new housing is unlikely to perform well in a future climate. However, like with the urban heat island impacts, this can have both positive and nega- tive outcomes [68, 69]. Using future climate data, Wang et al. [70] found a mixed result for new housing performance in Australia with perfor- mance decreasing in some climate zones (e.g., Sydney, Darwin, and Alice Springs) but increasing in others (e.g., Melbourne and Hobart) with changes of up to 350% by 2100. However, even this increase was not consistent; beyond a certain increase in average temperatures, a negative performance would be seen. In other research, Chakraborty et al. [71]
found that, based on likely climate change scenarios, there would be a global increase of cooling energy consumption of 15% for apartments and 37% for detached housing. If climate change is more extreme, this could increase cooling energy consumption by up to 121% for detached housing. In Canada, while energy for cooling in apartments is predicted to increase by about 40% by 2070, energy for heating is likely to decrease by 27% [68] which is similar to results for four USA cities studied by Shen [69].
What the above evidence points to is that we should be building for IPCC’s mid scenarios for a future climate, with an assumed mid-range life of a dwelling. For example, if a dwelling was built in 2020 and expected to last 40 years, it should be built for a 2040 climate. This
climate data should not just include temperature but also changes to other areas of the natural environment (such as sea level rise, flooding, and bush/forest fires), and be used to inform housing design, material and technology selection, construction methods, and use. When urban planners and other residential stakeholders are considering these things, they must consider where we are building and living.