More than half the planet's population lives in cities, and this figure is predicted to rise to more than 70% by the second half of the century. During the same period, human population will have increased by two billion.
As people have tended to move from rural to urban areas, and the boundaries of those urban areas have been constrained by policies such as the protection of the green belt, so those areas have become more densely occupied, with buildings expanding upwards and downwards, green areas and brownfield sites being developed and homes becoming more compact and closer together.
British architect Richard Rogers, points out that in England, in 1800, just 10% of the population lived in towns and cities, now the figure is 90%, and our population is projected to increase to 62 million by 2035. He suggests it is short sighted to imagine we can sustain anything other than compact lifestyles. See Compact sustainable city for more information.
There are number of methods by which urban density can be measured, including:
- Floor area ratio: Total building floor area divided by the area of the land buildings are built on.
- Residential density: Number of dwelling units in a given area.
- Population density: Number of people in a given area.
- Employment density: Number of jobs in a given area.
Advocates of densification argue that the denser a city, the more sustainable it is, since dense cities use less energy per person than suburban or rural areas where people are spread over a wider distance and so travel more often and further. It is also argued that less waste is produced by dense cities as smaller spaces take less energy to heat and cool and use fewer resources to fit out. In addition, the level of infrastructure and supply chain coordination can be more efficient in areas of high density.
Policies that encourage densification generally also provide for the protection of communities and green and public spaces. Home to over 13 million people, Tokyo is often used as an example of positive densification with a small proportion of high rise construction; an answer to critics who believe that densification necessarily leads to an increase in the number of tower blocks. Advocates suggest the aim should be better organisation and finding ways to increase shared space.
High-density living can be extremely desirable, as the New Town in Edinburgh and Kensington in London demonstrate. Both have at least 250 dwellings per hectare, and yet are extremely expensive and highly sought after. In our most attractive villages and market towns it is the older houses clustered at higher densities in the centre that achieve the highest prices. Building at 50 homes to the hectare and above has created the attractive spaces we like best. At below 50 homes per hectare, it is hard to keep shops, buses, doctors, nurseries and schools within walking distance. The less dense our cities are, the further they sprawl, the worse the traffic problems are.
Traditional southern European towns and villages can have double, triple or even quadruple the density of a typical English town. Continental cities are also built at a much higher density.
Despite this, in 2010, the government’s Planning Policy Statement 3 (PPS3) was revised to remove the national indicative minimum density of 30 dwellings per hectare to give local authorities the '…flexibility to set density ranges that suit the local needs' a position that was re-stated in the National Planning Policy Framework (NPPF) in 2012.
Critics suggest that densification means reducing the private space of inhabitants and point to the fact that, whilst around 50% of the global population lives in cities, they account for more than 75% of the consumption of non-renewable resources, and create around three quarters of global pollution. They also point to the fact that since 1900 our cities have actually become less dense and more extensive.
The successful development of urban areas requires consideration of more than just density and planning policy, rather it needs integrated consideration of; governance and growth, urban development and infrastructure, environment and natural resources, and society and community. See Smart cities for more information.
A Savills Research Report to the Cabinet Office, Completing London’s Streets, How the regeneration and intensification of housing estates could increase London’s supply of homes and benefit residents, published on 7 January 2016, compared two methods of redeveloping social housing estates in London; replacing the existing site with new blocks and towers in a similar layout but higher density (contemporary regeneration) or reintegrating the estates into the surrounding urban fabric (complete streets). They found that the complete streets approach creates greater opportunities for mixed use development and integration into the wider city, resulting in better life chances. Publication of the report coincided with a pledge by David Cameron to tackle social deprivation and poverty by transforming ‘sink estates’ around the country. See Sink estate regeneration plans.
In September 2016, Centre for London published a report suggesting that densification of large estates across in London could allow the construction of between 80,000 and 160,000 homes in the next 20 years.
 Related articles on Designing Buildings Wiki
- A new capital for the UK.
- Built environment.
- Designing smart cities.
- Edge Debate 71 - Can decentralisation solve the housing crisis?
- Floor area ratio.
- Fourth annual planning survey.
- Garden cities.
- Mixed use development.
- Must cities grow to compete?
- Public space.
- Redefining density, making the best use of London’s land to build more and better homes.
- Smart cities.
- Tallest buildings in the world.
- The compact sustainable city.
- The future of the green belt.
- Top 10 skyscrapers located in the UAE.
- Urban decay.
- Urban design.
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