How can compact cities keep house prices under control?

Southwark (left): surprisingly un-dense. Image: Getty.

Islington is the most densely populated are in the United Kingdom – yet wandering around the quiet streets of the north London borough, it is difficult to appreciate just how many people live there. Handsome terraces, elegant squares and a plethora of parks disguise the fact that there are nearly 14,000 people per km2.

By comparison, anyone passing through Southwark, on the other side of the Thames, is immediately aware of the crowds of people who live and work in the area. New glass towers loom over the major roads, while older council housing squat heavily on the back streets. Cars crawl through the famously congested roundabout and the air is heavy with pollution.

Yet Southwark has fewer than 10,000 residents per km2. This means it is significantly less dense than many of its more desirable northern neighbours: Kensington and Chelsea, Hackney, Camden, Tower Hamlets and, of course, Islington.

Measuring the benefits of urban density

Increasing the number of people living and working in an area can generate huge benefits for a city. Productivity rises as people spend less time and money travelling, and can share knowledge and ideas more freely. Businesses can reduce their production costs when they have access to a greater choice of specialised suppliers and workers. And it’s cheaper to provide services such as health care, waste collection and buses when more people can use them.

For the first time, researchers have estimated the monetary value of these benefits to urban residents. Their findings have just been published in the first working paper from the Coalition for Urban Transitions, a network of over twenty organisations committed to enhancing the economic, social and environmental performance of cities.

Drawing on more than 300 academic papers, Demystifying Compact Urban Growth: Evidence from 300 Studies Across the World demonstrates that increasing population density generates significant economic returns. The authors find that a 10 per cent increase in the number of people living and working in an area enhances productivity by approximately £54 per person per year. Better access to jobs is worth another £48, while improved access to services and amenities is valued at £38. Increased population density is also associated with better environmental outcomes, including preservation of green space and greater energy efficiency.

All other things being equal, this suggests that compact cities like Hong Kong, New York and Paris are likely to be richer and more sustainable than sprawling cities such as Houston or Melbourne.

Managing the risks of urban density

A more compact city is not a silver bullet: there are also risks associated with increasing population density. Careful urban planning is required to mitigate these risks, and deliver the potential economic and environmental benefits.

First, a 10 per cent increase in the number of people living and working in an area can lead to more congestion, with an estimated cost of £27 per person a year. Significant investment in public transport, cycling lanes and pedestrian walkways is essential to ensure that people can move around the city without cars.

Second, this increase in density increases housing costs by £186 per person per year. Such growth in house prices might benefit people who own their own homes or rent out property – but it will be a challenge for renters. As low-income households are more likely to rent, there is a risk that compact city policies will exacerbate inequality within cities.

Governments can avoid an increase in housing costs through policies to increase housing supply. A steady flow of new homes coming on to the market can have a downward effect on housing prices, which may outweigh the upward effect caused by increasing population density.


Lessons from London

In the 19th century, the city of London undertook a series of extraordinarily ambitious urban infrastructure projects that continue to shape the city. The world’s first underground railway was opened in 1863; today, the London Underground carries an average five million passengers per day.

In the 1860s, a vast network of sewers and drains were constructed to serve the three million people living in London. These pipes ended the waves of dysentery, typhoid and cholera that devastated the city, and continue to be used by over 8m Londoners. These far-sighted investments enabled people to live and work in close proximity to each other, helping to sustain London’s population and economic growth for over a century.

A walk through London today suggests that the city is now struggling to manage population density. Despite Crossrail, the proliferation of cycling lanes and iconic red buses on every street, many people continue to depend on cars. As a result, London has the worst air pollution in Western Europe. A normal day’s exposure is equivalent to smoking 15 cigarettes.

The problems extend from transport to housing. House prices in Islington have doubled in the last decade, a period when real wages have stagnated. The soaring property prices are the favourite topic of struggling renters or prospective buyers. The city needs to build over 50,000 homes a year to keep up with population growth, while redressing decades of neglect in the existing housing stock.  The failures of London’s housing policy were made all too clear with shocking fire that devastated Grenfell Tower and the lives of its residents.

Thousands of people move to London every year for the economic and social opportunities associated with this extraordinary city. Its dynamism is due in no small part to its high population density. However, the city’s strained transport system and spiralling house prices underscore the importance of strategic government intervention to manage the risks of crowding so many people into such a small area. Large-scale investment in public transport and housing are essential to ensure that compact cities are also liveable and affordable.

Sarah Colenbrander is a researcher with the International Institute for Environment and Development (IIED) and senior economist with the Coalition for Urban Transitions. The working paper, Demystifying Compact Urban Growth: Evidence from 300 Studies Across the World, was prepared for the Coalition for Urban Transitions by the Organisation for Economic Cooperation and Development (OECD).

 
 
 
 

Green roofs improve cities – so why don’t all buildings have them?

The green roof at the Kennedy Centre, Washington DC. Image: Getty.

Rooftops covered with grass, vegetable gardens and lush foliage are now a common sight in many cities around the world. More and more private companies and city authorities are investing in green roofs, drawn to their wide-ranging benefits which include savings on energy costs, mitigating the risk from floods, creating habitats for urban wildlife, tackling air pollution and urban heat and even producing food.

A recent report in the UK suggested that the green roof market there is expanding at a rate of 17 per cent each year. The world’s largest rooftop farm will open in Paris in 2020, superseding similar schemes in New York City and Chicago. Stuttgart, in Germany, is thought of as “the green roof capital of Europe”, while Singapore is even installing green roofs on buses.

These increasingly radical urban designs can help cities adapt to the monumental challenges they face, such as access to resources and a lack of green space due to development. But buy-in from city authorities, businesses and other institutions is crucial to ensuring their success – as is research investigating different options to suit the variety of rooftop spaces found in cities.

A growing trend

The UK is relatively new to developing green roofs, and governments and institutions are playing a major role in spreading the practice. London is home to much of the UK’s green roof market, mainly due to forward-thinking policies such as the 2008 London Plan, which paved the way to more than double the area of green roofs in the capital.

Although London has led the way, there are now “living labs” at the Universities of Sheffield and Salford which are helping to establish the precedent elsewhere. The IGNITION project – led by the Greater Manchester Combined Authority – involves the development of a living lab at the University of Salford, with the aim of uncovering ways to convince developers and investors to adopt green roofs.

Ongoing research is showcasing how green roofs can integrate with living walls and sustainable drainage systems on the ground, such as street trees, to better manage water and make the built environment more sustainable.

Research is also demonstrating the social value of green roofs. Doctors are increasingly prescribing time spent gardening outdoors for patients dealiong with anxiety and depression. And research has found that access to even the most basic green spaces can provide a better quality of life for dementia sufferers and help prevent obesity.

An edible roof at Fenway Park, stadium of the Boston Red Sox. Image: Michael Hardman/author provided.

In North America, green roofs have become mainstream, with a wide array of expansive, accessible and food-producing roofs installed in buildings. Again, city leaders and authorities have helped push the movement forward – only recently, San Francisco created a policy requiring new buildings to have green roofs. Toronto has policies dating from the 1990s, encouraging the development of urban farms on rooftops.

These countries also benefit from having newer buildings, which make it easier to install green roofs. Being able to store and distribute water right across the rooftop is crucial to maintaining the plants on any green roof – especially on “edible roofs” which farm fruit and vegetables. And it’s much easier to create this capacity in newer buildings, which can typically hold greater weight, than retro-fit old ones. Having a stronger roof also makes it easier to grow a greater variety of plants, since the soil can be deeper.


The new normal?

For green roofs to become the norm for new developments, there needs to be buy-in from public authorities and private actors. Those responsible for maintaining buildings may have to acquire new skills, such as landscaping, and in some cases volunteers may be needed to help out. Other considerations include installing drainage paths, meeting health and safety requirements and perhaps allowing access for the public, as well as planning restrictions and disruption from regular ativities in and around the buildings during installation.

To convince investors and developers that installing green roofs is worthwhile, economic arguments are still the most important. The term “natural capital” has been developed to explain the economic value of nature; for example, measuring the money saved by installing natural solutions to protect against flood damage, adapt to climate change or help people lead healthier and happier lives.

As the expertise about green roofs grows, official standards have been developed to ensure that they are designed, built and maintained properly, and function well. Improvements in the science and technology underpinning green roof development have also led to new variations on the concept.

For example, “blue roofs” increase the capacity of buildings to hold water over longer periods of time, rather than drain away quickly – crucial in times of heavier rainfall. There are also combinations of green roofs with solar panels, and “brown roofs” which are wilder in nature and maximise biodiversity.

If the trend continues, it could create new jobs and a more vibrant and sustainable local food economy – alongside many other benefits. There are still barriers to overcome, but the evidence so far indicates that green roofs have the potential to transform cities and help them function sustainably long into the future. The success stories need to be studied and replicated elsewhere, to make green, blue, brown and food-producing roofs the norm in cities around the world.

Michael Hardman, Senior Lecturer in Urban Geography, University of Salford and Nick Davies, Research Fellow, University of Salford.

This article is republished from The Conversation under a Creative Commons license. Read the original article.