Good and Bad Urban Density
Urban Crossroads #91

The city of Shibam in Yemen is a striking example of a high-density traditional urban settlement. (Courtesy of the Aga Khan Award for Architecture)

The city of Shibam in Yemen is a striking example of a high-density traditional urban settlement. (Courtesy of the Aga Khan Award for Architecture)

City officials and urban planners all over the world are promoting intensification as a primary tool for addressing various challenges facing cities, whether traffic congestion, increased pollution, excessive energy consumption, or urban sprawl.

The idea of intensification is a simple one. It accommodates urban population growth through increasing densities in already developed urban districts, thus boosting the number of people, jobs, and services in a given area, while greatly restricting - if not totally halting - the city’s horizontal geographic expansion.

This is achieved through various interventions such as minimizing - and in some cases eliminating - building setbacks, therefore bringing buildings more closely together, and, most importantly, increasing building height limits.

Intensification offers numerous advantages. It protects agricultural land and forests surrounding cities, which have been decimated at alarming rates throughout the world over the past few decades. It allows city residents to live in proximity to the services and amenities they need - whether places of work, shopping areas, schools, or centers of leisure and recreation, and ideally within walking distance to them. It also provides for a more efficient use of various infrastructure services. Accordingly, public transportation, water and sewage lines, garbage collection, electricity grids, to name a few, all would need to cover smaller urban areas. Although intensification will increase the load on existing infrastructure networks, it remains far more efficient and cost-effective to serve a large number of people in a relatively small area than to serve a relatively small number of people in a large area.

As city residents are more easily able to reach their daily destinations by walking or using public transportation instead of depending on the private automobile, there will be fewer motor vehicles on the road, thus less traffic congestion and less air pollution. Such environmental benefits of intensification don’t end with reduced vehicle emissions, but also include overall urban energy consumption. Infrastructure services that cover smaller areas of the city need less energy to operate. Even energy efficiency on the level of the individual dwelling will be positively affected. Intensification, among other things, translates into a predominance of apartment buildings and attached houses over detached single family homes. The contiguity of these dwellings means they will help heat each other during the winter and cool each other during the summer. While a free-standing house is fully exposed to the elements, the units of an apartment building or a row-housing development help shield each other from the hot summer sun and the cold winter temperatures, and much of the heat coming out of one dwelling will not be lost, but will heat the one next to it or above it.

Intensification in many ways provides a return to pre-modern concepts of urbanism. Human settlements then were far more compact. Sprawling cities were not practical as distances were crossed on foot or using pack animals. Preserving agricultural land surrounding the city also was extremely important as this provided city residents with a level of food security. In hot, arid climates, closely located buildings shade each other as well as adjacent streets, thus taking on a very important climatic role. In this context, the historical cities of the Middle East provide very good models of high urban density. A striking example is Shibam in Yemen, known for its densely-arranged multistory buildings. These tall buildings not only create dramatic visual compositions, but also provide much needed shade, and since they take up a much smaller footprint than shorter buildings covering the same built-up area, they help preserve valuable surrounding agricultural land.

The compactness of the pre-modern city was compromised by the widespread use of the automobile. The automobile allowed people to cross long distances easily and quickly, thus providing city residents with the freedom to live well outside existing city boundaries. Many of those who could afford owning an automobile welcomed the opportunity to relocate away from city centers in more spacious homes with larger gardens, enjoying more privacy, open space, and proximity to nature than what is available within the city. This, however, eventually brought about an incredible and seemingly never-ending expansion of cities that has devoured surrounding areas and has resulted in congested highways, long commutes, and the brutal destruction of agricultural land and forests. In addition, providing such widespread suburban areas with the necessary infrastructure services is very costly and unsustainable. All this makes a strong case for intensification.

Intensification, however, is not without its challenges. Unless it is carefully worked out, it can backfire and cause more harm than good. If not thoughtfully planned and implemented, intensification efforts can easily bring about a rash of high-rise buildings randomly popping up in the city, destroying unities of urban scale in preexisting mature neighborhoods, and resulting in a chaotic mix of building sizes that wreak havoc on urban life. A common manifestation of this phenomenon is the example of high-rise buildings overlooking adjacent single-family houses. In the case of traditional districts, allowing higher levels of densities, particularly through increased building heights, may end up erasing complete areas that had preserved collective memory and heritage.

Moreover, there is only so much in terms of density and building height that a given city district can handle, depending on the size of its streets and the availability of infrastructure services in it. Such limits should not be exceeded unless it is possible to unobtrusively increase the capacity of existing infrastructure networks. Also, intensification is totally meaningless if it does not include zoning regulations that allow and encourage a healthy mix of uses in a given area, including residential, office, and commercial. This would make it possible for people to live and work in the same district and to easily access their various destinations from their homes, on foot or by public transportation, and without the need for the private automobile. In fact, this is why density statistics need to include two sets of information: the number of dwellings or residents in a given area and the number of jobs in that area. A healthy urban district will have high numbers for both. It also should be kept in mind that increased densities require the availability of adequate open public spaces that function as green lungs in the city since intensification will inevitably limit the availability of private green spaces.

All these issues need to be addressed. If not, intensification will bring about the destruction of heritage areas, result in ruptures in the continuous evolution of urban districts, and create conditions of unbearable overcrowding.

As for optimal urban densities brought about by intensification, they are determined by factors such as the capacity of existing infrastructure services in a given area, its urban heritage, as well as prevailing social norms relating to physical proximity. It also should be kept in mind that optimal urban densities will differ from one city to the other. They also will differ from one part of the city to the other. In fact, density statistics are far more meaningful when referring to city districts than to complete cities. Among other things, density statistics for complete cities often will include large underdeveloped and sparsely occupied sections of the city, thus providing for misleadingly low numbers.

Density statistics can be misleading and confusing for other reasons. For one thing, there are different ways of calculating urban density. For example, what is referred to as gross density includes public and private, built and un-built areas, including streets, parks, and other open spaces, while what is referred to as net density only includes built areas and privately-owned open spaces, thus providing higher numbers than gross density. Also, some density statistics provide the number of dwellings in a given area, while others provide the number of residents in that area. In addition, and as mentioned above, none of these numbers are complete without including a count of jobs in that area. Judging from the various numbers that one comes across, it may be concluded that a gross density of about 100 residents and jobs per 1,000 square meters of land is a healthy level to aim for in central city districts.

Beyond issues relating to physical factors, intensification has very strong financial ramifications. Any zoning regulation affecting a given area will influence the price of land in it. Intensification involves protecting agricultural land, thus maintaining a healthy supply of it, stabilizing its prices, and making it unlikely that these prices will undergo any significant rise. In contrast, intensification limits the supply of urban land and allows that land to accommodate higher densities, thus resulting in spectacular increases in its price.

This will cause considerable tensions and resentments as owners of urban land will benefit from windfall profits while owners of agricultural land will see the price of their land stagnate. There of course are ways for addressing such price discrepancies. For example, tax reliefs may be given to owners of agricultural land, while a special “development” tax based on allowed densities would be placed on owners of urban land once they sell or develop that land.

All in all, intensification provides for a very sensible solution for dealing with current urban challenges. The contemporary automobile-dominated city, with its large distances, excessive energy consumption, and destruction of agricultural land and forests - to name a few - is proving to be socially, economically, and environmentally unsustainable. Encouraging the development of more tightly-knit urban fabrics where people are closer to the services and amenities they need, and that are served by decent public transportation systems and public spaces will greatly enhance the quality of urban life for people everywhere.

Mohammad al-Asad

April 02, 2009