Unsustainable, in need of reinvention or the perfect answer to economic obsolescence in the city? As part of its Building Futures initiative, the RIBA commissioned three viewpoints on tall buildings
Tall is beautiful
Peter Ferrari
If we look back at the 20th Century to identify some of its most sustainable structures – those which have stood since its early decades and are approaching their centenary – we can readily identify some iconic tall buildings.
The Chrysler Building and Empire State Building (completed in 1930 and 1931 respectively) are early examples of truly tall buildings. From the 1930s onwards these ‘skyscrapers’ have proliferated across the globe – many are still standing.
As a developer active in the industry for over 25 years, I now regularly hear of buildings that were developed at the beginning of my career being demolished and redeveloped.
Typically, this is not, as some might expect, because the buildings are functionally obsolete. In most cases they could easily have been refurbished or converted for another 25 years, or more, of useful life.
It is because they are economically obsolete. Or, to put it another way, the owner can achieve more density on the site through re-development.
It is a simple and inviolable principle of property development that a rational, structurally sound building will rarely be demolished unless a greater density can be achieved by redevelopment. Many of the tall buildings constructed in the 20th Century are here to stay, as they have maximised the density available on their particular sites.
The tall building, with its relatively small footprint and high levels of natural light, is the most flexible of buildings. Suitable for use as offices, hotels and apartments they can be converted to these different uses as economic cycles wax and wane across the property sectors (the Metlife Tower, for example is being converted into a hotel). So, yes, the tall building can be an answer to our increasing population. In the right place, properly designed and built, they aid the efficient long term use of land and infrastructure.
‘Rational, structurally sound building will rarely be demolished, unless a greater density can be achieved on site in the redevelopment’
However, tall is not always good. High density development has to be accompanied by high levels of demand for accommodation, the provision of high quality infrastructure and services. A skyscraper in a desert (actual or metaphoric) is no good to anyone. But good tall buildings in dynamic, growing city centres are a logical, economically viable and sustainable form of development. Land is a finite resource. Serviced land is even rarer and more valuable.
Tall buildings provide excellent living, working or leisure environments. Ask anyone who works or lives in a well designed tall building. Or visit the restaurant at the top of Heron Tower for a truly uplifting experience!
Peter Ferrari is managing director, property, at Heron International
Historically, tall buildings have been seen as a symbol of success and prosperity. But we need to recognise that they do not increase the sustainability of our cities. We are learning to make buildings that consume less energy and have a lower carbon footprint, but we can use these techniques for all building heights. We should compare the best tall buildings with the best of the shorter.
‘The best low carbon cities are not the most dense but those with a good distribution of amenities, which are easy to walk around, and have good access to transport’
It is often argued that there are benefits to a reasonably high density where we can have easy access to everything we need. But these benefits do not increase in line with density, and at densities above about 50 people per acre the negative effects become apparent.
The research of Serge Salat, founder of the Urban Morphology Lab in France, shows that as well as density, the morphologies of the building stock – how our streets are laid out and the relative proportions of the buildings – must be considered in order to get a balanced view of energy and CO2. He studied housing in Paris, and showed that the shape factor, which defines the amount of exposed building envelope per unit volume, and the amount of volume near the perimeter of the building that does not require artificial lighting, are the most significant parameters in determining the amount of energy required. A high shape factor means more energy is consumed. He showed that the comparatively low rise areas of the traditional parts of Paris are more efficient than those with high rise developments. Other studies showed that six to 10 storeys can achieve effective densities.
Density isn’t everything. Commuting from a dense downtown business area to a dense residential area can produce more carbon than a less dense mix of the two. In Paris, business and residential activities often occur side by side, which can be more sustainable. Having tall buildings in the city for the wealthy won’t necessarily increase density, as many of those people have second or third homes.
The best low carbon cities are not the most dense but those with a good distribution of amenities, which are easy to walk around, and have good access to transport.
Density isn’t a valid excuse for tall buildings and this is important because there are many problems with this typology. Tall buildings:
> Use more steel and concrete per square metre of floor space that can be occupied. A huge amount of energy needs to be saved in the running of the building if it is to match the efficiency of a lower one. The taller the building, the less likely it is that we can use low-carbon timber, and the higher the embodied energy per usable square metre.
> Need far more space for vertical circulation, decreasing the ratio of net to gross floor areas.
> Need additional energy-hungry lifts.
> Are more exposed to wind and sun, leading to higher heat gains and losses for the same amount of insulation.
> Cost more per square metre to build.
> Cost more per square metre to maintain and repair.
> Have an adverse effect on the mental health of occupants. This is particularly true in housing, especially for families with children. Crime and fear of crime is also greater in tall buildings.
> Make the city less permeable at street level: as they get taller they also get wider.
The psychological issues are significant and important. Many high buildings have a sad history, with lack of maintenance, a propensity for crime, and isolation from the life and chances for social interaction at street level. Those that segregate residents by income tend to form vertical gated communities, bottling up key activities that might otherwise activate the public realm at ground level. The fact that running and maintenance costs are higher is particularly problematic for those on lower incomes. In this age of cuts it really can’t make sense to saddle cash-strapped councils and the less well-off with buildings that are going to deteriorate if they are not maintained.
Tall buildings make bad neighbours. Wind effects at ground level get worse, and can’t be completely mitigated by canopies. They cast large shadows, taking away sunlight and pleasure, and blocking access to solar power. They produce ‘canyon effects’ where pollutants from motor vehicles are trapped and concentrated at street level, reducing air quality. The population’s exposure to traffic pollutants in New York’s street canyons can be 1000 times higher than they would be to a similar quantity of emissions in other urban settings.
Security remains an issue. Post 9/11 some corporations may not want to be near buildings that are potential targets. Tall buildings also tend to have more services ducts, which makes them a potential breeding ground for mould, particularly in hotter climates, and even vulnerable to biological attack.
We will probably continue to build some tall buildings, but we should concentrate on creating urban and cultural frameworks that allow for good personal interactions, provide places for chance encounters, respect our ageing population, and allow frequent contact with nature. In wealthy societies a rich family with children aspires to a detached house with a garden. They might want a high-rise flat too, but we must focus on the needs of the majority.
We need to concentrate on designing a built environment that provides opportunities for happiness. I see no evidence that tall buildings give us the best chance of achieving this.
We need to balance the needs of the planet, environment and people. We need to achieve maximum efficiency with minimal resources, and at the same time achieve social harmony.
Jane Wernick is a structural engineer and founder of Jane Wernick Associates
Rethinking the skyscraper: A vertical theory of urban design
Ken Yeang
We need to reinvent the tall building typology. In many tall buildings the volume of built up space can exceed several hectares, yet most of these structures today are nothing more than a series of repeated homogenous concrete floors plates stacked one on top of another, often in a single-use building, and only occasionally with multiple uses. It is this homogeneity that gives so much of our high-rise development its bad reputation.
In our rethink, we need to design the tall building as ‘vertical urbanism’. We need to take all those aspects of urban design that are conventionally crucial at the horizontal plane – place making, creating public realm, figure ground relationship, configuring the spaces between buildings, creating communities, providing public and private accessibility systems, establishing desire lines, maintaining ecological nexus in landscaping, creating vistas – need to be reconnected and transposed to the vertical dimension.
Take for example, place making. By thinking of ‘vertical urban design’ we start to consider a new way of designing tall buildings, with a cornucopia of new design opportunities, in a new vertical theory of urban design. There are a number of ways to accommodate urban growth.
The most commonly preferred approach, incurring the lowest capital cost, is to optimise land use within existing city boundaries – to build on brownfield sites within city limits and intensify land use where it can be sustainably justified, such as over existing transport hubs.
This often results in tall buildings. With continued city growth tall buildings will likely be with us for a while, whether due to high land prices, owners’ egotistical desire for height, or by necessity due to rapid urban growth.
We should also look to take the opportunity when possible to retrofit the existing building stock, utilities and landscaping – a co-ordinated move towards an eco city. Moving these concepts to reality requires a change in the design profession’s mindset but does not need new construction and engineering technologies. They already exist, we just need architects and engineers to rethink their application. What is crucial is to use the latest cleantech systems; engineering systems that are low in embodied energy and construction systems that can be disassembled for future reuse and recycling of materials.
For cities that are already densely populated by skyscrapers, where scarcity of land is an issue (such as Singapore or Hong Kong), we should look at alternative ways of adapting existing built forms; by intensifying existing vertical buildings through horizontal links at upper levels, through better use of the ‘spaces between buildings’, through the use of spaces over existing roads and motorways, through better urban design and physical planning and with more efficient internal use of space, etc.
The retrofitting of our huge existing stock of buildings will become an even greater imperative than the design and construction of new tall buildings in the move to make our cities green and sustainable. This does not mean the widespread demolition, rebuilding and regeneration of urban areas but could mean careful retrofitting and insertions.
The challenge in making tall buildings part of the solution for sustainable urban growth, will be in finding efficient and rapid ways to make existing cites green, such as converting their energy systems to renewable energy systems, ensuring closed-cycle water management systems, implementing citywide sustainable urban drainage, providing an ecological nexus linking the city’s green areas with its hinterland’s natural landscape to make the region’s ecology whole, developing a network of localised food production, reduction of urban pollution and reduction of waste by recycling, and so on. There are of course other physical design issues in the new intensive vertical city such as multiple vertical land uses, enabling privacy and engendering habitable communities while ensuring adequate fire and safety issues, and the like.
Planning legislation to enable the new city as a three dimension urban design matrix of multiple spaces and functions is also needed alongside all this.
Ken Yeang is chairman and design director of Llewelyn Davies Yeang.
These pieces are all drawn from the RIBA’s Building Futures’ Think Pieces on tall buildings. For more on the issue and stimulating discussion on the future of the built environment and it impact on society visit www.buildingfutures.org.uk