More low-down on tall buildings
Growing research paints a decidedly mixed picture on their benefits — with significant implications for responsible best practice.
It’s become a truism among many sustainability advocates that tall buildings are, by sheer virtue of the density they provide, paragons of sustainability. The most recent addition to this canon comes from Harvard economist Edward Glaeser, writing in The Atlantic ("How Skyscrapers Can Save the City"). Some proponents advocate a wholesale move to super-dense “skyscraper cities,” while others simply tout the green credentials of particular tall buildings, like London’s Gherkin or Manhattan’s New York Times Building.
Indeed, the research does show that places like Manhattan and Vancouver, BC, perform well on ecological criteria: They conserve farmland and natural areas, they have relatively low energy use and emissions per person, and they have relatively efficient use of resources per person (in things like buildings, pavement, etc).
But how much of this is due to the presence of tall buildings? How helpful are tall buildings in and of themselves?
More pointedly, does the research show that there actual negatives that we, as responsible practitioners, must bear in mind?
In a word, yes.
There is a growing body of research on the benefits and drawbacks of tall buildings, and this research gives a decidedly mixed picture. Indeed there are significant negative ecological impacts of tall buildings, as well as other negative factors, and the ecological benefits are not as great as is often assumed. We summarize some of this research below, and offer a sampling of citations.
As a recent UK House of Commons report concluded, also summarizing the research (citation below): "The proposition that tall buildings are necessary to prevent suburban sprawl is impossible to sustain. They do not necessarily achieve higher densities than mid or low-rise development and in some cases are a less-efficient use of space than alternatives."
Often cities like New York and Vancouver are cited as stellar examples of dense ecologically superior cities with tall buildings. It’s usually assumed that it’s the tall buildings in these cities that give them the edge. (Indeed, Glaeser himself makes this conflation.)
These cities are indeed very positive when it comes to carbon and other ecological metrics. But it’s often overlooked that tall buildings are only a fraction of all structures in these places, with the bulk of neighborhoods consisting of rowhouses, low-rise apartment buildings, and other much lower structures. They get their low-carbon advantages not from density per se, but from an optimum distribution of daily amenities, walkability and access to transit, and other efficiencies of urban form.
Three common types
Where tall buildings do exist in these cities, they often fall disproportionately into three categories (in large part reflecting economic forces). They are usually either single-use or limited mixed-use office buildings; or they are residential towers inhabited mostly by wealthy families (who frequently have additional homes elsewhere); or they are affordable public housing projects created by government.
Of course, many of the tall buildings that house the poor — in the US, and internationally — have an unhappy history. There is extensive research on their dysfunctions, calling into question their social suitability for families, their impact on children, their psychological impacts, their relation to their open spaces and propensity for crime, and other social issues. Moreover, in most cases these are not simply correctable design defects, but inherent problems stemming from isolation from the ground, lack of eyes on the street, and other attributes of tall buildings.
Office buildings, of course, don’t do anything by themselves to increase residential density, and depend for many of their benefits on their location and the pattern of commuting. If they are confined to largely single-use office districts whose employees empty out in the evening, decamping to remote residential enclaves, then this is clearly not much of an ecological benefit.
Residential towers that segregate by income are also obviously problematic — in effect, forming “vertical gated communities” that limit interaction and social capital across socio-economic groups. Moreover, like horizontal gated communities, they bottle up the activity of residents that might otherwise help to enliven the public realm. Lastly, there is the simple and rather embarrassing fact that when it comes to residential density, you can’t count people more than once: if wealthy tower residents have two or three homes, then their residential population count has to be divided between these. This fact alone reduces the conventional density count of some higher-end residential tower neighborhoods (like those in Vancouver) significantly.
We should certainly acknowledge the advantages and appealing qualities of tall buildings (for example, the views they afford — at least when not blocked by another tall building!). But as the citations below reflect, many common assumptions about the ecological benefits of tall buildings are simply not supported by the evidence.
Often the case for tall buildings is made on the basis of the most obvious beneficial effect for sustainability, that of increased density. But there are two important points here:
Placement as well as density
One, it is not just density, but the efficient placement of people and their activities, that is important. A dense downtown, far away from a dense bedroom community, may actually be worse, from a carbon point of view, than a less dense mix of the two.
Two, research shows that the benefits of density are not linear, but taper off as density increases. In other words, there is an optimum density, above which the negative effects of density start to increase over the positive ones. That "sweet spot" seems to be in the neighborhood of about 50 people per acre. And many cities around the world achieve this density without tall buildings, and while creating a very appealing, livable environment (e.g., Paris and London, as well as the aforementioned parts of New York, Vancouver et al.).
We would not argue that tall buildings are never appropriate. However, an evidence-based approach would caution us to put the burden of proof on the proponents, not the opponents, of tall buildings, to prove their overriding benefits in a given situation.
The research shows that negative effects of tall buildings include:
- Increasingly high embodied energy of steel and concrete per floor area, with increasing height
- Relatively inefficient floorplates due to additional egress requirements
- Less efficient ratios of common walls and ceilings to exposed walls/ceilings (compared to a more low-rise, "boxier" multi-family form — as in, say, central Paris)
- Significantly higher exterior exposure to wind and sun, with higher resulting heat gain/loss
- Challenges of operable windows and ventilation effects above about 30 stories
- Diseconomies of vertical construction systems, resulting in higher cost per usable area (not necessarily offset by other economies — these must be examined carefully)
- Limitations of typical lightweight curtain wall assemblies (there are efforts to address this, but many are unproven)
- Challenge of maintenance and repair (in some cases these require high energy and cost)
- Psychological effects on residents — evidence shows there is reason for concern, especially for families with children
Effects on adjoining properties:
- Ground wind effects
- Shading issues (especially for other buildings)
- Heat island effects — trapping air and heating it, placing increased demand on cooling equipment
- "Canyon effects" — trapping pollutants, reducing air quality at the street
- Social effects — "vertical gated community" syndrome, social exclusion, lack of activation of the street
- Psychological effects for pedestrians and nearby residents. This depends greatly on the aesthetics of the building, but there is research to show that a novel design that falls out of fashion (which history shows is difficult to predict) can significantly degrade the experience of the public realm and quality of place. This in turn has a major effect on sustainability.
The last factor is one of the most controversial among architects, who argue that this implication maligns their profession — notably in the post-war era of Modernism. But the evidence does point to clear failures of Modernist high rise schemes of the post-war period — to the point that many have had to be demolished. This is certainly not a sustainable strategy; and while it hardly proves that all tall buildings will suffer a similar fate, it does argue for a precautionary approach, and one that places an evidentiary burden on the proponents of tall buildings.
After all, these buildings, to a much higher degree, intrude into the daily lives of the surrounding residents. In a democracy, it would certainly seem that those residents ought to have some say as to the buildings' appropriateness. Indeed, as we are arguing, in light of the considerable weight of evidence about the drawbacks, it is the proponents of a given project who must demonstrate that those negatives have been fully mitigated.
A sampling of citation excerpts is below:
I. Energy, Economics and Architecture
I. Guedi Capeluto, Abraham Yezioro, Daniel Gat and Edna Shaviv
Faculty of Architecture and Town Planning
Technion - Israel Institute of Technology
Technion City, Haifa 32000, Israel
Eighth International IBPSA Conference
August 11-14, 2003
"Very often, high rise buildings are proposed as a means of achieving high urban density. However, tall buildings may cause environmental problems like high wind velocities in open spaces around them, as well as extended shadows over nearby houses and open spaces (HELIOS, 1999, 2000). Moreover, the construction cost of high-rise buildings is steep (Tan, 1999, Gat, 1995). When all these factors are taken into account it is not a priori clear that the desired high urban density can be achieved by tall buildings along with an acceptable solution to the above mentioned environmental problems. Recent studies have shown that a reasonable density may be achieved with six stories high buildings while preserving the solar rights of neighboring buildings, as well as open spaces among them (Capeluto and Shaviv, 2001)."
Citations given above:
HELIOS Ltd. (Shaviv, Yezioro and Capeluto). 1999
The Influence of High-Rise Buildings on their Energy
Consumption and Urban Shading (research report in
Hebrew), ordered by the Ministry of the Interior.
Tan W. 1999. Construction Costs and Building
Height, Construction Management and Economics,
Vol. 17, pp. 129-132.
Gat D. 1995. Optimal Development of a Building
Site, Journal of Real Estate Finance and Economics,
Vol. 11, pp. 77-84.
Capeluto I.G., Shaviv E. 2001. On the Use of Solar
Volume for Determining the Urban Fabric, Solar
Energy Journal, Vol. 70, No. 3, Elsevier Science
Ltd., pp. 275-280.
II. An Analysis of the Embodied Energy of Office Buildings by Height
G.J. Treloar, R. Fay, B. Ilozor, P.E.D. Love
Journal: Facilities Year: 2001 Volume: 19 Issue: 5/6 Page: 204 - 214 ISSN: 0263-2772 DOI: 10.1108/02632770110387797 Publisher: MCB UP Ltd
"Aims to compare the energy embodied in office buildings varying in height from a few storeys to over 50 storeys. The energy embodied in substructure, superstructure and finishes elements was investigated for five Melbourne office buildings of the following heights: 3, 7, 15, 42 and 52 storeys. The two high-rise buildings have approximately 60 percent more energy embodied per unit gross floor area (GFA) in their materials than the low-rise buildings. While building height was found to dictate the amount of energy embodied in the "structure group" elements (upper floors, columns, internal walls, external walls and staircases), other elements such as substructure, roof, windows and finishes seemed uninfluenced."
Excerpt from conclusion:
"Alternatives to tall buildings should be sought, but where unavoidable, measures to reduce the size of the building, reduce the intensity of material usage (especially energy intensive and nonrenewable materials) and to minimise wastage should be fully explored."
III. The Consequences of Living in High-Rise Buildings
Department of Psychology and School of Environmental Studies, University of Victoria, Victoria, British Columbia V8S 2H1, Canada
Tel: 1 250 721 7532; Fax: 1 250 721 8929; Email email@example.com
"A full account of architectural science must include empirical findings about the social and psychological influences that buildings have on their occupants. Tall residential buildings can have a myriad of such effects. This review summarizes the results of research on the influences of high-rise buildings on residents' experiences of the building, satisfaction, preferences, social behavior, crime and fear of crime, children, mental health and suicide. Most conclusions are tempered by moderating factors, including residential socioeconomic status, neighborhood quality, parenting, gender, stage of life, indoor density, and the ability to choose a housing form. However, moderators aside, the literature suggests that high-rises are less satisfactory than other housing forms for most people, that they are not optimal for children, that social relations are more impersonal and helping behavior is less than in other housing forms, that crime and fear of crime are greater, and that they may independently account for some suicides."
IV. The Revival of High-rise Living in the UK and Issues of Cost and Revenue in Relation to Height
Kunze, J. (2005) The revival of high-rise living in the UK and issues of cost and revenue in relation to height. Masters thesis, UCL (University College London).
"The following report explores the recent revival of tall residential buildings in the UK as well as issues of costs and revenues for such projects. The first part of the paper focuses on the background and the preconditions of the revival. The history of tall residential buildings and its impact on the image of highrise living is explored as well as some of the debate that surrounds the topic. However, the vast amount of related social, urban design and environmental issues are not part of the analysis. The phenomenon of the revival is described in numbers of completed buildings and with examples of built and proposed projects. Characteristics like the new type of occupiers and the provision of affordable housing are highlighted. The second part of the report and the main part of the research focus on the economic drivers behind tall residential developments. The issues of building costs and sales prices in relation to height are explored and values are gathered in several interviews with professionals. The findings are analysed and applied in a series of model calculations for developments with heights from 5-50 storeys. It seems that the disadvantages of building high are not balanced out by a premium in sales prices for height. The evidence found suggests that the economics of tall residential buildings change dramatically above 20 storeys. This corresponds with the height of structures that were built in recent years. However, the paper concludes that the data available was not sufficient to establish robust quantitative relationships between residential developments of different heights and that it is necessary for the benefit of all that more research on this topic is made publicly available."
V. The Tower: An Anachronism Awaiting Rebirth?
VI. Harvard Design Magazine: "New Skyscrapers in Megacities on a Warming Globe"
Number 26, Spring/Summer 2007
"Is the tall building an anachronism? Does it, like sprawling suburbia and out-of-town shopping malls, seem doomed to belong only to what is increasingly referred to as "the oil interval," that now fading and historically brief moment when easily extracted oil was abundant and cheap? The answer is probably "Yes"....
" ... What kind of city nurtures [today's] very different workforce that is in touch with and wants to live in accord with its deeper values? Ask people how they believe they should really live; the clearer they become about this, the more obvious it is that such a lifestyle is very difficult in the contemporary city. Do we want to live in a city of glistening towers, of spectacle and the restless excitement that fuels and is fuelled by excessive consumption? Or would we prefer a mid-rise city with a more finely grained, more intricately rich and varied urban fabric offering choice, contrast, respite, and surprise - a convivial city where community has a chance of being reestablished? Sustainability requires not only that we lessen our ecological impacts, but also that we create the urban and cultural frameworks in which we can attain full humanity, in contact with self, others, and nature. This might be the real reason that the tower seems an anachronism. There may be a few clusters of green towers here and there, but their presence might be limited in the compact and convivial cities of the future."
VII. The Influence of a Tall Building on Street-Canyon Flow in an Urban Neighborhood.
Bowker, G. E., D. Heist, S. G. Perry, L. Brixey, R. S. Thompson and R. W. Wiener.
U.S. EPA Office of Research and Development, National Exposure Research Lab. Presented at 28th
NATO/CCMS International Technical Meeting, Leipzig, Germany, May, 2006.
VIII. Canyons Up the Pollution Ante
Mead, M. Nathaniel
Environmental Health Perspectives, July 2008; Vol. 116, No. 7, p. A28.
" … a new study focuses on how traffic emissions are dispersed within urban street canyons -- streets that are lined with tall buildings on both sides. Within these domains, large quantities of pollutants are released near the ground from motor vehicle exhaust, then trapped and concentrated within the canyon walls. Urban street canyons also tend to contain a lot of people, potentially making these areas high-risk zones for big cities. … population exposure to traffic pollutants in New York’s urban street canyons can be up to 1,000 times higher than exposure to a similar amount of emissions in other urban settings."
IX. Tall buildings: Report and Proceedings of the House of Commons
Transport, Local Government and the Regions Committee.
Sixteenth report of Session 2001-02.
London, UK Stationery Office, 4
September 2002, HC 482-I
"The main reason that the Committee held an inquiry into tall buildings was to identify the
contribution which they can make to the urban renaissance. We found that contribution to
be very limited. The proposition that tall buildings are necessary to prevent suburban sprawl is impossible to sustain. They do not necessarily achieve higher densities than mid or low-rise development and in some cases are a less-efficient use of space than alternatives. They have, for the most part, the advantages and disadvantages of other high density buildings. They can be energy-efficient, they can be part of mixed-use schemes and they can encourage the use of public transport where there is spare capacity, but so can other types of high density developments. Tall buildings are more often about power, prestige, status and aesthetics than efficient development."