The first questions to be asked are: what is a tall building and is there a theory for the design of the tall building? But an even more niggling question is, can there be architectural theory at all? For architectural theory can be perceived as an admirable endeavour to make architecture theoretical rather than a body of theory that is architectural (cf M Linder, 'Architectural Theory is No Discipline', in J Whiteman, J Kipnis, R Burdett (eds), Strategies in Architectural Thinking, MIT Press, 1992).
Being theoretical involves the architect borrowing the techniques and disciplines of the scientist or the philosopher. While this may be grand in describing a particular architect's oeuvre, or beneficial in propping up an architect's work or approach to design, it ignores the fact that architecture does not share many features with philosophy or science.
The practice of architecture
In practice, architectural design is a craft, and a variable one at that. Post modernism has successfully shown up the volatile nature of this craft by its unrestrained use of architectural symbolisms, its frivolous multiplication of the surface area of the built envelope, its prodigious use of unnecessary building materials, its indifference to engineering economy, its extravagant use of land, and its irrational subservience to whim and history instead of the allocation and restriction of excessive consumption of energy resources.
The energy equation
Looking at the global economy today, one has to be increasingly aware of energy as a scarce resource; the need for architects to design for a sustainable future becomes a self-evident imperative. Here lies a likely trump card for affirming theoretical respectability: the design of energy-efficient enclosures has the potential to transform architectural design from being an uncertain, apparently whimsical craft, into a confident science. The theory for the design of the tall building might then be one that derives from energy conservation.
The energy equation
However, this energy equation in design is only part of a greater gestalt in environmental design. Regarded independently, there are essentially three routes to low energy consumption in architecture: through material and component selection; through supplier economics (i.e. a life-cycle approach from 'source' to 'sink'); or through basic design. It is the last route that provides the starting bases for much of the design work here and for the explanation of the buildings' configurations.
The energy equation
My earlier research work (at the University of Cambridge, 1971-1975) had been on the formulation of an environmentally comprehensive framework for looking at the built environment and its relations to the natural systems of the biosphere. A simple partitioned matrix was used to provide a compact structure for describing the sets of inter-relationships and inter-actions that a built system has with its environment (cf F E Emery and E C Trist, 'The Causal Textures of Organisational Elements', in F E Emery (ed), Systems Thinking, Penguin Books, 1969). This matrix also reveals some new meanings in these relationships that can be helpful for design.
Environmentally responsive design
Our current research and development work on the bioclimatic approach is essentially a sub-set of broader environmentally responsive design strategies. We find that there are basically two justifications for the bioclimatic approach, one a comfort-based rationale and the other a passive, low-energy one. The latter eventually was found to be expeditious for us in explaining our environmentally responsive design agenda to commercially minded clients. Energy savings could be easily accounted for in terms of monetary savings.
Absence of design criteria
Although bioclimatic principles are relatively well advanced for low- and medium-rise buildings, there has yet to be adequate attention and research directed at tall buildings. Justifications for greater attention are obvious. Traditional building types cannot suffice as design models for the high-rise since the scale and bulk of the high-rise far exceed any precedent. The tall building being largely a novel (i.e. non-traditional) building type, with new servicing systems, it requires its own set of design premises even though the fundamental principles of designing with climate remain unchanged.
Absence of design criteria
Historically, tall buildings were structures that symbolised religious or imperial power. However, in contemporary times the high-rise, while continuing to exhibit physical dominance, has replaced this religious or imperially expressive role with that of the commercial commodity. We might compare the high-rise building to the Boeing 747 in that, like the airplane, it has become an international piece of technology which every national economy possesses. Even some of the poorest countries in the world have their own fleet of 747s and a number of high-rises in their urban areas. The question then becomes: how do we personalise and make use of this international machinery in a way that enables it to be related to its geographical context?
It might be argued that attention should be given to the wider contextual aspects of bioclimatic urban design or planning. However, most countries do not have the financial capacity to prepare a tabula rasa and start anew with relocated urban centres of low- or medium-rise buildings. Furthermore, if the present urban centres were to be replaced, discarding existing extensive infrastructure investment would be wasteful of resources.
Besides this, the pressures of increased land values. urban accessibility, expanding urban populations, globalisation of commerce and the locational preferences of businesses make tall buildings inevitable. What should be of concern therefore is the way these are designed and whether there are effective planning controls on their location, urban design and built-form height.
The tall building typology
The skyscraper is essentially a multi-storey building generally constructed using a structural frame, provided with high-speed elevators and combining extraordinary height with ordinary room spaces such as would be found in low buildings.
Geometrically, the skyscraper can be regarded primarily as an intensification of built space over a small site area (or over a small built footprint). The tall building type permits more useable floor-space to go higher, to make more cash from the land, put more goods, more people and more rents in one place. The high-rise might be seen as a wealth-creating mechanism operating in an urban economy: it derives from high land values and these are related to urban accessibility, which is in turn a product of road and rail services. The environmental justification is that the high-rise's concentration of commercial activities in an urbanised location enables the reduction of energy consumption in transportation.
The tall building typology
The tall building is also the culmination of a number of building inventions: the structural frame and wind bracing; new methods of making foundations; high-speed elevators; air-conditioning; flush toilets; large pieces of glazing and window framing; advanced electronics and telecommunications; sophisticated indoor lighting; ventilation and cleaning technologies.
The economics of skyscrapers
In aggregate, skyscrapers are creations that result from the optimisation of land costs and building economics, the locational preferences of their occupants, the desire for flagship status of their owners induced by the assertive image associated with the high-rise, and ingenious feats and inventions of architectural and engineering design. However, in optimising the land-area use, tall buildings seek to have the maximum internal area on each floor (net areas) and the maximum gross building area for the site (i.e. maximum plot ratios and minimum net-to-gross ratios).
The economics of skyscrapers
In order to achieve these economic objectives, the following criteria became critical:
• minimum external wall thickness
• minimum vertical support size
• minimum horizontal support thickness
• minimum vertical circulation/service core area
• minimum floor-to-floor height.
The cost justifications for these are obvious. Minimum external wall thickness, reduced vertical support sizes (i.e. column sizes) and efficient core areas increase the net useable (rentable or saleable) floor areas per typical floor. The minimum horizontal support thickness and floor-to-floor heights lower structural costs and the area of external cladding and hence construction costs.
The economics of skyscrapers
These are optimising criteria for design based on efficiency and economy. They do not provide any theoretical construct for design. These criteria, if taken to their conclusion (whether in the case of the low-rise or the high-rise building), will lead to instances where building economics are given precedence over the aesthetic, human or poetic aspects of architectural design. In this case, the built form that results inevitably ends up as a diagrammatic, bland, inarticulate and geometrically efficient box. If there is to be a theory of tall building design, it has to extend beyond building economics.
The bioclimatic rationale
What is the justification for designing with climate? Designing the tall building to take advantage of the meteorological data of the location inevitably means some physical and economic departure from the criteria outlined above. For instance, sun shading increases the thickness of the external wall; external lift cores may be less efficient than a central-core layout. What justification might we have for this departure, besides, of course, reasons of architectural aesthetics?
The bioclimatic rationale
The most obvious justification must be the lowering of costs as a result of decreasing energy consumption in the operation of the building. This can be by as much as 40 per cent of the overall life-cycle energy costs of the building since the bulk of energy consumption happens during its operational phase. Significant savings in operational costs would justify incorporation of climatically responsive design features despite higher initial capital construction costs.
Users of tall buildings
Another rationale derives from the impact on the users of tall buildings. The climatically responsive tall building can enhance its users' sense of well-being while enabling them to be aware of and to experience the external climate of the place. Research in the UK and Japan has shown that more than 40 per cent of users of tall buildings would like the option of being able to open windows to the outside. A climatically responsive design should provide the building's users with the opportunity to experience the external environment (and diurnal and seasonal changes) and, in doing so, to avert the blandness of spending their working hours over a significant part of the day in an otherwise artificial environment that remains constant throughout the year.
A further justification is ecological. Designing with climate would result in a reduction of the overall energy consumption of the building by the use of passive (non-mechanical) structural devices. Savings in operational costs derive from less use of electrical energy which is usually derived from the burning of non-renewable fossil fuels. The lowering of energy consumption would further reduce overall emission of waste heat, thereby cutting the overall heat-island effect on the locality.
There is a further justification - a regionalist one. Climate, viewed in the overall perspective of human history and built settlements, is the single most constant factor in our landscape, apart from its basic geological structure. While socio-economic and political conditions may change almost unrecognisably over a period of, say, one hundred years, as may visual taste and aesthetic sensibility, climate remains more or less unchanged in its cyclical course. History shows us that, with accumulated human experience and imagination, the architecture of the shelter evolved into diverse solutions to meet the challenges of widely varying climates, indicating that the ancients recognised regional climatic adaptation as an essential principle of architecture. In this regard, the climatically responsive building can be seen as having a closer fit with its geographical context.
Our future agenda will obviously involve more on-going research, design and development work into other bioclimatic aspects as well as other ecological influences on building design: the beneficial use of wind and rain; the life-cycle approach to the use of materials and building equipment; and the development of new patterns of internal life for the users of tall buildings. The last involves seeking new patterns of spatial configurations that depart from providing building users with an environment that is simply a concrete tray in the air.
Application in desain
Service core position is of central importance in the design of the tall building. The service core not only has structural ramifications, it also affects the thermal performance of the building and its views, and it determines which parts of the peripheral walls will become openings and which parts will comprise external walls. Core positions can be classified into three types: central core, double core and single-sided core. In the tropics, cores should preferably be located on the hot east and west sides of the building. A double core has many benefits. With both cores on the hot sides, they provide buffer zones, insulating internal spaces. Studies have shown that minimum air-conditioning loads result from using the double-core configuration in which the window openings run north and south, and the cores are placed on the east and west sides. The same considerations apply in temperate zones.
Lift lobbies, stairways and toilets should be given natural ventilation and a view out where possible. Inevitably, this means that they should be on the periphery of the useable floor space. External periphery placement of these parts of the building results in energy savings since they will not require mechanical ventilation and they demand reduced artificial lighting, as well as eliminating the need for additional mechanical pressurisation ducts for fire protection. Aesthetically, by placing these service zones on the periphery, they receive sunlight and have views out which are not possible with a central-core position. The user of the building leaving an elevator at an upper floor can see out and be aware of the place, instead of entering an artificially lit lobby that could be anywhere in the world.
Tall buildings are exposed to the full impact of external temperatures and radiant heat. Accordingly, the overall building orientation has an important bearing on energy conservation. In general, arranging the building with its main and broader openings facing north and south gives the greatest advantages in reducing insolation (and the resulting air-conditioning load).
It frequently happens that the geometry of the site does not coincide with sunpath geometry. In these cases, the other built elements may, if expedient for planning purposes, follow the site geometry (for example, to optimise basement car-parking layouts). Typical floor window openings should generally face the direction of least insolation (north and south in the tropics). Corner-shading adjustments or shaping may need to be done for sites further north or south of the tropics or for non conformity of the building plan to the solar path.
Generally, window openings should orientate north and south unless important views require other orientations. If required for aesthetic reasons, curtain walling may be used on non solar-facing facades. On other faces of the building some form of solar shading is required, while the quality of light entering spaces should also be considered. In temperate zones, transitional spaces can have adjustable glazing at the other face so that balconies or recesses can act as 'sun spaces', collecting solar heat, like a greenhouse or conservatory.
Deep recesses may provide shade on the building's hot sides. A window can be totally recessed to form a balcony or a small skycourt that can serve a number of functions besides shading. Placing balconies on hot elevations permits glazing to these areas to be full-height clear panels. These can give access to the balcony spaces which can serve as evacuation spaces, as large terraces for planting and landscaping, and as flexible zones for the addition of future facilities.
Large multi-storey transitional spaces might be introduced in the central and peripheral parts of the building as air spaces and atriums. These serve as 'in-between' zones located between the interior and the exterior. They should function like the verandahways of the old shop houses or the porches of early nineteenth-century masonry houses of the tropics. Atriums should not be totally enclosed but should be placed in this in-between space. Their tops could be shielded by a louvered roof to encourage wind-flow through the inner arcas of the building. These may also be designed to function as wind scoops to control natural ventilation to the inner parts of the building.
External walls should be regarded as permeable, environmentally interactive membranes with adjustable openings (rather than as a sealed skin). In temperate climates the external wall has to serve very cold winters and hot summers. In this case, the external wall should be filter-like, with variable parts that provide good insulation but are openable in warm periods. In the tropics the external wall should have moveable parts that control and enable good cross-ventilation for internal comfort, provide solar protection, regulate wind-driven rain, besides facilitating rapid discharge of heavy rainfall.
The building plan, in addition to responding to the commercial intentions of the building (for example. enabling single, double or multiple tenancies), should reflect the patterns of life and culture of the place, and its climate. In part this involves an understanding of the spatial modalities of the people, the way they work, the way culture arranges privacy and community. This can be reflected, for example, in the plan configuration, the building's depth, the position and layout of entrances and exits, the means of movement through and between spaces, the orientation and views as interpreted in the plan. The plan should also reflect air movement through the spaces and the provision of sunlight into the building.
Work spaces, even in a high-rise commercial development, have to have some degree of humanity, some degree of interest and some use of scale. For example, large skycourts and terraces might function as communal spaces as well as means of ventilation for the upper parts of the building
Relationship to the street
The ground floor in the tropics should preferably be open to the outside and naturally ventilated. The relationship of the ground floor to the street is also important. The introduction of the indoor atrium at the ground floor may mean the demise of street life. Freestanding fortress-like buildings also tend to separate the building from the pavement, further alienating the street.
Free-standing buildings become isolated on their plots.
Planting and landscaping should be used not only for their ecological and aesthetic benefits, but also to cool buildings. Planting should be introduced as vertical landscaping to faces and inner courts of upper parts of tall buildings. Plants absorb carbon dioxide and generate oxygen, benefiting the building and its surroundings.
Solar shading is essential for all glazed walls facing the sun (generally east and west in the tropics). A number of configurations of passive devices can be used (fins, spandrels, egg-crates, etc.), depending on facade orientation. Shading blocks insolation in summer and prevents heat penetration of the building all year round in the tropics and in summer in temperate zones.
Cross ventilation should be used (even in air-conditioned spaces, to cope with system breakdowns), letting fresh air in and exhausting hot room air. Good air movement promotes heat emission from the human body surface and gives a feeling of comfort. Skycourts, balconies, and atriums as open spaces and transitional spaces at the upper parts of the tall building encourage wind flow into internal spaces. Side vents operating as wind scoops located at the edges of the facade capture wind and make the best use of the high wind speeds found at upper levels. Wind can be channelled into ceiling plenums to ventilate inner spaces.
Insulation and heat stores
Good thermal insulation of the building skin reduces heat transfer, both from solar gain and loss of coolness from the inside. A second skin (a rain wall) can be built over the inner wall with an air gap in between.
Structural building mass may be used to store heat. The mass loses heat during the night and keeps internal spaces cool during the day. In temperate climates, structural and building mass can absorb solar heat during the day and release it at night.
A water-spray system on hot facades promotes evaporation and therefore cooling. In temperate climates, solar windows or a solar-collector wall can be located on the outer face of the building to collect the sun's heat.