High-Rise Buildings: Energy and Density

SUMMARY

The project will seek to answer two questions:

1 Are high-rise buildings more energy-intensive - all other things being equal - than equivalent low-rise buildings?
2 Is it possible to provide the same floor area on the same sites as high-rise buildings, but on much-reduced numbers of storeys?

If the answer to both these questions is yes, then energy could be saved by discouraging tall buildings and encouraging low-rise.

The popular belief is that tall buildings are justified and unavoidable where land is in short supply. However research on density and building form carried out since the 1960s has shown that this belief is open to serious question. Of course if a building occupies the whole of its site, then the only way that floor area can be increased is by adding more storeys. But buildings, as they are made taller, need to be set further apart in order to preserve standards of daylight, privacy and natural ventilation. And buildings with different geometrical forms make use of land in different ways. Speaking very broadly, the same densities achieved by freestanding towers of a given height can be achieved in lower buildings in the form of elongated slabs or terraces, or in even lower buildings in the form of enclosed courtyards.

Meanwhile some scattered research has been done on the use of energy per square metre of floor area in high-rise buildings as compared with low-rise. Many factors can affect energy use in buildings. But for example, a study of offices in Hong Kong has shown a marked increase in energy intensity with height, mostly attributable to their air-conditioning systems. A similar relationship of height to energy intensity is found in naturally ventilated high-rise blocks of flats in England. It seems possible that these effects are due to increased exposure to the sun and wind in taller buildings: the project will investigate this possibility. By contrast, other studies using simulation models have shown only small effects (or none) of height on energy use.

The project will use empirical data on energy use in tall office and residential buildings in the UK to answer the first of the two questions. Special attention will be given to a small number of boroughs in London - Westminster, the City, Tower Hamlets - in which large numbers of high-rise offices and blocks of flats are concentrated. Individual existing and planned high-rise buildings will be analysed to look at options for rearranging the same floor area in lower buildings on the same sites. The findings will be published as guidance to architects, urban designers, planners and policy-makers, and in the professional and popular press, as well as in academic papers.

IMPACT SUMMARY

If the project should find that there is only a small effect of building height (or none) on energy use, then the impact of that part of the work could be small. This negative finding could be disseminated to an academic audience through papers. The work on density and built form would nevertheless be unaffected, and could be reported to architects and planners as described below. Evidence that energy demand is not a major factor to consider in building height - while environmental and social factors remain important - could nevertheless have implications for planning authorities.

If on the other hand there proves to be a significant effect of height on energy use, the impact of this finding could be considerable. Previous published research by other workers, and some preliminary analysis of existing data, suggests that this may indeed be the case. Many other considerations apply in strategic decisions about built form besides energy use. But if tall buildings do use more energy, this will be an important further consideration for designers and developers.

The results will be important for national policy-making by DECC and DCLG, and could feed into DECC's current work on the National Energy Efficiency Database, and into the Display Energy Certificate scheme. There would also be implications for planners in local authorities. We plan a workshop for policy makers at national and local level, and for the property and construction industries. The Better Buildings Partnership - partners in the project - will play a role in dissemination to these audiences.

Developers and designers of tall buildings will have other agendas besides energy use, which may for them be a minor concern. The belief that 'tall buildings save land' is heavily entrenched. On the other hand there is a growing movement to associate prestige and commercial value with truly efficient energy performance. We plan to reach these professional constituencies with brief articles in the architectural, construction, planning, facilities management and property press. We will attempt to convince architects, urban designers and planners of the issues about density and built form, with a design guide setting out the theoretical arguments, giving illustrations of built form options for specific sites, and presenting generalised results in graphical form. Farrells - also a partner - will participate in the preparation of this guide.

There could be strong interest in the results from the general public and the popular press. The issue of tall buildings and their visual intrusiveness has become highly topical and politicised in the UK, especially in London, in recent years. We plan to reach this audience through the popular media.

We will also publish academic papers and present at conferences in the normal way. This should make it possible to reach international researchers interested in the issues of tall buildings, density and energy use in their own countries.