URBAN DENSITY, SUSTAINABILITY AND URBAN METABOLISM

 

Philip Meadowcroft   May 2001

 

The following essay has been gathered from articles and reports written in recent years by Peter Carl and Cambridge Diploma students.

 

It is generally assumed that our major cities are now undergoing a process of transformation from dispersal to compaction. It is also generally accepted that this process presents a more sustainable alternative as arguments concerning energy efficiency and economy of resources become more developed.  Whilst evidence of this process is widespread there is continuing counter pressure  towards the marketing of lifestyles associated with dispersed urban topographies.  The result, despite sound intentions is that many recent inner city developments retain the characteristics of less urban examples.

 

Presentations of arguments for and against density, appear marked by similar points of reference. The tendency to frame comparisons in quasi scientific (quantifiable) terms reveals the degree to which conceptual strategies of the late ninteenth and early twentieth centuries have become ingrained in planning law, free-market ideals and the customary expectations of developers, technical consultants and architects. Issues of zoning, economy, statistics and formulae of all kinds remain the common language. An inflexible monothematic approach to urban design is the result.

 

Despite the sophistication of present culture the making of ‘good’ towns still seems to elude us.  The beauty of such recurring paradigms – Siena, Padua, Paris for example is only due in part to the work of aestheticians or transport engineers.  Rather it is the processes of conflict and mediation, the capacity to assimilate on-going change within a more permanent context which is of more significance.

 

Accordingly in our work we seek to avoid the quasi-utopian practice of pacifying the urban order, of making it ‘safe’ for desirable activities. Instead, we strive to understand the urban order as the mediation of lived conflict and difference (not to be confused with the term mixed use).  In this sense ‘sustainable’ connotes a welcome return from the idealized vision of highly serviced isolation to greater urban densities and with that a return to a more deeply involving political (participatory) life.  The present reuse and adaptation of existing buildings and urban structures points to another aspect of the phenomenon – that one must think in terms of centuries and consider an order that is both stable and open to various cycles of change.  A city is a permanent receptacle of metamorphosis; permanent with respect to its setting and general layout variously metamorphic in most other respects.  However this metamorphosis is not simply change; there is always an element of recollection, a dialogue between what a city has always been and the most recent transformations – an on going exchange between transition and permanence understood as a metabolism.

 

 

INVESTIGATIONS INTO THE METABOLISM OF THE URBAN ORDER

 

If urban renewal is equated with density then an understanding is required of the possible structures and processes of density. Urban order is understood as a strata of processes, which manifest transformation across a range of timescales.  Some of these processes of change span centuries others decades even years. The structure of these processes is termed ‘urban metabolism’

 

Through teaching I have been involved in on-going research being carried out by Dalibor Vesely and Peter Carl at Cambridge University Department of Architecture. This research has been concerned with the phenomena of the traditional European urban block as a paradigm for the interpretation of contemporary urban situations which has been the focus for design work of our students.

 

PRECEDENTS

 

In our search for an alternative to the dispersed and fractured topographies of the post war city the medieval city remains the single most pervasive paradigm.  It is not the appealing vision of complexity and ‘beauty’ which is informative but the processes by which it arose. In particular its ability to metamorphose through time and throughout sometimes radical cultural change.  This capacity has allowed them to assimilate quite extreme technological change without significant trauma to the existing complex fabric or patterns of life.  By comparison cities which have been ‘tailor-made’ to accommodate these new technologies have soon become lacking or redundant. 

 

It is ironic that the medieval city topography is a focus of so much theory and yet came about without the aid of theory.  It is also revealing that both theory and practice have shown an incapacity to cope with the ‘messiness’ of their own most durable paradigm.

 

Of course there is no question of a return to medieval conditions nor an imitation of such topographies. However, in their present transformed state certain examples clearly succeed as cities of compact density.  At the very least there may be lessons to be learnt which may inform contemporary alternatives. For this reason they have been worth investigating in detail.

 

For an understanding of the metamorphic processes at work our investigations have lead us to consider the city at the scale of the urban block.

 

 

INVESTIGATIONS INTO THE METABOLISM OF THE URBAN BLOCK

 

Between 1997 and 1999 students of Diploma Studio 1 carried out research into the urban block structure of Cambridge / Padua and Como as background research for their urban proposals.

 

The studies involved historical analysis of the cities and their parts followed by numerous city walks and comprehensive mappings of a number of representative urban block structures within various critical locations.  The mappings included exhaustive recordings of the activities (both historic and present) within each block, photographic surveys and descriptions of spatial relationships both internal and external.   The following examples are extracts from documents compiled by our students.

 

In contrast to modern block types the historic urban block is characterised by a deep hierarchical structure from perimeter (public) to interior towards degrees of privacy.

 

We use the term ‘depth of block’ to refer to the structure of density of the block and second in a metaphorical sense to suggest the richness and diversity of life sustained by the block.  The term metabolism has been applied to describe the interrelatedness – both temporal and topographical of the more or less autonomous activities which the block supports. 

 

COMO

 

An example of this was traced in the Via Milano, Como, blocks where there is an ‘official’ culture on the streets – commercial, offices, clinics, (higher rent activities or public / civic which require a visible presence) : behind which is an ‘unofficial’ culture inside the block of the most extraordinary changing diversity. One cannot make a town of either the or unofficial on their own but rather one needs the whole metabolism – the ‘unofficial’ culture is crucial to the depth and richness of the town.

 

The blocks that were studied reveal a spectrum from a very dense order (generally closer to the historic centre of the city) with courtyards occasionally the size of rooms to more amorphous blocks consisting of an agglomeration of medium sized edifices.  In between are structures where a range of public and semi public spaces are hidden within and penetrate through the block interior.

 

In general terms the fabric and activities on the perimeter have remained more stable over time. Notably (in the most part nineteenth century) frontages onto the main artery (Via Milano) are consistent.  However behind these more linear facades lies a more varied configuration of buildings and uses which evidently change more rapidly – these include more specialised shops, workshops (car repair, fabrication), a bus depot, private houses, schools, institutions with gardens, modern residential buildings with garden courts, professionals offices and small industries plus many more.

 

Corresponding differences were recognised in terms of the daily cycle of activities as one penetrates the layers of the block.  The perimeter remains active throughout the 24 hour cycle, the activity of the interior is more dependent upon opening and closing times with pockets of almost permanent tranquillity (shared residential gardens).  Various segments - the area around the school - for example may be extremely animated for short periods and then subside.

 

The degree to which the hierarchical structure has been retained over time is striking.  There is a consistent differentiation between front and back, exterior and interior. The degree to which penetrable layers occur allows for a vast range of conditions and activities.  At the same time the hierarchy of secondary streets, arcades, alleys, courtyards and gardens maintains the dialogue across the whole depth.  At no point is public life entirely excluded.

 

 

CAMBRIDGE / PADUA

 

In 1997 we instigated a comparison between Cambridge and Padua.  This was in response to the debate concerning the current proposals for expansion of Cambridge.  The two cities are similar in identity, both are historic cities undergoing radical growth, both are of comparable population but vastly different scales .  Padua occupies approximately 1/3rd of the area of Cambridge.  Our project for the year was entitled ‘Cambridge 3000’ and speculated upon the densification of Cambridge through a long term process of metabolic growth.

 

Padua Urban block metabolism analysis.

 

In general terms we identified two types of urban block, with variations, in our survey of Padua:

 

  1. Centre city block of approximate dimensions 50-80 metres are typical of any dense Italian mediaeval / renaissance city. Existing as 5-6 storeys they are about twice as high as their Cambridge counterpart with block interior spaces that range from Cortili to terraces and light wells.  Their occupation is vastly more diverse than Cambridge and changes with an approximately generational frequency.

 

Against the modernist vision of flexible space usually conceived in terms of deep plan highly serviced floor plates (concrete frames) the masonry construction of these blocks allows for rapid and inexpensive reconfiguration and adaptation – dwellings can easily transform into offices, shops, clubs, bars, small workshops and so on.   Each block is characterised by several of these activities (and more) existing alongside each other in any given block.

 

  1. The second type of block is much larger at least 150 metres long x 100metres,  up to 400metres x 200 / 250 metres,  and found between the XII and XIV century walls.  These blocks are similar in outward appearance. The difference is seen inside the block where one can distinguish several layers of depth developing back from streets. These layers support activities ranging from dwellings, playgrounds, and schools, through to University departments and even local headquarters of the local electricity company.   Accordingly they change character from one end to the other. The interior of the block is typically one or two gardens with car parking below ground. They present a considerable change in physiognomy across the section and in scale even allow for the development of small interior streets. The whole interior is rarely available to all the surrounding buildings rather there is a great variety of shared and private segments and modes of traversal from complete occlusion through narrow lanes to public gardens. 

 

There is only one block of such size and approximate complexity in Cambridge  - which brackets the cemetery between 2-storey domesticity of Gwydir Street and Anglia University.  In the most part Cambridge is characterised by low rise residential blocks or denser blocks dominated by exclusively University uses.

 

 

SUMMARY / CONCLUSIONS

 

From our findings in relation to the mappings three themes deserve remarking upon:

 

 

  • The role of measures: What sort of activities can be supported by what dimensions and where in the larger urban metabolism one finds the blocks that support different scales of activities.

  • The role of the history of evolution of these configurations – the cycles of exchange between the permanence of the block and the metamorphoses of the situations and architectural settings.   At the same time the content of the block is less dependent upon history than it is upon the measure.

 

  • It is evident how lack of sensitivity to the block from the latter third of the XIXth Century to the present creates dead zones of non-specific content.  This is evident in the modern housing blocks (Como) whose height is less a difficulty than what happens on the lowest storeys but also in recent office/shop arrangements whose orchestration of ‘semi-public’ space once again confuses architecture with urban structuring and creates spaces which are neither ‘here nor there’

 

We recognise that the urban/architectural order is only the background to the active life of the city, but that this background is part of what is always present for everyone, therefore part of the deposit of tradition, the context for history.  At the next level of understanding, that of the city as mediation of conflict, the phenomenon of block depth and structure seems the most propitious for providing a matrix that is sensitive to the intermediary process between particular requirements and those of the whole, as well as of the need to provide a topography that is sensitive to the several cycles of history that lie between permanence and transience.