City Evolution - digital
Demolition, adaptation and retention
The way in which older, not just 'historic' stock is reused to address these issues is an important challenge and one that is essential if we are to develop smarter policies for the future. The work of the 1950s activist Jane Jacobs's is now standard reading for those involved in smart cities debate with Anne Power's work, at LSE who lke Jacobs has fought against large-scale demolition policies and a more bottom up approach. .
Demographic change, environmental targets and the need to maintain a strong economy will depend on minimising demolition, increasing adaptation and precisely monitoring levels of new build.
Population growth and infrastructure development, carbon reduction policies and international competition between cities are likely to increase pressure on older stock. Rethinking (and in many cases re-presenting arguments put forward over the last century those within the conservation movement and urban economists such as Jane Jacobs and Anne Power)
Monitoring and understanding rates of demolition and replacement of London’s stock is therefore likely to become increasingly important.
Peter Bibby (2009) in his analysis of changes to land use in Britain states that ‘A prime insight of urban morphology (and one which is not limited to urban contexts) is that uses change more rapidly than buildings, and buildings change more rapidly than land parcels’. To this could be added road networks, which it is argued, change more rapidly than land parcels, and occupancy, which changes less rapidly than building use. This creates a hierarchy of change, with occupancy at the top and road networks at the bottom. It is hypothesised that when disruption to this hierarchy occurs, ie when one component is replaced at a faster rate than that above it, long-‐term damage to a city will result.
Roman and Medieval roads still form the oldest networks in London. These function not only as principal transport routes but also as the trunk and branches from which London’s streets have formed; areas where most frequent renewal occurs.
Despite relentless development in the Victorian period a remarkable amount of Medieval and Tudor stock survived in London until around 1900. However in the first half of the 20th century the rate of change of land parcels and buildings accelerated, driven by commercial development, new materials and slum clearance. By mid century thousands of buildings had also been bombed or demolished in the aftermath of World War 1112.
During the 1950s and 1960s a rapid rate of change, driven by post-‐war development, began to disrupt Bibby’s hierarchy. A critical factor was the repositioning of the car over the pedestrian. As a result traffic planners rose up the decision-‐making hierarchy. New roads were created and large comprehensive schemes replaced ancient networks and period stock, though London fared better than many historic cores.
From the 1970s onwards the balance of processes began to be redressed as planning departments developed specialist conservation teams. Rates of demolition slowed, designation rose, and many developments were scrapped in the face of local opposition. However the failure of politicians and planners to balance demolition, adaptation and new build, and to understand the relevance of hierarchy, had long-‐term financial, economic and social implications for London and other cities.
In the 1990s Bibby’s hierarchy was challenged again as planning regulations in the City of London were relaxed. The rush to build taller corporate structures led to an increase in the rate of change of buildings. This rate, it is estimated, equalled, and in some cases outstripped, change to building occupancy and use.
4.0 Amenity societies and urban knowledge
It is hypothesised that knowledge of an urban area is proportional to the number of hours spent within it. A community’s empirical knowledge however is rarely fully exploited. This knowledge is represented by the residents and architectural historians who make up local amenity societies, bodies with an intimate understanding of the impact of change.
Though rates of demolition are not tracked by local authorities, amenity societies do monitor loss of stock. The Fitzrovia Society’s records, for example, show that around 8% of its 1km 2 area of prime Central London is proposed for demolition, or has been demolished over the past several years (Figure 2).
Figure 2. Map of Demolition/Construction in Fitzrovia 2014. (Fitzrovia Society, 2014)
During the 1960s and 70s amenity societies across the country predicted the social and economic impacts of comprehensive development programmes, from Covent Garden and Soho, to Spitalfields and Bath.16 Their work led to thousands of buildings, spaces and ancient networks, in these now high Gross Value Areas (GVA), being saved. This proven track record of predicting the impact of future development and requisite constraints represents, it is argued, a consensus of truth. Despite this, recent campaigns to save over twenty unlisted 18th century buildings in London,
15 This estimate is based on empirical evidence gathered by Polly Hudson during campaigns to protect buildings in Shoreditch from high rise development, by the Hackney Society 1995 to 1996
16 Almost Lost. Soho, Covent Garden, The Clapton Animation
three in Goodge St17 and seventeen in Dalston Lane18, have failed.
Repositioning amenity societies at a higher level within the decision-‐making hierarchy, and exploiting their knowledge, is necessary if intelligent long-‐term decisions regarding the makeup of London’s stock are to be made.
Figure 3. GVA values in London 2012, (Office for National Statistics)
5.0 Economic value and uniqueness
Since the 1990s economists have begun to acknowledge the economic significance of heritage assets, and to model their value. The World Bank’s publication ‘The Economics of Uniqueness’ (Licciardi and Amirtahmasebi, 2012) argues that these assets make a city unique and are important for economic growth. The Bank also raises the question: ‘Can a decline in different types of stock be compensated by increase in other stock so the economy’s aggregate capital stock is maintained?’.
It is broadly estimated that around 15% of London’s residential stock has either Listed Building or Conservation Area status19. A clear correlation between house price and designated stock is shown in Figure 4. London’s largest developments,
Figure 4. Below: London House price map (Savills 2013). Above: London’s designated stock (English Heritage. Accessible through Almost Lost Online)
High capital value of older stock however is not limited to designated assets. A recent assessment by property agents Huntly Hooper (Huntly Hooper, 2014) found that luxury period properties in central London rose by 30 percentage points more than high-‐end new build flats over a five year period, with lower value Victorian stock also increasingly sought 21.
London and other successful cities need to attract and retain highly skilled workers (Overman, 2013). As we have seen period properties in London have a high ‘attractiveness’ value. A connection can also be found between UK cities that are
successful at attracting those with higher qualifications and the value city authorities attribute to their historic assets (IHBC, 2006). Figure 5 takes a random area of Camden and sets 2011 census data for higher qualification against date of stock22.
Highest qualified occupants (red) are shown to reside in the oldest properties (blue), lower qualified (yellow) in the newest (green).
Diversity is essential for life. In the natural world the complex way in which diverse organisms interact is fundamental to the creation of balanced ecosystems. Cities also possess complex interdependent systems, developed over shorter timescales, which as argued above, can be disrupted when hierarchies are displaced. The argument that diversity in cities is essential for sustainable economic growth has gained traction over recent years23.
Diversity in street patterns, building morphology, façade detail, land use, and inter-‐ building space all contribute to attractiveness and usability values as indicated by Figure 6. Older stock also offers a spectrum of spaces and rent levels. This is essential to foster small businesses, creative industry and innovation and is unable be provided by new build because of the high yields required 24. Despite this, the value of diversity is still not understood by planners, as demonstrated by the current local outcry against proposed large-‐scale development in Shoreditch, London’s techno-‐ innovation hub25.
Period stock, whether designated or not, is a finite resource. Demolition is irreversible. Though diversity in general age of stock is, to an extent, acknowledged to be of importance, little attention has been given to the role of specific periods in creating economically successful areas. Failure to analyse the potential value of period and morphology will, it is believed, ultimately result in loss, or extinction, of assets of long-‐term worth.
Retrofit and emission reduction within the construction industry are new complex constraints in the equilibrium equation. How could analysis of stock date contribute to this agenda?
The UK Green Building Council estimates that 87% of stock will still exist in 2050 (UKGBC, 2015) though the actual amount of retrofit and demolition required to meet energy targets is unclear (Crawford, et al., 2014, p.7-‐8). 1.5 million low/zero carbon new dwellings are also required, to be created through conversions and new build.
Recent research at UCL has concluded that there is a growing body of research to show that ‘extending the lifecycle of buildings by refurbishment is preferable to demolition in terms of environmental, social and economic impacts’ (Crawford et al, 2013, p.62). Stockdate maps, which allow different construction types within a local authority’s stock to be rapidly geo-‐located, and retrofit costs to be more easily assessed, have potentially a significant role to play.
8.0 Background to the Conservation Sector
The building conservation movement represents a conscious attempt to prevent loss and extinction within the building stock. During the 20th century protection through designation was a reactive process, intimately linked with threat. The higher the level of threat towards a group with similar characteristics the greater the likelihood of protection/ designation.
As with environmental conservation, this reactive approach resulted in latency, with designation lagging behind large-‐scale loss. Substantial levels of demolition to pre-‐ 18th sites occurred around 1900; to Georgian buildings in the 1920s/30s; to Victorian buildings in the 50s/ 60s and to post-‐war buildings in the 80/90s. These formed critical points in designation history with new legislation and new designation categories triggered by each demolition wave26.
The probability of a building being designated (ie protected from demolition) has, historically, been related to the distance of its date of construction from the present day, and its rarity value27. The ratio of designated buildings from a specific period to total extant stock from that period, is also proportional to the period’s distance from the present day28 .Though rates of designation have declined since the 1970s, the number of protected buildings has substantially increased29.
Lack of investment in new technologies, and insufficient cross-‐sector collaboration, has however left English Heritage out of sync with other sectors. Radical change is needed to the anachronistic way in which designated data is recorded. Re-‐ classification of all designated assets and a complete overhaul of the National Heritage for England digital database are urgently required.
Phase transition within the organisation could however take place during its transfer to Historic England in 2015. English Heritage has an outstanding historical knowledge base, intimate understanding of the impact of change and significant experience in sustainable work. This puts it in an ideal position to oversee stock analysis by local authorities and research into rates of change.
The organisation’s Heritage Landscape Characterisation programme (HLC)30, which since the 1990s has been digitally characterising England’s landscape in aggregated form, also represents pioneering work in the field of big data. Raising the status of HLC however will be essential to effecting phase transition and to raising Historic England’s position within the decision-‐making hierarchy.
11.0 Summary and Conclusion
Successful, sustainable cities rely on balancing the construction, conversion and demolition of their stock. However an understanding of the underlying hierarchies that enable balance to be achieved is also necessary. Calculating and calibrating rates of change within London’s stock has the potential to maximise diversity, efficiency