How can urban densification be defined, monitored and controlled to create positive outcomes and avoid unintended consequences / negative impacts?

Guest editor: Jacques Teller

This special issue investigates the specific challenges, impacts and fragilities that urban densification creates in many cities and the different scales where these can be found. It questions the hegemonic discourse in favour of urban densification and proposes a more nuanced and holistic view of its costs and benefits. Although urban densification may provide several social, economic and environmental benefits, it also requires assiduous monitoring and regulating by public authorities and urban planners to promote resilience and reduce fragilities.

This special issue investigates the specific challenges, impacts and fragilities that urban densification creates in many cities and the different scales where these can be found. It questions the hegemonic discourse in favour of urban densification and proposes a more nuanced and holistic view of its costs and benefits. Although urban densification may provide several social, economic and environmental benefits, it also requires assiduous monitoring and regulating by public authorities and urban planners to promote resilience, reduce fragilities.

Definitions of urban densification have varied in the past and were different factors: indoor density, parcel density (floor area ratio), residential neighbourhood density and citywide density – each category containing several different metrics. One series of papers in this special issue is related to the measure of urban densification, considering both past densification and potential one. This new clarity of definition and measurement embraces a multifactorial set of indicators so as to disentangle the different dimensions of density, and their evolution over time. Urban policymakers and planners will benefit from these new approaches.

This special issue’s contributions also investigate, analyse and provide evidence on urban densification in a multidimensional perspective, considering economic, social and environmental factors that impact at different scales. Resistance to densification can be related to:

• socioeconomic issues: defending the rights of existing communities to maintain a low density in order to preserve affordable housing or local workplaces, etc.
• environmental issues: the protection of green areas included in already dense areas
• morphological issues: cadastral inertia and difficulties in plot reallocation for larger development

These different factors also have a spatial justice perspective, balancing the individual and collective costs and benefits of densification. Several papers address the social and economic dimensions of urban densification, adopting a critical perspective as regards its motivations and outcomes.

The papers published in this special issue converge in depicting urban densification as a complex, non-linear process, which has to be addressed at various scales and across time.

A critical issue for urban planners and decision-makers is addressing both structural and functional density, as well as making clear distinctions. Observed discrepancies between both dimensions over time and place are highly instructive of existing urban challenges, may these consist of overcrowding, speculative behaviours or building dereliction.

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Table of Contents

Regulating urban densification: what factors shouldbe used? [Editorial]
J. Teller

Compacting the city centre: densification in two Newcastles
B.Giddings & R. Rogerson

Urban infill development potential in Germany: comparing survey and GIS data
G.Schiller, A. Blum, R. Hecht, H. Oertel, U. Ferber & G. Meinel

Housing growth: impacts on density, space consumption and urban morphology
F.Kostourou

Urban form and liveability: socioeconomic and built environment indicators
N. Martino, C. Y. Girling & Y. Lu

Density and morphology: from the building scale to the city scale
D.Godoy-Shimizu, P. Steadman & S. Evans

Planning for residential ‘value’? London’s densification policies and impacts
N. Livingstone, S. Fiorentino & M. Short

Conceptualising urban density, energy demands and social practice
J.Rinkinen, E. Shove & M. Smits

Anatomy of density: measurable factors that constitute urban density
S. Angel, P. Lamson-Hall & Z. Gonzalez Blanco

Urban densification and social capital: neighbourhood restructuring in Jinan, China
X. Li & M. Sunikka-Blank

Urban density and Covid-19: towards an adaptive approach
J. Teller

Systematic review and comparison of densification effects and planning motivations
M. Berghauser Pont, P. Haupt, P. Berg, V. Alstäde & A. Heyman

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Abstracts

Regulating urban densification: what factors shouldbe used? [Editorial]
J. Teller
https://doi.org/10.5334/bc.123

Urban densification is increasingly accepted as a necessity and is important for no-net land take. Densification occurs in many places, especially fast-growing cities with a combination of demographic change, economic pressure and large transport infrastructure projects. The costs and benefits of density require a nuanced understanding: potential direct, indirect and cumulative effects (environmental, economic and social), both on- and off-site. The optimisation of densities implies a need to identify the conditions that can create the most value for the city, identify the places most appropriate for future inhabitants and activities, and promote spatial justice. The papers published in this special issue converge in depicting urban densification as a complex, nonlinear process, which has to be addressed at various scales. Multifactorial metrics of density are superior to aggregated ones because they offer a better understanding of the urban forms and how they are experienced by inhabitants and users. Both hard and soft densification have to be duly monitored and regulated if cities are to avoid overcrowding of places and buildings, which can be detrimental to urban resilience. The relation between urban densification and housing affordability is a critical factor that policymakers must address.

Compacting the city centre: densification in two Newcastles
B. Giddings & R. Rogerson
https://doi.org/10.5334/bc.74

The compact city and the associated process of densification have attained almost hegemonic status as a sustainable urban form. Seeking to counteract the negative impacts of sprawl, urban densification has usually focused on areas beyond the city centre. However, a renewed attraction of the urban core is altering patterns at a time when other trends, including the decline of retailing and commercial activity, are also changing demands for space in the city centre. This paper investigates different approaches to the use of urban densification as part of strategies for the regeneration of the city centre. Drawing on two case studies—Newcastle upon Tyne in the UK and Newcastle in New South Wales, Australia—it considers the different mechanisms by which city authorities and their development partners are seeking to densify the city centre, and examines the tensions created by the process in these two contexts. In addition to document analysis, data are derived from symposia based in both cities as part of the future of the city centre project led by the authors. Contributors included representatives from local government, non-government organisations, business and community groups. The outcome is an appraisal of contrasting approaches to the densification of city centres.

Policy relevance: Coherence of city form and consistency throughout the city centre are important objectives, and great differences in density disturb this unity. The city centre is not a project, but a continuous process. Thus, it benefits from fine grain developments on the principle of a rich built environment being generated through small contributions by numbers of people over time. A concept is proposed that densification has positive outcomes up to a point at which negative effects begin to occur. Density is readily measured, but the question remains where the balance point is for each city. There is also a notion that negative impacts may occur before a stipulated density is realised. Support is needed to develop a virtual city model for all cities, and funding to advance city information modelling for all aspects of sustainability, to encourage optimum levels of densification to be achieved.

Urban infill development potential in Germany: comparing survey and GIS data
G. Schiller,A. Blum, R. Hecht, H. Oertel, U. Ferber & G. Meinel
https://doi.org/10.5334/bc.69

Limiting land take is an important sustainability target. To this end, infill development is a primary strategy. To implement this strategy, policy-makers need a reliable knowledge base on infill development potential (IDP), such as brownfields, vacant lots and underused lots. This study presents the results of the first comprehensive national survey of IDP in Germany. Almost 12% of German municipalities were contacted by questionnaire. In contrast to previous studies, this study also takes into account smaller towns and small-scale vacant lots, which would otherwise lead to a considerable underestimation. Additionally, a feasibility study shows how IDPs can be identified using a geospatial approach. Here, a procedure is presented that allows the identification of IDPs and the differentiation between vacant and underused lots by analysing urban morphology using nationwide and commonly available geospatial base data. The results provide a good basis for an initial inventory. However, to obtain more accurate results, additional specific data would be required, the accessibility of which is currently limited. With the development of an improved spatial data infrastructure combined with Open Data initiatives, geographical information system (GIS)-based procedures for the automated detection and monitoring of IDPs could become more important in future.

Policy relevance: If the objectives of land policy, especially the avoidance of urban sprawl, are to be achieved, more efficient use of already developed land is essential. At the strategic level of policy development, knowledge of land suitable for infill development is as necessary as knowledge of the land take. Currently, regular standardised questionnaire surveying is the effective method for analysing infill development potential (IDP) and its development on a large scale. Geospatial approaches can help to identify potentials, especially on vacant and underused lots. Thus, they have a considerable potential to serve as heuristic tools for local practitioners seeking to begin reflecting on infill development options. Policy-makers and planners should recognise this potential and develop it further in cooperation with the scientific community. However, decision-makers are not spared from weighing the appropriate density in the respective context—and this has not become easier under the impact of the current COVID-19 pandemic.

Housing growth: impacts on density, space consumption and urban morphology
F. Kostourou
https://doi.org/10.5334/bc.75

How and why do houses densify over time? What is the impact of that growth and what kind of constraints affect their potential to change? This research explores built form change and densification, providing historical evidence from the incremental transformation of a 19th-century housing scheme, Cité Ouvrière, in Mulhouse, eastern France. This granular longitudinal morphological study uses historical planning applications and images to map the external volumetric transformations of 1253 single-family houses over a 165-year period. The research combines archival work with three-dimensional (3D) architectural modelling and an advanced density method to record, visualise, analyse and evaluate the densification process at the microlevel. Statistical computing traces the densification process and the Spacematrix tool analyses the impact on open space consumption for different building typologies and for the neighbourhood as a whole. The results highlight seven types of transformations, affected by seven drivers of physical change. Densification is manifested either through built intensification or plot union/subdivision, and its degree is determined by the extent to which non-built space is consumed. These depend on socioeconomic, legal and physical constraints imposed by the original design.

Practice relevance: This work informs architects and planners how the design of houses together with non-formal constraints affect buildings’ resilience and longevity and their capacity to accommodate growth over time. By tracing the successful transformation of a suburban settlement to a dense and morphologically diverse city quarter, the results support the slow and contained densification of existing housing through small changes—an approach which can benefit the sustainability and energy agendas of cities and settlements in Europe and abroad. This expands the current understanding of built density, advances our knowledge in the simulation and forecasting of dynamic change in the building stock, and contributes methodologically to the fields of urban morphology, geography and data computation.

Urban form and liveability: socioeconomic and built environment indicators
N. Martino, C.Y. Girling & Y. Lu
https://doi.org/10.5334/bc.82

Spatial relations among urban elements (buildings, streets, etc.) constantly affect the quality of urban spaces, creating more or less livable cities. The study of urban form has been a way of objectively quantifying such relations to understand their dynamics. Urban livability is the ability of urban spaces to fulfill the expectations of its inhabitants for wellbeing and quality of life. Measurable spatial patterns underlie the emergence of livable cities. Still, few researchers have considered if and how these patterns affect socioeconomic conditions across spatial scales. This paper explores the relationships between indicators of socioeconomic livability and cross-scale patterns of demographic and morphological densities within the Metro Vancouver (MV) region (Canada). Indicators of accessibility, social diversity, affordability, and economic vitality were quantified and compared among five population density clusters composed of 3450 census dissemination areas (DAs) in MV. Morphological indicators of intensity, centrality and diversity were aggregated at the DAs using spatial network analysis with five radii from 400 to 4800 m. Socioeconomic indices were regressed on urban form variables to assess the importance of the built environment on predicting livability-related qualities. Overall, indicators of the intensity of urban form were the most significant to predict the socioeconomic metrics.

Policy relevance: Policies that aim to solve urban issues should consider nonlinear relations among variables. In the case of MV, indicators of accessibility, social diversity and economic vitality are directly correlated with each other and inversely correlated with affordability. Medium to high-density zones presented a fair equilibrium among the different livability qualities analyzed. Attributes aggregated with the 4800 m radius were highly important to predict the livability qualities within a 400 m radius, which potentially means that urban interventions may affect the livability of spaces not immediately close to them. A higher density of buildings with moderate height distributed among parcels with distinct sizes can potentially have a positive impact on economic vitality and housing affordability. The intensity and diversity of the tree canopy was important to predict active accessibility and social diversity. The inclusion of spatial diversity and network centrality measures on urban planning and design practices potentially foster more livable densification processes.

Density and morphology: from the building scale to the city scale
D. Godoy-Shimizu, P. Steadman & S. Evans
https://doi.org/10.5334/bc.83

The density of the domestic building stock of London is explored, moving from the scale of individual house and blocks of flats, through larger geographical units, to complete boroughs. The description of the stock is highly detailed and is made using the 3DStock method which derives building geometry from digital maps and LiDAR (laser measurements from overflying aircraft). This means that accurate estimates of floor areas can be made, and used to measure densities as floor space index (FSI) values. Ground coverage or ground space index (GSI) values are calculated from building footprints and land boundaries. The Spacemate tool devised by Berghauser Pont and Haupt is used to plot types and ages of dwellings in terms of FSI, GSI and numbers of storeys. Figures for actual annual gas and electricity consumption are attached to each dwelling. Analysis shows that, in general, energy use intensities - and especially the intensity of gas use for heating - decrease with increasing density and with the transition between house types, from detached, to semi-detached, to terraces, to (low-rise) flats.

Policy/practice relevance: The findings should be of interest to planners and policy makers concerned with energy use in the domestic stock, and how this may be reduced by fabric measures. The paper provides data on housing densities not previously available in the form of FSI and GSI values. Urban designers and housing architects can gain a fuller understanding of the relation of built form to density, and how these in turn affect energy use.

Planning for residential ‘value’? London’s densification policies and impacts
N. Livingstone, S. Fiorentino & M. Short
https://doi.org/10.5334/bc.88

This paper considers the agency and influence of planning processes and densification policies on urban landscapes in London. Urban transformation through residential densification can bring opportunities for real estate development, combined with longer term investment and financial gains for local authorities through planning gain. However, the measurements and indicators used to define density and its impacts could be better understood both objectively and subjectively through the lens of an extended notion of ‘value’. Such experiences of density can be viewed bluntly as positive or negative. This research investigates nuanced dimensions of density and adopts a primarily qualitative approach, reflecting on relevant literature and wider policy context through a discourse analysis relating to densification in London. The idea of elements of ‘value’ is explored and evaluated in ongoing developments through a detailed case study of Nine Elms, London. Quantitative data on the residential real estate market is used to illustrate investment flows. Conclusions consider best practice policy recommendations in relation to understandings of ‘value’.

Policy relevance: Lessons from London indicate how densification can be a viable option for both urban policy makers and practitioners when approaches adopt a flexible governance and planning approach, embedded in local context. Densification processes in planning and governance should be regularly reviewed and reconsidered in line with broader national and city-wide policies, optimising rather than maximising density. Both subjective and objective measurements should be accounted for, by reflecting on broad and informed indicators. The value created by densification processes should be the result of a weighted and broader assessment of variables: economic, social, and place-specific considerations. However, the often antagonistic, ambiguous nature of density and its application needs to be recognised by policy makers, regulators and actively involved parties (planners, developers, investors) to contribute to the creation of successful places.

Conceptualising urban density, energy demands and social practice
J. Rinkinen, E. Shove & M. Smits
https://doi.org/10.5334/bc.72

In urban studies and in energy policy there is much debate about the relationship between energy demand and the density of residential areas, measured in units such as those of population/ha or population/km². A different approach is presented in this paper. Rather than evaluating the relative merits of compact or sprawling urban forms, the focus is on the spatial configuration of the infrastructures, appliances and systems of provision on which city life depends. An interview-based study of households living in the same extremely ‘dense’ neighbourhood in Hanoi, Vietnam, shows how practices of cooling, laundering and cooking (and the energy demands associated with these practices) are shaped by material arrangements that exist within the home and that also stretch far beyond. The conclusion that supply and demand are constituted across multiple spatial scales has practical implications for urban design, and for how the relation between energy demand and density is defined and understood.

Practice relevance: Energy demand is a consequence of how social practices are distributed and organised across space and time. By contrast, metrics of density can be counterproductive and tend to obscure potentially crucial questions regarding the constitution and the transformation of energy demand. A practical approach is presented to conceptualise relations between material arrangements and energy demands at different scales: from the layout of the home to more extensive infrastructures and systems of provision. The implications of these ideas can influence debates about urban density and design by focusing attention on infrastructures, appliances and the layout of the spaces that influence how they are actually used, and for the practices they accommodate and enable.

Anatomy of density: measurable factors that constitute urban density
S. Angel, P. Lamson-Hall & Z. Gonzalez Blanco
https://doi.org/10.5334/bc.91

Serious concerns about global warming have been translated into urgent calls for increasing urban densities, as higher densities are associated with lower carbon emissions from both vehicles and buildings. However, attempts at effective densification have generally failed and urban densities continue to decline in cities across the world. Calls for densification without making room for it have resulted in serious housing supply bottlenecks in many cities and have rendered their housing unaffordable. If affordable densification is to be successful, it is necessary to understand the factors that constitute urban density. A novel way is presented for factoring the average density of cities into constituent factors—three or seven factors—that when multiplied together reconstitute urban density. This factoring methodology is presented together with the preliminary measurement of these factors in 10 cities in 10 world regions. This approach allows, for the first time, a clear understanding of how different cities acquire their density: Hong Kong gets its density from building height; Kinshasa from crowding; and Dhaka and Bogotá from residential coverage. This anatomy of density offers a new outline for a comprehensive strategy for city densification: one that addresses each and every one of the factors that constitute urban density.

Practice relevance: Urban density is usually defined as the ratio of the total population of a city and its total area. This is the most appropriate single metric for measuring progress in densification in cities and is now a central objective of the global climate change agenda. However, this metric is rather crude and often hides more than it reveals. The anatomy of density offers a new, simple method for factoring urban density into its constituent factors that when multiplied together reconstitute urban density. This approach offers city leaders and urban planners a new way to consider and develop a comprehensive policy options and strategies for city densification: one that addresses each and every one of the factors that constitute urban density and the tradeoffs between them.

Urban densification and social capital: neighbourhood restructuring in Jinan, China
X. Li & M. Sunikka-Blank
https://doi.org/10.5334/bc.70

Urban densification and massive restructuring projects in China have dictated profound socioeconomic changes. This paper explores changes in social capital and residents’ daily practices (cooking, eating, cleaning, shopping and socialising) in Jinan, Shandong province, after their low-rise courtyard dwellings were demolished and replaced with high-rise apartments. At the neighbourhood scale, privatised practices have reduced the use of urban streets and communal facilities. At the building scale, a transition for long-term residents from a courtyard housing typology to high-rise has led to a radical change in their daily practices that has moved from outdoors to indoors. Such changes have increased privacy and reduced social relations and social capital in the neighbourhood. These residents continue to maintain very close relationships with each other, but this can exclude ‘newcomers’ who have moved to the neighbourhood after the restructuring—an outcome regarded as the ‘dark side’ of social capital. Residents in high-rise flats have developed a preference for privacy and increased use of indoor spaces for activities such as sleeping, cooking, eating and socialising. By showing how urban densification changes material arrangements and residents’ practices and social interactions, the study reveals the unintended consequences of policy-driven densification in China.

Policy relevance: This research reveals the unintended impacts of urban densification on neighbourhood social capital and the division between ‘stayers’ and ‘newcomers’, underlying the importance of social sustainability when planning urban restructuring projects in China. Three recommendations are made for policymakers. First, residents’ lived experiences and social impacts are vital for planning urban restructuring. The utility of urban spaces can generate social capital, which improves the social sustainability of the project. The courtyard house typology encourages more outdoor activities and social interaction than the high-rise typology. Decisions made at the neighbourhood level and about density will impact the local residents. Second, the categories of ‘stayers’ and ‘newcomers’ can be used to better understand the diversity of practices and neighbourhood social capital, instead of limiting to demographic indicators, e.g. income levels. Third, residents’ appreciation of the gated communities makes it more difficult to implement the current government policy of opening the gates.

Urban density and Covid-19: towards an adaptive approach
J. Teller
https://doi.org/10.5334/bc.89

A literature review and analysis is presented on the influence that urban density has on the diffusion of Covid-19. Six main categories of factors are identified: urban settlement, socioeconomic factors, urban services, urban environment, policies and time. At this stage there is no scientific consensus about the effect of density. Urban connectivity appears to play a bigger role in the diffusion of the pandemic. Important gaps are identified in the literature on the compared governance of risk and the density at the building level. More research should be directed to the evaluation of adaptation measures adopted by cities, communities and individuals. The relation between urban density and health issues should be framed in a vulnerability perspective, considering the interplay between exposure, sensitivity and the adaptive capacity of cities.

Policy relevance: Given the lack of consensus between scientific studies, it is too early to reverse the existing policies and recommendations that promote dense and compact development. Instead, more attention should be paid to the types/conditions of density and the equitable access to urban services and green infrastructures in order to minimise risks and lower the burden of social-distancing measures in dense environments. Resilience policies should focus on addressing deficiencies in the existing urban environment that are at the core of the epidemic outbreak. These policies should be based on a close collaboration with local communities and intermediate actors (e.g. planners, architects, health officials, etc.) to address social, economic and technological inequalities.

Systematic review and comparison of densification effects and planning motivations
M. Berghauser Pont, P. Haupt, P. Berg, V. Alstäde & A. Heyman
https://doi.org/10.5334/bc.125

Do higher urban densities contribute to more sustainable cities and communities? This paper examines the effectiveness of higher density (as a means) for achieving sustainable urban development (the goal) following three lines of enquiry. First, a systematic literature review of scientific literature (n = 229 peer-reviewed empirical studies) is presented on the effects of urban density at different density thresholds and city sizes. Second, the motivations for increasing urban density are studied in a systematic review of Swedish planning practices based on the comprehensive urban plans in 59 municipalities. Third, these two studies are compared to find matches and mismatches between evidence and practice. Although the positive effects exist for public infrastructure, transport, and economics, there are also considerable negative environmental, social and health impacts. This creates a challenging task for urban planners to assess the trade-offs involving densification and accommodate current urbanization rates. Some topics are found to be over-represented in research (transport effects), seldom discussed in practice (environmental impact), and misaligned when comparing motives and evidence (social impact). Furthermore, for some topics, urban design thresholds are found that are important because they may explain some of the divergences in the results between studies.

Practice relevance: The transfer of knowledge from research to planning practice is a serious concern as planning strategies are not aligned with scientific evidence. Planning practice in Sweden is more positive about the contribution of higher density to sustainable urban development than the results of empirical studies warrant. The largest deviation is found in relation to social impacts of higher density where the planning arguments are not aligned with the evidence. Several reported negative effects of densification (e.g. water management, recreational infrastructure, biodiversity) are not sufficiently accounted for in Sweden’s planning policy and strategy. The narrow planning focus on decarbonising cities and densification needs to be broadened to ensure cities are resilient against the effects of climate change and include social, environmental and health impacts. The findings can be used to develop evidence-based planning strategies.Other countries can apply this process to assess their planning strategies.

Keywords: cities, densification, sustainable urban development, systematic review, urban density, urban planning, Sweden

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