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The analysis of Urban Form as an assessment tool of Sustainability

Extented abstract of dissertation for the degree of Master Civil Engineering

Quentin José Manuel Blanpain Silva

Instituto Superior Técnico, Lisbon, Portugal

July 2015

Abstract. This thesis aims to establish a procedure for assessing the sustainability through analysis of the

Urban Forms. In this sense they are chosen two case studies which intend to exemplify the method used,

checking their relevance for evaluating Urban Sustainability and, on the other hand, to test its utility by

selecting and quantifying parameters in urban areas with different characteristics and periods of origin.

The Urban Form analysis of the historic center of Évora allows you to apply the method of Urban Structural

Units, based on the methodology by Paul Osmond (Osmond, 2008). This method provides an analytical tool

and diagnostics of the built ambient of the historic center and establishes a basis for the evaluation of the

Urban Metabolism.

In the second case study, USU’s are selected in seven areas of Lisbon, representing the principal moments of

the urban development in the city. The quantification of indicators, based on the range of parameters

established by Serge Salat (Salat, 2011) allows to evaluate and compare Urban Sustainability of the selected

zones, by analyzing the energy consumption of buildings. A detailed statistical analysis allows to evaluate the

relevance and consistency of the indicators used and prove the scientific validity of the USU’s method in the

assessment and measurement of Sustainability.

Tags

Urban Morphology, Urban Sustainability, Urban Metabolism, Urban Structural Units

The main objective of this thesis is the Urban Morphology analysis of built tissues, with different

shapes and periods of construction, for the assessment of sustainability. In order to achieve this goal,

the following objectives were defined:

1) Systematizing the methodologies of Urban Form analysis.

2) Apply the method of Urban Structural Units, developed by Paul Osmond (2008) and evaluate

its utility for the Urban Sustainability assessment.

3) Establish a methodology that allows the comparison of the Sustainability of urban areas with

different periods of origin.

4) Determine the relevance and future possibilities in the application of the methodology used in

this work and the USU’s methodology for Urban Sustainability assessment.

The methodology of Urban Structural Units, by Paul Osmond (2008), is applied to the historic center of

Évora, allowing a critical analysis of the utility of the methodology for the analysis of Urban Form in

general and a first approach for the Urban Sustainability assessment.

The Urban Sustainability assessment is performed by choosing USU’s within seven urban areas of

Lisbon, which characterize the main periods of the development of the city. Relevant indicators for Urban

Sustainability assessment are chosen from the range of parameters established by Serge Salat (2011),

which main objective is evaluate the energy consumption of buildings.

A critical evaluation of the relevance and consistency of the results is assessed through statistical

analysis. A sensitivity analysis allows to sustain these analyzes and check the homogeneity of USU’s.

1 Introduction

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There are different perspectives and approaches in the analysis of Urban Form, characterized by

the Anglo-Saxon, Italian and French schools (Moudon, 1997). The Analysis of the Urban Form in this

thesis lies in Anglo-Saxon approach.

The Anglo-Saxon school has a descriptive, analytical and explanatory approach and offers the

most complete and detailed type-morphological method of the three schools (Moudon, 1997).

This school initiate with M.R.G. Conzen’s works, who developed in more detail the morphological aspect

of the built environment, called Townscape. Conzen recognized the tripartite division of the Townscape:

Town Plan, Building Fabric and Land and Building Utilization (Whitehand, 2001). The Town Plan is

constituted by four elements: Site, Street System, Plot Pattern and Building Arrangement.

Conzen defined the concept of Plan Units as a combination of the Street System, the Plot Pattern and

the Building Arrangement, which constitute the Town Plan. These elements are grouped and organized

in different combinations constituting different units with a "morphological homogeneity". On a larger

scale of the Town Plan, Conzen identified Plan Divisions as combinations of Plan Units. Conzen also

defined the concept of Morphological Regions, as homogenous areas in terms of its form, which

distinguish them from other surrounding areas (Whitehand, 2001).

The methodology developed in this school aims to identify and classify buildings in "Types". In

this approach, a city consists of Basic Types (dwellings) and Specialized Types (churches, palaces…)

(Pereira Costa, Stael de Alvarenga, Safe, & Cleide, 2013).

In its work, Caniggia establish a distinction between the spatial and temporal relationships,

characterized by the concepts of Copresense and Derivation, respectively (Kropf, 1993) and established

a hierarchy of the urban form, divided into two scales (Building and City), which are subdivided into four

different levels: Elements, Elements of Structures, Systems of Structures and Organizations of Systems.

The urban fabrics are characterized by three entities: the Plot, the Pertinent Strip and the Built route.

Based on the subdivisions of Conzen and Caniggia, K. Kropf establishes a renewed hierarchy of urban

form. This hierarchy use the general definition of the form and the first four levels of Caniggia (Materials,

Structures, Divisions, buildings) and consider the level of Conzen’s plot. The reference point of Kropf

synthesis is the Lot, emphasizing its three-dimensional nature and eliminating the consideration of the

Land Use (Osmond, 2008). In this hierarchy the different elements of the urban form can be identified

in different levels of specificity, increasing the level of resolution of the forms that are to be identified

(Kropf, 1993).

Osmond establishes a system for the Urban Form analysis, linking the updated hierarchy of Karl

Kropf (1993) and the concept of Urban Structural Units, developed by Stephan Friedrich and Duhme

Pauleit (1998). Thus, it creates an updated hierarchy for the analysis of the Urban Form, linking

2 State of the art

2.1 Anglo-Saxon School and M.R.G. Conzen legacy

2.2 Italian school and the system of G. Caniggia

2.3 Hierarchy of Built Form, by K. Kropf

2.4 Paul Osmond and USU´s methodology

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hierarchies of Built Form and Open Spaces, a decomposition of the space through the Space Syntax

method, an inclusion of the urban infrastructure networks and, indirectly, the geophysical properties of

the area. This final hierarchy is the basis for the definition of USU´s and allows you to include the concept

of Surface Sealing, which distinguishes the pervious and impervious surfaces, and the introduction of

the attributes of vegetation. The methodology established by Osmond aims to support the evaluation of

urban form in terms of urban metabolism and Urban Ambience.

The USU´s are homogenous areas regarding to the type, density and arrangement of the urban

form and the open spaces, which defines different configurations of the built environment (Pauleit &

Duhme, 1998). This homogeneity and uniformity of the shape of each unit are the basis for their

distinction. The authors Pauleit and Duhme, Wickop and Böhm (1998) outline the concepts of

"Homogeneity physiognomy" and "uniformity" as relevant characteristics for distinguishing USU’s.

The method of USU´s is applied in the historic center of Évora, classified as World Heritage by

UNESCO and delimited by the medieval wall.

Legend: a – Historic Evolution of Évora

b – Urban Significant Structure of Évora

Figure 1 Évora Historic center maps (1)

Initially we proceed to the study of the historical evolution of Evora (Figure 1, a), in order to identify the

dynamics and organization of the built area, thus allowing the identification of some Built Space units

which characterize the study area, such as the Mourish or the Jewish Quarter. The application of the

method begins with the first division of the study area into two types of spaces: the Open Spaces (parks,

cultivated areas, public space) and the Built Spaces (Figure 2, c). This division begins with the definition

of the Urban Significant Structure of the area (Figure 1, b), which allows you to show the built elements

(white) and the open spaces (black) and thus observe the form of the urban area, in a neutral and

detached form from the architectural and ideological reality way. The Open Space USUs are defined

within the delimited Open Spaces. The procedure is repeated for the Built spaces. The next step is to

3 Application of the USU’s method in Évora

b a

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identify the pervious and impervious surfaces within the city (Figure 2, d). The identification of the

various types of surface provides an important parameter for the differentiation of the USU´s.

Legend:

c – 1st Division: Delimitation of Open and Built Spaces d – Pervious and impervious surfaces

Figure 2 Évora Historic center maps (2)

Figure 3 Final division with Urban Structural Units in Évora

c d

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The consideration of the first division (Figure 2, c) and surface types (Figure 2, d) allows you to make

the final division in USU´s (Figure 3). The Open spaces are divided in four types of USU´s, with different

utilization (Table 1). Similarly eight types of USU´s are selected within the Built Spaces, according to

various Urban Intensities (percentage of built spaces or urban density and number of floors). The

differentiation between the different units is based on the road network (major axis configuration of the

streets and intersections), the configuration of blocks and the percentage of pervious surfaces.

Table 1 Description of each USU´s Type

USU´s Types Description Characteristics Examples

Type 1 Open Space: Vegetation and

cultivation areas Areas with lots of vegetation or cultivation, with few buildings.

Pervious surfaces >80%

Type 2 Open Space: Gardens Walking areas and gardens, with some trees and grass areas. Public garden

Type 3 Open Space: Parking areas Pervious surfaces characterized by white gravel compacted soils. Car parks

Type 4 Open Space: Squares Public quares within the urban fabric. Few trees. Impervious surfaces

essentially characterized by the Portuguese sidewalk. Giraldo Square

Type 5 Low Intensity: Little isolated

buildings > 50% of pervious surfaces.

Type 6 Low Intensity: large isolated

buildings Large isolated or gouped buildings with few storeys. Some trees.> 50%

permeable surface. Primary School

Type 7 Medium Intensity: Little low-rise

buildings Less pervious surfaces (< 50%), located inside of blocks. Residencial

buildings with 1 a 2 storeys. Mourish Quarter

Type 8 Medium Intensity: Large low-rise

buildings Few pervious surfaces (< 50%). Large buildings with 1 a 2 storeys. Arena

Type 9 Medium Intensity: Little hight-

rise buildings Few pervious surfaces (<50%), located within the blocks or private

gardens. Residential buildings with 3 or more storeys.

Type 10 Medium Intensity: Large hight-

rise buildings Few pervious surfaces (< 50%). Large buildings with 3 or more storeys. University, hospital

Type 11 Hight Intensity: Low-rise

buildings Few pervious surfaces (< 10%). Buildings with 1 a 2 storeys. Jewish Quarter

Type 12 Hight Intensity: Hight-rise

buildings Few pervious surfaces (< 10%). Buildings with 3 or more storeys.

Built areas around Giraldo square

Figure 4 Zones chosen for the analysis in Lisbon

4 Urban Sustainability assessment in urban áreas of Lisbon

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This study aims to evaluate and compare the Sustainability of urban areas in Lisbon, with different

tissues and periods of origin, characterizing the different period of urban development in the city. Thus

are chosen Urban Structural Units in seven areas of Lisbon (Figure 4 and Table 2), where are calculated

indicators in order to characterize the energy consumption of buildings in each study zone. In the figure

above, the oldest to most recent selected areas are: Zone 1-Mouraria (Moorish Quarter), Zone 2- Bairro

Alto, Zone 3 – Baixa, Zone 4 – Av. Novas (New Avenues), Zone 5 and 6 – Olivais Sul (South Olivais),

Zone 7- Parque das Nações (Expo).

Table 2 Study areas datas

Zone 1 –

Moorish quarter Zone 2 –

Bairro Alto Zone 3 –

Baixa Zone 4 – New

Avenues Zone 5 – Sth

Olivais, dwellings Zone 6 – Sth

Olivais, towers Zone 7 -

Expo Units

Period of origin XII XVI XVIII XX 1960 1960 1998 -

Area (m2) 72733 41912 60347 140337 64147 31277 86710 m2

Area (ha) 7,27 4,19 6,03 14,03 6,41 3,13 8,67 Ha

Resident Population 2092 961 342 1447 222 755 2466 Inhabitants

N. dwellings 1509 946 467 958 99 300 1082 Dwellings

N. buildings 354 203 92 111 94 12 61 Buildings

The indicators used for the Urban Sustainability assessment (Table 3) are chosen within the set

of parameters of Salat (2011).

Table 3 Indicators results

Indicators Zone 1 –

Moorish quarter Zone 2 – B. Alto

Zone 3 – Baixa

Zone 4 – New Avenues

Zone 5 – Sth Olivais, dwellings

Zone 6 – Sth Olivais, towers

Zone 7 - Expo Units

Utilization Index 2,1 2,5 3,2 2,6 0,3 0,9 2,0 -

% Land Cover 56% 68% 57% 47% 17% 11% 27% %

Average Number of Storeys

3 3 5 5 2 7 8 Storeys

Dwellings Density 207 226 77 68 15 96 125 dwellings/ha

Impervious surface rate

83% 99% 100% 93% 63% 69% 94% %

Proportion of Green Areas

17% 1% 0% 7% 37% 31% 6% %

Intensity of Inersections

4 7 3 1 1 3 3 n./ha

Medium Distance between Intersections

88 42 76 149 319 110 96 m

Fractal Dimensions of streets

0,106 0,325 0,169 0,001 0,361 0,124 0,057 -

Energetic consumption average of Certificates

188 193 195 134 168 130 137 KWh/m2.

year

Energetic Intensity per capita

6791 9524 21256 13340 14957 6180 7187 KWh/hab

Energetic Intensity per surface

195 218 120 138 52 149 204 KWh/m2

Passive Volume rate

44% 36% 55% 33% 65% 54% 33% %

Energy Consumption for heating

80 90 49 56 21 61 84 KWh/m2

Energy Consumption for cooling

35 39 22 25 9 27 37 KWh/m2

Compactness 6,9 5,1 6,8 9,6 9,7 9,1 7,4 -

4.1 Calculation of indicators

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Energy intensity indicators have been obtained through Energy Performance Certificates (EPC),

existing in dwellings of the buildings of each zone. The classification of each energy certificate

corresponds to a percentage range of the reference consumption of the site in the analysis. (Santos,

2010) The consumptions in each zone are calculated by the product of the Average Consumption of

Certificates with the average area of the dwellings (Table 4) and the total number of dwellings (Table

2). The results thus obtained correspond to values of both Energy Intensity indicators. The Energy

Intensity per capita is the division of this result by the number of local residents of each zone and the

Energy Intensity by surface is the division of this result by the total area of each zone.

Table 4 Mean value for areas of dwellings

Zone 1 – Moorish quarter

Zone 2 – B. Alto

Zone 3 – Baixa

Zone 4 – New Avenues

Zone 5 – Sth Olivais, dwellings

Zone 6 – Sth Olivais, towers

Zone 7 - Expo Units

Medium area of dwellings

50 50 80 150 200 120 120 m2/dwelling

The observation of the inicial results allows to identify the most pertinent indicators in order to

analyse the characteristics of each study area and to evaluation the energy consumption of the

buildings. Then, the correlations between each of these indicadors with the Energetic Intensities are

measured (Table 5).

Table 5 Correlations of the indicators wtih Energetic Intensities indicators

Indicators Energetic Intensity per capita (EIc) Energetic Intensity per surface (EIs)

Utilization Index (UI) 0,344 0,464

% Land Cover (LC) 0,246 0,471

Average Number of Storeys (NS) -0,271 0,335

Dwellings Density (DD) -0,551 0,894

Medium Distance between Intersections (DI) 0,256 -0,841

Compactness (C) 0,083 -0,704

Results in red are statistically significant at a 5% significance level while the results in orange is

significant to a level of 10%. The three indicators identified are use in a multivariate analysis (Figure 5).

Figure 5 multivariate analysis

The “Analyse 1” model is significant: 𝐸𝐼𝑠(𝐷𝐷, 𝐷𝐼) = 0,457. (𝐷𝐷) − 0,248. (𝐷𝐼) + 131,673 . Dwelling

Density is the indicator which best explain the energetic consumptions per surface.

4.2 Statistical analysis

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A sensitivity analysis is performed with 31 new study areas, chosen within the initial seven areas in

order to assess the relevance of the statistical analyzes (Table 6 and Figure 6) and the consistency of

homogeneity assumptions of USU´s, made in defining the study areas.

Table 6 Sensibility analysis: correlations

Indicators Energetic Intensity per capita (EIc) Energetic Intensity per surface (EIs) Dwelling Density (DD) -0,224 0,895

Medium Distance between Intersections -0,210 -0,308

Figure 6 Sensibility analysis: multivariate analysis (EIc, to the left, EIs, to the right)

Figure 7 Sensibility analysis: Correlation Eis x DD

Table 7 Average and standart deviation values in each zones

zone Energetic consumption average of Certificates

Energetic Intensity per capita

Energetic Intensity per surface

Dwellings Density Medium Distance between

Intersections

Average Std. Dev.. Average Std. Dev. Average Std. Dev. Average Std. Dev. Average Std. Dev.

1 219 32 8.271 1.470 261 27 245 59 93 11

2 207 17 15.862 10.863 269 83 264 91 44 3

3 221 45 28.033 26.446 112 105 62 53 59 1

4 134 10 14.977 2.739 163 91 81 44 134 21

5 164 42 15.205 3.928 72 24 22 5 155 64

6 130 5 6.318 511 180 103 114 61 120 28

7 126 20 6.910 1.449 194 53 128 23 92 8

The significance of the model obtained for the analysis of Energetic Intensity per surface is increased.

The sensibility analysis confirm the Dwelling Density as the most relevant indicator in the energetic

consumptions assessment. This analysis also allows to assess the homogeneity of USU´s selected in

Lisbon. In this case, the Zone 2 and 3 present the lower level of homogeneity, while the Zone 5 present

the highter level.

0

100

200

300

400

0 100 200 300 400

Ener

geti

c In

ten

sity

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rfac

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Is)

Dwelling Density (DD)

EIs x DD - Sensibility analysis

Zone 1Zone 2Zone 3Zone 4Zone 5Zone 6Zone 7

4.2.1 Sensibility analysis

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The USU´s methodology offers several maps for the study area: a map of Urban Ecology,

illustrating the vegetation structure, a map of the built areas and the open spaces and, a map of USUs

which allows to assess the organization of the city and the Urban Metabolism. These maps can

complement traditional municipal plans, as the Land Use map. 197 USUs have been identified, divided

into 12 types. The historic center of Évora is thus characterized by built-up areas of small buildings with

few floors, with few pervious surfaces, located largely in private spaces inside the blocks. This method

reveal some sustainable characteristics of the study area, such as a compact urban area constituted by

a built fabric quite diverse and complex. The high complexity of of Évora, caused by several changes

and adaptations of the city over the centuries, reveals the resilient feature of the city. The Urban

Intensities associated to each type of USUs enables analyzing the urban metabolism, that is, the various

flows existing in the city. This Metabolism reveals the important role of Giraldo and Sertório Squares

and the main streets linked to these spaces. The observation of Urban Metabolism can be deepened

by quantifying certain indicators, within the identified units.

The oldest areas of Lisbon have higher values of Utilisation Index and Land Cover Percentage.

The observation of the results shows that the old quarters with traditional forms have higher densities

and compacity, compared with modern areas, with lower buildings. The increase in urban density is thus

not achieved through buildings with many floors but may become possible through traditional blocks

with an average number of floors.

The Energetic Intensity by surface have more significant results with the Dwelling Density, the medium

Distance between Intersections and the Compactness These three indicators are then used in a

multivariate analysis, in order to obtain a model able to analyze and explain the Energetic Intensity by

surface. The significant results of the multivariate analysis corresponds to the analysis of Energetic

Intensity per surface with the Dwelling Density and the medium Distance between Intersections. This

model shows a good correlation (R = 0.931) and can explain 86.7% (R2 = 0.867) of Energetic intensity

per surface: 𝐸𝐼𝑠(𝐷𝐷, 𝐷𝐼) = 0,457. (𝐷𝐷) − 0,248. (𝐷𝐼) + 131,673. Dwelling Density is the indicator that

best explains the Energy Intensity by surface in the several analysis. The analyzis reveal that an

increase of urban density is related to a reduction of consumption per surface. The compact traditional

Blocks have less energy loss through their facades and are characterized by a lower Energetic Intensity

per surface, thus confirming the results of Serge Salat work, although the result of Compactness, in the

multivariate analysis model was not statistically significant. The sensitivity analysis repeated the

statistical analysis by replacing the initial seven study zones in thirty-one smaller units. This analysis

allowed to determine the relevance of the statistical results and homogeneity assumptions of USU´s

used in the Urban Sustainability assessment in this work.

The calculation of some indicators used in the analysis of Urban Sustainability revealed some

limitations. Demographic data refer only to the values of the resident population and residential

5 Discussion of results

5.1 Analysis of urban form in Évora

5.2 Urban Sustainability assessment in Lisbon

5.2.1 Limitations of the analysis

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dwellings, thus excluding the values of other activities (commercial, offices and services). So there are

errors in the results of some indicators that generate inequalities in the comparison between the different

study areas. These errors were mainly observed in the calculation and the statistical analysis of the

Energetic intensity per capita, which is very inconsistent, particularly in the Zones 3 and 4, and have a

low level of significance, in a statistical way. Both Energetic Intensities were calculated using the values

of Energy Performance Certificates (EPC), related only to residential dwellings. The Energetic

Intensities used in this work does not correspond to the total consumption in selected areas because

they do not consider the consumption due to other existing activities in buildings or other consumptions

(transports, street lighting…), and assign a greater weight of the active part of the energy efficiency of

dwellings, derived from the calculation of energy efficiency certificates mentioned above (Ferreira &

Pinheiro, 2011). The values of the Passive Volume rate can contribute to the analysis of the passive

part of energy consumption but shown a lack of precision and consistency. However, this analysis could

be performed through correlation with other indicators, such as the percentage of glazing and the level

of shading of the buildings considered.

The application of USU´s methodology in the historic center of Évora revealed a built form,

compact and complex, as several sustainable features. The method allows you to analyse, in a

qualitative way, the Urban Metabolism of the area.

The analyzis revealed a higher correlation with the Energetic Intensity per surface, which is best

characterized by the Dwelling Density. The Medium distance between Intersections and the

Compactness have also good correlation, although not statistically significant.

This thesis presents a coherent and practical methodology for assessing the Sustainability of urban

areas with different fabrics and periods of origin. The methodology shows the possible relationships

between the analysis of Urban Morphology and Sustainability. The Observation of the traditional forms

of cities shows tissue adapted to the respective terrains and climates and, in this way, their study may

be particularly relevant to the understanding of urban sustainability.

There is a possibility of using different types of urban tissues identified in this work as part of a library

or inventory of existing forms, as suggested by Professor Karl Kropf during the ISUF conference in June

2014 in Porto. The methodology established in this study can identify many of these types of tissue and

connect each of them to average energy consumption.

Ferreira, J., & Pinheiro, M. (2011). In search of better energy performance in the Portuguese buildings-The case of the Portuguese regulation. Energy Policy, 39(12), 7666–7683. Retrieved from http://dx.doi.org/10.1016/j.enpol.2011.08.062

Kropf, K. S. (1993). An enquiry into THE DEFINITION OF BUILT FORM IN URBAN MORPHOLOGY - volume one and volume two. PhD thesis, Department of Geography, Faculty of Arts, University of Birmingham.

Moudon, A. V. (1997). Urban morphology as an emerging interdisciplinary field. Urban Morphology, 1, pp. 3–10.

6 Conclusions

References

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Salat, S. (2011). LES VILLES ET LES FORMES : SUR L’URBANISME DURABLE (Hermann). CSTB - Laboratoire des Morphologies Urbaines.

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