ATHENS in-between and on-the-top / AA SED

AA.E+E.Environment.&.Energy.Studies.Programme Architectural Association School of Architecture / Graduate School MSc.&.MArch.Sustainable.Environmental.Design.2012-­13 T

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A . T . H . E . N . S . : . i n -­ b e t w e e n . a n d . o n -­ t h e -­ t o p A n a s t a s i a . G r a v a n i . / . J a n u a r y . 2 0 1 3

ABSTRACT Urban retrofitting has to deal with the complexity of the city and its components. As long as their potential is totally understood and transformed into architectural knowledge, understood they will consist catalytic tools for sustainable regeneration strategies. Through this research an analysis of the dense urban structure will offer fundamental information about its form. Moreover the environmental aspects that need to be considered will be revealed.

Taking Taking Athens as a case study, this essay intends to explore deeper the environmental potential that emerges into the components of the urban tissue. The studies have been based on four dissertation projects conducted on the subject over the course of the past decade. Finally, evaluation of both assessed and proposed strategies will lead to a principal conclusion of the issue.

TABLE OF CONTENTS

INTRODUCTION

PART A: CONTEXT / ENVIRONMENTAL PERFORMANCE OF URBAN AREAS

1_HIGH DENSITY URBAN ENVIRONMENTS Impact on the environmental performance 2_URBAN HEAT ISLAND (boundary layer / canopy layer) Parameters that affect the intensity of the phenomenon 3_ CHARACTERISTICS of the URBAN GEOMETRY AFFECTING THE URBAN HEAT ISLAND EFFECT What are the chances to mitigate the UHI?

PART B: CASE STUDY / ATHENS: IN BETWEEN AND ON THE TOP

4_ATHENS _climatic conditions _special urban geometry characteristics

_leftover spaces that emerge: “In between” space “On the top” space

5_ANALYSIS METHODS: “In between” space “On the top” space

6_OUTCOMES

CONCLUSIONS REFERENCES

INTRODUCTION Architecture nowadays, apart from designing new worlds, has to confront the world that is already designed and moreover the subjects that were inevitably created within and by it. During this process of dealing with the existent structure, urban refurbishment has always provided significant importance to transitions, to remains and significant leftovers, to discontinuities and to differences (to the dT, or range over time) as this is where every “potential” to change or to become is lodged.

Moving Moving to the Athenian scene, the dense built environment determines these catalytic spaces in direct correlation with its existence. Every “potential” to change or to become is located IN BETWEEN AND ON THE TOP of the city’s fabric.

This This paper intends to evaluate the potential of these areas that exist above and around the structures and envelopes which capture the architecturally designed space, seeking to identify possible future environmental states of the urban system. To achieve so, an approach to the basic characteristics of the urban structure will be held, providing useful evidence for their possible impact on the environmental performance of the system. A short environmental approach to the principle causes of the heat island effect will be presented, in order to identify possible strategies for its mitigation.

Considering Considering Athens as a case study, literature sources and researches will establish the layout of proposed strategies that could be applied to the leftovers of the urban structure, aiming to reform the microclimate conditions. Conclusions will be derived about the potential role that something as seemingly omnipresent, inert and dependent as in-­between and on-­the-­top space can play in the formation of the urban microclimate.

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PART A: CONTEXT / ENVIRONMENTAL PERFORMANCE OF URBAN AREAS

1_HIGH DENSITY URBAN ENVIRONMENTS Impact on the environmental performance Contemporary human needs have always come to control the way that space is used, leading to the gradual creation of dense urban environments. Several questions emerge about the impact of the urban expansion rate -­either criticized as too intense, either as not intense enough-­ on the environmental performance of the urban space.

As Givoni states (1989,pp1-­2), “the climatic conditions in a man-­made, urban environment may differ As appreciably from those in the surrounding natural or rural environs… each urban man-­made element creates around and above it a modified climate with which it interacts”.

Simultaneously with the urban growth during the last centuries, the effort to clarify this modified climatic conditions that occur around and above the urban structure has been intensified. As a result, the increased air and surface temperature has been observed in several urban and suburban areas, leading to the first documentation of the Urban Heat Island effect in 1818, when Luke Howard’s referred to “an artificial excess of heat” in documentation the city of London compared with the country (Gartland, 2008, pp1).

2_URBAN HEAT ISLAND (boundary layer / canopy layer) Parameters that affect the intensity of the phenomenon The basic characteristics that exhibit the heat islands are: the increase of air and surface temperatures, the intensification of the effect during clear and calm weather, the parallel growth with the expansion of the city, as well as intensification the phenomenon of air temperature inversions over cities. According to L.Gartland (2008, pp 15), these characteristics can be sorted into the five main causes of heat island formation: reduced evaporation and convection, as well as increased heat storage, net radiation and anthropogenic heat.

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As far as the scales of the city are concerned, the urban heat island affects not only the surfaces of the built environment, but also the space located in between and above the city. These parameters determine the basic distinction between the surface (SHI) and the atmospheric heat island effect. The latter can be identified in the area distinction upwards to the average building height, or in the space above the built environment, forming respectively the sub-­division into the canopy (CLHI) and boundary (BLHI) layer heat island effect.

Their intensity varies at each location of the city, equilibrating between surrounding temperatures and released energy.

Apart from the climatic conditions and the anthropogenic heat, the phenomenon is also affected by the geometry and materiality of the urban form.

As As M. Kapsali suggests, there are several parameters in the geometry of the urban canyon that play a major role in the energy balance equation. The absorption of short wave radiation is increased by the multiple surface reflections, while the sky view factor (SVF) decrease leads to less loss of long wave radiation. Moreover, the decrease in wind speed, in between the built areas, causes decrease in heat dissipation through turbulence. As for the urban morphology, the height to width ratio (H/W) as well as the orientation of the urban canyons or the free spaces affects the amount of solar radiation absorbed and reflected by the urban structure. Last but not least, materiality of the external surfaces of solar the built environment affects dramatically the heat island formation. This happens because most of the urban materials are impermeable and watertight, with low moisture levels, not being able to dissipate the sun’s heat. Additionally, their dark colors contribute to the increased collection and trapping of the energy of the sun.

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fig.02 urban density / Athens

fig.03 case studies / Athens

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fig.04 free spaces / Athens

PART B: CASE STUDY / ATHENS: IN BETWEEN AND ON THE TOP

4_ATHENS _climatic conditions Athens is the capital of Greece, located in the southern part of Europe, at a 37.9°N Latitude and 23.7°E Longitude, while the average elevation is 45m above sea level. The contemporary city extends across the central plain of Attica basin, surrounded by four mountains: Parnitha, Penteli, Aegaleo and Hymettus and enclosed by the Saronic gulf on its southwest border. The city is characterized by long dry and hot summers and mild winters, typical aspects of southwest Mediterranean areas. The climatic conditions throughout the urban fabric of Athens are quite complex, being influenced not only by its rich topography but also by the high density urban structure that has been formed mainly during the last centuries.

Large scale experiments elaborated in Athens in 1996 verified the existence of an intense Urban Heat Island Large (Santamouris et al, 2001) with an average temperature difference of 7-­8K during summer months, reaching a peak of 12-­13K in high-­traffic canyons. Although at night there was a drop to 3K difference between the urban and suburban areas, the phenomenon still occurred. The increased temperature levels leads to higher energy demands and downgrade the quality of human comfort. All the above, alongside with the increased air pollution levels, highlight the downgrade crucial need to mitigate the urban heat island. In order to achieve so, studies have been focused on the special urban geometry of Athens, trying to identify the possible implementation that could affect the environmental microclimate of the city.

_special urban geometry characteristics Regarding the contemporary urban tissue of Athens, without analyzing the social and economical factors that dictated its formation, it is characterized by high density areas around the center with mixed uses organized on the vertical axis.

That means that the public uses are located on the ground and first floor level, while the rest of the built volume is commonly used to cover residential or office needs. This distribution of the uses, combined with the Greek building regulations, developed a quite homogeneous urban tissue, consisting of buildings with similar characteristics and spatial principles.

Another significant aspect of the Greek capital is the lack of open spaces. It is worth mentioning that total green areas (m²) to number of residents ratio was significantly low for Athens in 2006, reaching only a value of 2.55. At the same time, in other European countries the values were dramatically higher going up to 9 for London, 27 for Amsterdam and 13 for Berlin (Source:http://www.minenv.gr/).

The basic component of the Athenian layout is the urban block, as a result from the system of continuous building, according to which the buildings must be aligned to the front and side boundaries of the plot (GBC 1957-­1985). The according prevailing geometrical configurations of the urban block are mainly two, the square and the rectangle. The blocks are typically oriented N-­S and E-­W with deviation of up to 30ĥ in either location (Yannas and Baker, 1983). This is the urban unit that most of the researchers take into account during their studies on the city of Athens.

Square shaped block side dimensions vary from 40m to 50m. The void’s side dimensions vary from 15m to 20m. The size of the rectangular blocks is approximately 40-­50m by 80-­100 m and the dimensions of the void are 10-­20 m by 50-­80m (Vogiatzi-­Tamba, rectangular 2009). The height of the residential buildings generally varies between 5 to 7 storeys, resulting into 15m to 21m high. Setbacks are a very common case, and are usually found at the top one or two floors. In the case of the rectangular urban void, these dimensions correspond to a H/W ratio between 0.2 and 0.4 along its long axis, while in the case of the square shaped urban void the H/W ratio is around 0.75 reaching 2 in some cases. The percentage of void and roof with respect to the plot depends on the dimensions of the block and the void. The rectangular shaped block can have a void percentage of 10% to 25% of the plot area, while the percentage block of the square shaped block varies between 9% and 16% (Vlachou, 2011).

fig.05 circulation net and green areas / Athens

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strefis.hill

pedion tou areos park

The configuration and repetition of the urban blocks within the urban tissue have been assessed and further evaluated several times, so as to determine the potential for a sustainable regeneration. As far as the heat island effect is concerned, it is worth mentioning that the majority of the studies focuses on the potential retrofitting by taking advantage of the space created around and above the urban blocks.

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_leftover spaces that emerge: “In between” space The general building code dictated the formation of a continuous street frontage alignment around the perimeter of every block (GBC 1957-­1985). However, these restricted urban units are not totally compact. The restriction of a minimum uncovered area equal to 30% of the plotted surface was the main cause of the constitution of the urban voids, which are commonly placed inside the urban blocks. The fragmented ownership as well as the restricted access are recognized as the main factors preventing their integration to the urban net.

These non-­designed spaces consist the typical yards of Athens, presenting a variety of microclimatic conditions that affects -­and is affected by-­ the built environment. This bidirectional relationship verifies the potential for a sustainable regeneration through environmental retrofitting of the space located in between the urban construction.

M.Kapsali, H. Vlahos and A.Vogiatzi-­Tampa aimed to analyze and evaluate this potential, by studying different samples M.Kapsali, within the urban tissue of Athens. As a first step analysis of the contemporary environmental performance of these spaces was made. Moreover proposals were suggested, with a re-­evaluation of the proposed case conditions, in order to derive some guideline conclusions about their contribution to the urban refurbishment.

“On the top” space Apart from the space deteriorated between the built areas, on the top of the Athenian urban construction, a unique horizontal layer of free space has been created. Roofscape has never been taken into account as the “fifth elevation” of horizontal the buildings. On the contrary, it remained as an unused, fragmented space resulting by the gradual development of the buildings that consist every urban block.

In order to allow the maximum sun penetration at street level, the upper part of the front facades of the buildings are in scaled formation, while the back yard facade is vertically extended. “Antennas and auxiliary volumes housing the endpoint of elevators and stair¬cases punctuate the roof area and ultimately shape the roof level skyline” (H.Vlahos, 2011).

The The use of flat roofs once made technically possible by waterproofing and the invention of concrete, was praised by architects since the beginning of the 20th century, reaching its summit with the modern movement (Martinez, 2005).

However, in the Greek context, rooftops never managed to be functional spaces, even after the gradual revisions of the general building regulation during the past decades.

Several Several efforts for the sustainable reactivation of the urban roofscape of Athens have been conducted. Through their studies, M.Kapsali , K.Pantazi and H.Vlahos observed that in an urban environment characterized by high density and absence of green areas, the leftover spaces described above have a high potential in terms of sustainable regeneration, without demanding big scale urban planning.

Parallel Parallel to the separated proposals for either the urban voids or the roofscape of the city of Athens, the combination of both strategies has also been promoted by the revision of the building regulation that occurred in 1985 (ΓΟΚ Ν. 1577-­ 1985), giving the opportunity to merge these spaces into common used areas for the occupants of the urban blocks.

Despite the fact that this option has not been actually implemented in general, M.Kapsali and H.Vlahos studied the possible environmental aspect of a combination of strategies applied in between and on the top of the urban fabric.

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5_ANALYSIS METHODS: The four mentioned researches verified the environmental potential of leftover spaces in order to mitigate the urban heat island effect that occurs in Athens, in both the canopy and boundary layer. To further evaluate the proposed interventions and their outcomes, the analysis methods were initially compared.

In all cases, after the investigation of the urban framework and the theoretical background, general conclusions are presented about environmental concerns in urban case studies. Furthermore, an approach of the urban context of presented Athens is made, identifying its special features. The second part of the studies is subdivided into the analytic work and fieldwork, which vary in each case.

“In between” space The The first study deals with the subject of “Refurbishing the Urban Blocks in Central Athens” (M.Kapsali, 2012). During the fieldwork the microclimatic conditions in a specific urban environment are being analyzed, taking a wide urban area in the neighborhood of Kypseli as a case study. Measurements are taken in the whole area, on the pedestrian level, as well as within urban voids with different materiality. Analytic work based on simulation models focuses on four principal parameters that affect the microclimate in an urban scale. More specifically, the examined parameters are: geometry, materiality, anthropogenic heat and vegetation.

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The next study is titled: “Leftovers. Exploring the Environmental Potential of Roofs and Urban Voids in Athens” The (H. Vlahos, 2011). As far as the “in between” spaces are concerned, fieldwork takes place in two different urban voids in Athens, which differ in terms of materiality. The first is a planted urban void, whereas the second is a mineral urban void. Both areas are located in the city center of Athens, within a distance of 1km. Having the results of the two case studies as feedback, in the part of analytic studies the impact of a single parameter is explored in both block and urban scale. The parameter of study for this comparative analysis is materiality.

The aim of the third study was to explore possible ways of “transforming the Urban Void to an Urban Scene” The (A.Vogiatzi -­Tampa, 2009 ). During this effort, analytic work and fieldwork are seen as parallel processes. Fieldwork is not based on specific case studies. Simulations of typical urban blocks are run instead, taking into account the main parameters of differentiation which are geometry and orientation. Since the different case studies are determined through these simulation models, further evaluation of the parameters of openings in the building mass and materiality is assessed. Finally, measurements are taken from five blocks in the city center, in order to evaluate the simulation results and to provide evidence for the design proposal.

“On the top” space As already described, M. Kapsali examined in her study (“Refurbishing the Urban Blocks in Central Athens”, 2012) the potential of the environmental retrofitting of the urban block, focusing on the refurbishment strategies applied on the ground level. However, the effect of possible interventions on the roof tops is also highlighted, in terms of materiality and green areas .The results presented refer to the implementation of refurbishment strategies at a small or a bigger scale.

Furthermore, Furthermore, “Urban Metaphors” (K. Pantazi, 2010) is a research focused on the Athenian roofscape. Analytic work can be divided into two parts, starting with the simulation of the typical urban blocks of Athens, in order to derive initial conclusions for their environmental potential. As a step further, the monitoring of two case studies in Athens, in the area of Pagkrati and Exarheia, offers the opportunity of better understanding the urban roofscape. Moreover, during fieldwork studies, a further assessment of microclimatic configurations took place for the case study in Pagkrati. The results have been employed as a tool to propose environmental strategies for this particular urban rooftop. results Finally, in H.Vlahos’ research for the environmental potential of the urban roofs, the whole process of fieldwork is structured parallel to the urban void analysis that has been already described, analyzing two case studies that vary in structured terms of materiality. The first examined rooftop case is a planted roof, while the second is a mineral one. Analytic work is based on the comparative analysis of the case studies. The main concern is the evaluation of different materiality when it is implemented only in one urban block, as well as its expansion potentials at a wider urban scale. The latter is studied through simulation runs.

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