Dissertation - Building Skin and Shading Devices

-adaptive faรงade_Al Bahar tower, Abu Dhabi

Building Skin and Shading devices

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Acknowledgement

I thank God

I’d like to thank all of my friends and family who have contributed in any way towards the completion of this dissertation, especially my guide Prof. Ayyapan K.A and my advisor Prof. Poornima Kurup for their guidance and support. I am also grateful to the faculty of TKMCE – Mrs Sheena and Mr Shafeeq. I would also like to thank the H.O.D of the dept. of Architecture – Dr. Annie John.

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Abstract The turn of the 21st century has brought with it a new wave of architecture in India.

However adaptations from the colder climates often ended up raking huge energy costs for maintaining thermal comfort inside building envelops with expansive glass facades. In many cases vernacular architecture was replaced by less sustainable methods. In this scenario, the concept of a secondary skin around the traditional building envelop is a revolutionary idea that helps find the balance between functionality, aesthetics and sustainability.

Once when brick and concrete facades was the preferred architectural vocabulary, there were few ways to incorporate climatic control into the design except by means of mechanical heating and cooling. The embodied energy of the materials used to construct these structures are too high when we think about the technology we have at our disposal right now. Multilayered faรงade systems and improved material qualities allow much better resource utilization and performance enhancements compared to their predecessors. The versatility of building skins constructed with these enhanced materials is demonstrated through its varying use around the globe for controlling various climatic and other parameters. Modern building skins and faรงade treatments take advantage of cellular geometry and advanced material engineering to create lighter structures that have begun to define a new kind of architecture.

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Aim The aim of this dissertation is to elaborate the different aspects of building skin design and study current examples that pioneer in sustainable and climatic performance in order to arrive at guidelines for designing a proper envelop for the tropical climate.

Objectives 

Study the different typologies of building skins and shading devices.

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Analyze their materials, construction techniques and climatic performance.

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Analyze how building skins and shading devices can be employed for the design of conglomerate and residential buildings.

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Explore how building skins can be integrated into the current architectural vocabulary of sub-tropical climates.

Scope and limitations This dissertation explores how building skins and shading devices can be employed for the design of conglomerate and residential buildings. Also studying and citing different examples in order to arrive at guidelines for climatic performance in Kerala. The scope of this dissertation however is limited to building skins and their materials, their ecological responsiveness and their applications only. Structural Analyses of such structures and materials are beyond the scope of this dissertation.

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Methodology

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Contents Acknowledgement ............................................................................................................... 2 Abstract ................................................................................................................................ 3 Aim ...................................................................................................................................... 4 Objectives ............................................................................................................................ 4 Scope and limitations ........................................................................................................... 4 Methodology ........................................................................................................................ 5

1.1 Shell – Skin – Façade ..................................................................................................... 8 1.2 Origin and evolution ...................................................................................................... 9 1.3 Functions and classification ......................................................................................... 14 Comfort factors as parameters for building skin design ............................................................ 15 Energy-related parameters of the building skin ................................................................ 17 The impact of facade and roof design on energy consumption ................................................ 18

2. Perforated building skins in the Mediterranean and the Indian subcontinent ................ 23 2.1 Types of traditional perforations .................................................................................. 25 2.2 Daylight performance of Jaali Screens. ....................................................................... 29 Solid void relationship................................................................................................................ 30 Overhang ratio ........................................................................................................................... 30 Jaali glare renderings ................................................................................................................. 33 why it matters ............................................................................................................................ 33

3. The modern take on perforated screens – Park Hotel, Hyderabad................................ 35 Climate in Hyderabad ................................................................................................................ 36 The Façade ................................................................................................................................. 38 Project credits ............................................................................................................................ 42

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4. The new Mashrabiya – Al Bahr towers, Abu Dhabi ..................................................... 43 Performance ............................................................................................................................... 45 Materials..................................................................................................................................... 46 Façade......................................................................................................................................... 47 Design process and testing ......................................................................................................... 48 Benefits of the shading system .................................................................................................. 50 Project credits............................................................................................................................. 51

5. The Future – A Real Skin .............................................................................................. 52 Hygromorphically responsive Skin ............................................................................................. 53 Bloom – Doris Kim Sung ............................................................................................................. 56

6. Designing building skins for the tropical climate. ......................................................... 59 Building Orientation ................................................................................................................... 60 Perimeter to area ratio ............................................................................................................... 62 Shading strategies for windows and openings ........................................................................... 62 Retrofitting ................................................................................................................................. 64 Variable Solar Protection Glass .................................................................................................. 66 Breathable glass façade .............................................................................................................. 68

7. Conclusion ..................................................................................................................... 70

8. References ...................................................................................................................... 71

9. List of figures ................................................................................................................. 74

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1.1 Shell – Skin – Façade As a transition between inside and outside - between the house and the urban space - the building skin plays an especially important role. First and foremost it provides protection from the elements, demarcates private property and creates privacy. But its aesthetic and cultural function is just as important. The building skin - and especially the facade - is the calling card of a house and its designer. Set into context, it characterizes the face of a city.

No wonder that it draws more attention than any other building component. The ideas established by Modernism - which continues to exert its influence today - stipulate that the external appearance of a building should reflect its internal life. Harmony should reign between form and function, inside and outside. Recently, this demand has been questioned with growing intensity. For as the building skin was separated from the load-bearing structure, it became a curtain, pure skin. To begin with this was expressed in the smooth, frequently sterile curtain walls, which defined our urban environments for so long. Most recently, however, the surface - and hence its material - has become the central focus of investigation. ( Christian Schittich, Building Skins. Germany: Birkhauser, 2001) The building skin or shell is essentially the envelope that segregates the spaces inside the building from the spaces outside. The façade is essentially ornamental packaging that defines aesthetics and gives character to the building. It used to be more associated with identity It isn't always easy to draw the line between a useful skin and ornamental packaging. It is fascinating to observe how vastly different the reactions of individual architects are to this particular aspect. Some adapt to these new perceptions and react with equally colourful, serigraphed images on brittle glass. Or with flickering media facades and illuminated screens. Others, however, look back to the quality of ancient building materials - massive natural stone or exposed concrete, untreated timber and brick masonry, to demonstrate the solid physical presence of a building in an increasingly virtual world.

Between these extremes, lies a third, equally contemporary path: the building skin as a responsive skin, as one component of a sustainable low-energy concept. This begins with simple Jaalis or folding and sliding shutters or with the popular moveable louvres and culminates in multi-layered glass facades equipped with a multitude of devices for shading and glare protection, light deflection, heat- and energy gain. Today, in the face of 8

diminishing raw materials and growing C02 emissions, this approach is increasingly important. It seems to offer the best of both worlds: contemporary facade design without running the risk of superficial ornamentation or the risk of material fetish. Given all these possibilities, the topic of "building skins" is as fascinating today as it has rarely been in the history of architecture. Wherever we look, we encounter unbounded joy in experimentation: testing boundaries, querying traditional perceptions, searching for new materials and concepts.

1.2 Origin and evolution Man builds a house as shelter from the elements, wind and rain, cold or excessive heat. He wants to draw a line around his property, create his own private sphere. But what came first: the roof or the wall? To pose this old question is as futile as the story of the chicken or the egg. But it contains the question whether the building skin served primarily as a ceiling enclosure to provide weather protection or as a lateral enclosure to keep roaming wild animals at bay. This debate originated mostly with Gottfried Semper, who held that the animal pen, a fence woven from branches and twigs, was the origin of the wall, and hence of architectural space. In his seminal work "The Style" in the mid 19th century, Semper refers to the common origin of cladding and spatial art. Semper divides architecture into load-bearing structure and cladding - a theory that would have a far-reaching influence on Modernism, which is as pertinent today as it was then.

A more developed, but equally ancient form of construction in the Semperian sense are the round tents of some nomadic tribes, such as the Jurts among the Turkish tribes or the ancient Mongolian tribes. Since time immemorial, however, people have also erected load-bearing external walls. The determining factor in the evolution of different building methods was the availability of local building materials, as well as the lifestyle in response to the local environment.

At first building skins were entirely oriented towards fulfilling specific functions. It didn't take long, however, before people began to decorate the building skin as lovingly as they did their own clothing. To begin with this applied to simple homes, and especially to the monuments of different eras and cultures, equally true for elaborately frescoed Greek and 9

Chinese temples or Islamic palaces and mosques. The works in stone and Marble Jaalis in the Indian temples and the incredibly detailed workmanship found in the Mashrabiyas of Mausoleums were the leading examples of this time. On the other hand, european antiquity transformed the faรงade into a unique showcase with which public buildings presented themselves to the urban space. In the Renaissance, especially, facades began to separate from the house; that is, they are placed in front of an old church or palace as a new "cloak".

They fulfil a primarily aesthetic purpose: attractive packaging. The design of facades in the classic sense, their proportion, fenestration, division by means of architraves, columns and rusticated ashlar stones, has been the main focus of architecture for many centuries in addition to interior design.

The increasing opening of the external wall, the relation of window to wall - of open and closed surface is one of the principle themes of the external skin. To begin with, it would seem, our ancestors had a true love of the dark, the mystic. Small openings in the wall were not only determined by construction methods in many traditional building styles - for in principle it is difficult to puncture the wall with large window openings in a massive stoneor sunbaked clay structure - but also out of a desire for protection and shelter. Man yearns for his cave. Moreover, in times when glass was still a rarity, openings were the primary source of energy loss, and this alone dictated that they should be as small as possible. As architecture was increasingly liberated from the constraints of the load-bearing wall, coupled with advances in glass manufacture and technology, appreciation for light in interior spaces increased as well. The original, instinctual preference for secretive, dark spaces gradually gave way to a desire for illumination.

Sacral buildings in the Gothic demonstrate the first attempts to create generous openings in the stone-faced shells. The formerly compact volumes of cathedrals and churches are dissolved into a skeleton of load-bearing and supporting elements that are almost entirely orientated towards load distribution (in keeping with the principal building material stone).

The building skin evolves into a structure composed of ribs and vaults, masonry surfaces, flying buttresses and pillars. Large sections of the external wall are liberated from their load-bearing function and freed for the insertion of huge windows covered in tracery: architectural space opens towards the light. Translucent, coloured glass which allow light to penetrate but obscure vision become filters between inside and outside, but also giant image carriers lit from behind.

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But in housing windows would remain small for a long time to come (with the exception of the early bands of windows in framework construction, where larger openings are possible by linking many smaller formats due to the post-and-beam structure). Their existential significance as a link between inside and outside is expressed in the attentive treatment and special emphasis with coloured or structural frames. From the Middle Ages onwards, most windows are glazed, although the material remains a luxury until the Industrial Age. Hence, the glazed areas were still moderate in size.

The traditional window is rarely a plain hole in the wall. It is nearly always one component in a spatially layered transitional zone. Curtains, blinds, folding shutters, window sills and flower boxes each fulfil a different task and create a "gentle" threshold from the outside to the interior.

This threshold was treated in a unique manner in the traditional Japanese house. Large sections of the external wall consist of paper-faced, light-permeable sliding doors with timber frames. When opened, they create a fluid transition from the garden into the living space. Wide roof edges and a veranda around the entire periphery of the house enlarge this transitional zone. Solid sliding shutters, attached to the outside of roof and veranda, create a flexible double-layered skin that offers a measure of protection against cold even in winter; in the summer months, textiles and bamboo shades suspended in front of the facade protect against the searing sun. The flexible external skin of the Japanese house is capable of responding to a wide range of situations and allows for a varied relationship between inside and outside.

In the 19th century, the Industrial Revolution changed the world. New materials and production methods opened up entirely new opportunities - iron and glass conquered architecture. The process of dissolving the building skin - its, de-materialization - is directly linked to the progressive independence from its load-bearing function. Important impulses are provided by the builders of greenhouses, by gardeners and engineers. The history of the greenhouse is an important chapter in the history of European architecture, even though many were created without the participation of architects. The pioneers of glass- and iron architecture, John Claudius Loudon, for example, or Joseph Paxton, designed their daring structures primarily in accordance with purely functional aspects. To achieve a maximum amount of incident sunlight, they try to reduce the massive wall components to a minimum.

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Ornamentation, a common feature in the architecture of their day, is almost entirely absent in these structures. Often they utilize the glass panes to provide the necessary bracing for the construction, which leads to a filigree structure. Thus in the palm house, which the brothers Bailey erected circa 1830, probably with the help of Loudon, in Bicton Gardens in Devon, England , The bent glass skin is very much like a membrane in this building. The highlight of transparent buildings was no doubt Paxton's Crystal Palace, constructed for the World's Fair in London in 1851. Every aspect of this ground-breaking structure was developed in accordance with the requirements of the task, the conditions imposed by scale and span, the costs, prefabrication and assembly times. Only a "non-architect" like Paxton could be as innocent in his design for this particular task. Only a gardener, as he was, could so casually negate the formal canon. London's Crystal Palace fascinated everyone in Europe and precipitated a trend for glass exhibition buildings in other cities. Other building tasks, too, were soon after realized in transparent structures composed of iron and glass, such as train station terminals or large shopping arcades. Once again many of the daring even visionary designs were created by engineers and non-architects, while the architects themselves seemed content with decorating facades and entrance structures with traditional styles, ignoring the changes that had overtaken them.

Functional and commercial demands influenced the increasing openness in urban facades.

In the middle of the 19th century, the first tall buildings with iron load-bearing structures were erected in the United States at a time when open interior spaces, supported only by piers, were very much in vogue. Skeleton construction made it possible to simultaneously open up the external walls with large windows in metal frames. To begin with, this approach is predominantly chosen for warehouses, factories and other purpose buildings, where architecture doesn't play such an important role. The development of the necessary building technology (steel skeleton construction and elevators), led to the creation of the first high-rises. But the traditional massive external walls proved to be uneconomical and also offered few opportunities for advantageous lighting. The logical next step was to use iron and glass in ever more generous expanses on the facades of the new representative office buildings. The growing independence of the external skin from its structural function leads of necessity to its complete separation from the load-bearing structure. The roots of this developed are found in the Chicago of the 19th century, even though the facades of its early high-rises are still realized on the level of load-bearing structures, that is, the glazing 12

is set into fields delimited by the floor slabs and the pillars. Similar to, the early metal facades in the United States, the first skins that are fully freed from the load-bearing structure (later called curtain wall) were realized in industrial buildings created without any obvious participation of architects. Once again, function drives the agenda: to achieve a maximum of light, the external walls are glazed as much as possible. One of the earliest examples is the east facade of the Margarethe Steiff factory building in Giengen in southern Germany - a project that was most likely initiated by Richard Steiff, the grandson of the company founder. The external layer of the double-layered facade composed of translucent glass panels is suspended in front of the structure and stretches across three storeys and around the corners as a smooth skin, divided into even sections. The internal skin lies between the supporting pillars.

Until the early 1970s, glass curtain wall buildings spread around the world under the influence of the International Style with unprecedented speed. The office building has become an important building task and the glass facade with its grid has become its primary symbol. Moreover, the smooth, uniform curtain wall is promoted by the proliferation of anonymous investment architecture. Facade creations that began as creative, elegant solutions degenerate into monotonous surfaces. Climatic parameters were ignored and soon the image of the glass faรงade in the west was starting to be imitated without much adjustment to tropical countries such as in the Indian subcontinent.

From the mid-sixties onwards, the new method of fixing external glazing by means of loadbearing silicon (structural sealant glazing) and other innovative fixing techniques contribute to these changes. For they make it possible to clad the entire building shell - roof and facades - in the same smooth skin. All conceivable geometric forms could now be enclosed with unswerving regularity. A seductive idea at a time when the never-ending, identical angular cubes were increasingly criticized and semantics began to gain new importance in architecture. The formal eclecticism that followed seemed to respond to the investors' and the clients' demands for unique, image-building structures; however, it too became a subject of criticism. Critical voices were raised even more as awareness of energy efficiency increased, for the smooth, sealed glass containers, were generally just that: encased in glass without operable windows and reliant upon artificial air-conditioning. The 13

curtain wall in its original sense had inevitably reached its limitations. A variety of architectural styles followed the International Style. Each reacted in a different way: PostModernism looked back to historic examples; Constructivism questioned traditional orders; and the proponents of High-Tech Design responded with structural components. But all share one common goal; to once again give the building skin a face.

1.3 Functions and classification "Architecture is an art of pure invention. Unlike the other arts, it does not find its patterns in nature, they are unencumbered creations of the human imagination and reason. In consideration of this, architecture could be considered the freest of all arts were it not also dependent on the laws of nature in general, and the mechanical laws of material in particular. For, regardless of which artistic creation of architecture we look upon, it was primarily and originally always conceived to satisfy particular material need, primarily that of shelter and protection from the onslaught of climate and the elements or other hostile forces. And since we can gain such protection only through combining the materials nature offers us into solid structures, we are always forced to adhere closely to the structural and mechanical laws."

(Gottfried Semper, 1854)

Despite changed cultural, economic, building technological and energetic parameters, .the principal task of architecture is still to create a comfortable "shelter." In other words, the fundamental aim of building is to protect people from external climate conditions, such as intensive solar radiation, extreme temperatures, precipitation and wind. In construction, the building skin is the primary subsystem through which prevailing external conditions can be influenced and regulated to meet the comfort requirements of the user inside the building. Like the skin and clothing of humans, this too, fulfils the tasks demanded of it by performing a number of functions made possible by means of the appropriate design and construction. Any serious inquiry into this context must address the following questions: 1.

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Function: What is the practical purpose of the building/the building skin?

Construction: What are the elements/components of the building/the building skin

and how are these elements assembled into a whole?

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Form: What does the building/the building skin look like?

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While these categories of observation and analysis have remained virtually unchanged for millennia, increased C02 emissions and the shortage of fossil fuels have precipitated a shift toward greater ecological awareness. As questions pertinent to sustainable building take centre stage in the planning process, this shift calls for a fundamental reconsideration of building concepts and the form and design of the building skin. Keeping this relationship in mind, the following factor should be added to the above list: 4. Ecology: What is the energy consumption of the building/the building skin during construction, use and demolition?

In terms of comfort, functional properties take precedence over structural, aesthetic and ecological aspects. However, all four categories must be given equal weight in a "total building system," since they are interdependent and bear a direct influence on each other.

Thus the physiological properties of an external wall are dependent on its structure, sequence of layers and material properties. The ecological characteristics in turn, are determined by functional i.e. physiological aspects such as insulating and shading properties. Questions of construction, too, such as the selection of materials determine the energy consumption in construction by virtue of their corresponding primary energy content. We begin by discussing the connection between the physical needs of the user and the resulting physical requirements of the building skin, followed by an overview of the functional properties and potentials of the building skin.

Comfort factors as parameters for building skin design Indoor air temperature The comfort zone for indoor air temperature ranges from 20-25 °C maximum. In summer, temperatures of up to 27 °C are still considered tolerable. When internal wall surface temperatures and the relative indoor humidity are properly adjusted, indoor air temperatures as low as 18 °C are still perceived as comfortable.

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Average surface temperatures Whenever possible, these temperatures should differ by no more than 2-3 K from the indoor air temperature; the differential between various surface temperatures in surrounding areas should not exceed 3-4 K. Air change and air movement While a minimal air change rate of 0.3/h is sufficient in unoccupied rooms, this value rises to 1.1/h during work hours. This corresponds to a fresh air intake of 40-60 m3/h per person.

Generally a value of 200 cm2/m2 of floor area suffices for intake and ventilation openings for natural ventilation. At the same time it is important to avoid draft by ensuring that air velocity does not exceed 0.15 m/s.

Relative indoor humidity Depending on room temperature, the comfort zone for relative indoor humidity ranges between 30 and 70%.

Luminance The standard values for luminance at the work place are dependent on the activity, the room layout and the proximity of the workstation to windows. Typical values lie in the region of 300 Lx for workstations near windows, 500 Lx for standard cubicle offices and 700 Lx for open-plan offices with a high degree of surface reflection or 1000 Lx for open-plan offices with medium surface reflection.

Lighting intensity The quality of lighting in a room is not only influenced by luminance but also by glare. The lighting intensity should be approximately 2/3 to 1/10 of the interior field lighting intensity.

Hence, it is important to select and position glare protection elements in a manner that provides evenly distributed daylight without glare, while avoiding unnecessary cooling loads in the interior space.

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Energy-related parameters of the building skin U-value The thermal transmittance (formerly U-value) indicates the amount of heat which passes through external wall structures in W/m2K. For opaque wall- and roof structures, typical values lie in the range of 0.3 W/m2K, easily achieved with standard insulating materials of 12-16 cm thickness. Modern insulating glass delivers values of 1.4 W/m2K and custom fillings will yield thermal transmittance values of as low as 1.1 W/m2K or less. For transparent and translucent external wall structures, one should take the potential of solar heat gain into consideration, as this can have a positive impact on the overall energy balance.

G-value The total solar energy transmission (g-value) indicates the percentage of solar radiation (wavelength 320-2500 nm) transmitted through transparent or translucent external walls.

This value is the product of the sum of transmitted radiation and heat emission from the internal pane into the room. Today, g-values of insulating glass panes lie between 60 and 80%.

Diminution factor The diminution factor refers to the sun-protecting effect of shading installations and indicates the percentage of incident radiant energy, which passes through a shading element. This value is dependent on the execution and installation angle of the shading system and provides information with regard to the heat gain in a room as a result of solar radiation.

Daylight transmission factor The daylight transmission factor indicates the percentage of daylight (wavelength 320-780 nm) which passes through the glazing. Current insulating glass panes typically have a daylight transmission factor of 70%. The constant changes in external conditions on a daily

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and yearly basis result in vastly different and in part conflicting requirements to which the external skin must respond in order to maintain comfortable conditions inside the building.

The impact of facade and roof design on energy consumption Sun protection systems The placement of sun protection systems has a decisive influence on the energy consumption of buildings. Calculations on conventional facades with east- and west orientation have shown that the energy consumed for cooling can be halved when external blinds are used, by comparison to a glass facade without sunscreen elements. Conversely, the use of internal blinds reduces the energy consumption by no more than 20%. Sunscreen elements are required to prevent overheating in all building types, especially for buildings with high internal cooling loads and/or a high percentage of glazing, e.g. most administration or office buildings. Fixed, stationary systems do not allow for adjusting the shading element to the position of the sun, and this can result in functional disadvantages with regard to shading, transparency and daylight use. Moveable systems can be adjusted to respond to changing solar altitudes over the course of a day and in different seasons, allowing for individual control of the sunscreen elements, optimal shading and maximum use of daylight. It is important to point out the disadvantages of internal sunscreen elements, because the solar radiation absorbed by these elements is transmitted into the room. In summer, this results in unwanted additional cooling loads. In winter, the potential heat gain may be used to increase the room temperature. Systems mounted behind glass, and thus protected from the elements, are easier to build and to install. This is equally true for double-skin facades, where a great variety of manipulators can be installed behind a protective shield of single glazing. Since these systems are protected from dirt and pollution, they allow for the use of elements with sensitive i.e. highly reflective surfaces for daylight redirection. With elements installed into the cavity between insulated glazing, the cleaning- and maintenance effort is potentially reduced even further (and the life cycle increased), for example micro-grid and prism systems. Despite the advantages offered by weather-protected shading systems, external sunscreen elements are still the most advantageous option due to the direct convection of heat gain to the outside. Nevertheless, 18

it is important to consider climate conditions and wind resistance when selecting the relevant components, since high wind loads can be a potential threat.

Anti-glare systems The main task of anti-glare systems is to prevent extreme contrasts in lighting intensity, an issue that is especially important in office buildings with monitor workstations where visual comfort must be maintained. This is the principal difference between anti-glare and sun protection systems. A variety of different systems can be used to mute and scatter intense light. These are: Curtains, Horizontal blinds, Vertical blinds, Venetian blinds, Screens, Translucent glazing and Electrochromic glazing. Whenever these systems are used it is important to avoid reducing daylight transmission to the point where artificial light has to be used or to impede visual contact between inside and outside. Textile anti-glare systems, screens and perforated aluminum louvres are practical options. The position of an anti-glare system in relation to the internal glazing layer determines the amount of heat gained in the interior as a result of radiation. By comparison to an office building with external sunscreen elements, sun protection glazing combined with an internal anti-glare system leads to an approximate increase in heating requirements of 20-30% as a result of the reduced radiation transmittance, and increased cooling energy requirements by 10-20% as a result of the heat gain in the anti-glare system.

Daylight use

The use of natural daylight is important because minimizing artificial lighting has a direct impact on energy savings. . The common approach is to use materials with low thermal transmittance factors, low emission properties to decrease heat loss by radiation, and highreflective foils or surface coatings to reflect heat radiation.

Natural Ventilation Aside from the above-mentioned parameters for regulating the energy balance, the building skin plays an important role in terms of the natural air exchange in buildings. Meeting requirements for air hygiene is the key factor in this context, with a special focus on the correct amount of ventilation to minimize heat loss by ventilation in times of cool outside temperatures. Free ventilation through existing openings in the building skin is generally sufficient for rooms whose depth does not exceed the height by more than 2.5. Dependent 19

on the manner of opening, as well as the location and position of the operable element, this solution achieves air changes between 0.2 and 50 L/h. Designing the building skin specifically with these natural principles in mind, e. g. the stack effect, can help to achieve natural ventilation even in the case of great room depths.

Other functional aspects In terms of comfort and safety, sound insulation and fire protection are additional important properties of the building skin. With regard to sound insulation, the building skin should be designed to reduce external and internal noise to a comfortable level. This is achieved by using materials whose mass enables them to reflect existing sound. Another option is to generate sound insulation by absorbing sound energy and converting it into heat. The minimal values for acoustic insulation rates in external building components range from 50 to 75 dB. Another function paramount in terms of safety of the users is to prevent the outbreak of fire or explosions; it must also counteract the spread of flames, heat and smoke.

Moreover, the structure must maintain its load-bearing capacity for a specified period of time and the layout must facilitate effective firefighting measures. External skin construction can be classified above all with regard to the combustibility of its materials and the fire resistance period of building components and load-bearing components. The following aspects are covered by fire resistance codes: walls, supports, floors, girders and stairs, which prevent the spread of fire and smoke as well as the penetration of radiating heat; transparent building components, i.e. glazing, which prevent the spread of fire and smoke but not the penetration of radiating heat; non load-bearing external walls; and doors and gates. For building skins it is therefore imperative to verify the building codes in each jurisdiction and to check specific guidelines for fire protection, which may limit the choice of building materials or construction type. For the purpose of fire protection, the focus is above all on load-bearing and room-enclosing walls, such as walls along emergency routes, in stairwells and on firewalls. These building components must deliver a fire resistance period of 30 to 120 minutes in the case of fire depending on building category and use.

The building skin as power station Before low-cost fossil fuels were widely available, the efficient use of heating energy and the principles of solar energy use were essential considerations in the design of buildings and building skins. Material selection, orientation of the building volume towards the sun, exposure, plans, and the design of facade- and roof 20

surfaces were all harmonized with the conditions dictated by the site. These are, among others, the local climate, the topography, the availability of materials for construction and combustible material for building operation. Over many centuries, a culture of building evolved, which demonstrates the direct link between functional requirements and external appearance, a link that is still visible today in traditional buildings. The drastic changes in the energy sector, in particular the ready availability of inexpensive fossil fuels and electricity, had a lasting impact on this traditional link. The relationship between local conditions and their impact on the built environment was more or less nullified. Only the realization that fossil fuels are an exhaustible resource and that the burning of coal, oil and gas presents a grave danger for the environment and the population, prompted planners to change their attitudes. Throughout Europe, approximately half of the consumed primary energy is consumed for the construction and operation of buildings. A radical reduction of energy consumption, coupled with the use of solar energies, is therefore the only logical and sensible solution to the problem of dwindling energy resources and environmental destruction.

Solar energy can be utilized twofold. Direct use is mainly concerned with orientation, plan and the design of the building and its components, especially the facade. Applied to the building skin, solar energy is used for natural ventilation (making use of thermal lift and the resulting pressure differences), for lighting interior spaces with daylight, and for heating interior spaces by harnessing the greenhouse effect. There is a wide range of systems from which to choose from for collecting, distributing and storing the available energy. Buffer zones, transparent heat insulation, aerogel glazing and high-insulating glass with U-values below 1.0 W/m2K widen the field of options for direct solar use and reduce heat loss by comparison to conventional insulated glazing. Components and systems, such as massive wall components faced with translucent heat insulation, make it possible to use the solar energy stored during the daytime to provide heat in the evening and early night hours. As to daylight use, one should consider micro-grid systems which enable a more efficient use of daylight, especially for office and administration buildings where higher cooling loads and user comfort requirements come into play. As its name indicates, indirect use refers to indirect application of solar energy through collectors that is autonomous systems, which can be integrated into the building skin. Indirect uses of solar energy include the heating of 21

water and air for interior space heating or for domestic/industrial water consumption. The conversion of solar radiation into cooling energy is yet another application where solar collectors are used in combination with heat absorption pumps or thermal/chemical storage systems. Photovoltaic elements have become increasingly popular in recent years for generating electrical power as a result of technological progress in this field, state subsidies and the development of panels that are easy to integrate. A wide range of applications has been developed for the building skin. Building materials, components and techniques must be carefully selected with the building concept in mind and harmonized with each other.

Both in the area of the roof and the facade, the building skin offers a variety of options for applications capable of meeting nearly all energy requirements, provided the systems, combination and storage options are employed accordingly.

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2. Perforated building skins in the Mediterranean and the Indian subcontinent

Figure 1 Jalli patterns

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The architectural and urban production of the old cities or villages stemmed from the nature of each society, and reflected the realistic image of life of each community (Y. Waziri, “Islamic Architecture and The Environment”). The relationships between the traditional cities and the socio-economic and socio-cultural contexts are also connected to the climate and to the environmental context. Many examples showed that the urban fabric of the old cities was derived from the dynamic synthesis of environmental, social and cultural factors.

Streets, alleys, and squares played an integrative role on the environmental and sociocultural levels. Furthermore, buildings were interlocked to each other (back to back buildings), as one system considering environmental role and socio-cultural connections.

This was common in the tropical and in the temperate climatic regions, a thermal balance was obtained in the traditional buildings to provide a thermal comfort for occupants in hot summer and cold winter, during the day and at night. The balance was evidential in the flooring system, in the underground floor, and in the setbacks of upper floors (M. Salqini, “Environmental Architecture”).

Perforations therefore emerged as a function in order to (a) enhance the integrative system, (b) allow the passage of natural air, (c) provide an indirect natural lighting, and (d) produce shade and shadows.

In addition to its important role in achieving the privacy for occupants. The use of perforation has endured later in modern cities, in urban expansion zones, in urban fringes, or in rural contexts as a functional response to the climatic conditions to some extent. Three different approaches can be seen here: an approach during the 20th century, which was disconnected from the past, by using the perforation slightly in a functional way (e.g., ‘Notre dame du haut’, ‘Unité d’habitation de Marseille’, and ‘Maison de Jeunes’ by Le Corbusier). The second approach was a disparity of perspectives between imitating, copying, or reshaping of the traditional architectural perforated models in their form, accompanying with other individual innovations that took both function and identity into 24

consideration (e.g. ‘Dar Assalam’ by Hassan Fathy and ‘Institute of the Arab World’ by Jean Nouvel). Thirdly, by the beginnings of the 21st century, a new rising trend of perforation has emerged in the world, by a significant change of techniques, technologies, functions, materials, and other related aspects (e.g. ‘Abbink X de Haas House’, ‘Seville Ceramics Museum’, ‘San Telmo’ Museum Extension). The contemporary concepts of buildings’ envelopes reflect the complexity of themes focused not only on environmental design, where the external appearance of a building was recognized, but also on the relationships between indoor and the outdoor environments. Accordingly, the connection between the contemporary trend and the traditional solutions has the opportunities to rethink of the future advancements in building envelope in terms of shape, form and performance. (“Technological and behavioral aspects of perforated building envelopes in the Mediterranean region” Maria Luisa Germanà, Bader Alatawneh ). Perforations have been employed in façade designs throught the ages for their climatic performace and the identity it brings brings forth with their various individualistic designs.

2.1 Types of traditional perforations 1. ‘Mashrabiya’ is one of the leading attributes of the Arab-Islamic architecture; it can be observed in the old cities of Baghdad, India, Damascus, Cairo, Jeddah, Tunis etc. The ‘Mashrabiya’ has many functions; controlling the passage of daylight, controlling the natural air flow, cooling of the natural air, and assuring a considerable level of privacy that is essential in the conservative Islamic communities. According to Hassan Fathy, the south sunlight entering a room has two components: the direct high-intensity sunlight and the lower intensity reflected glare. The perforations of ‘Mashrabiya intercept the direct solar radiation, and soften the uncomfortable glare. The ‘Mashrabiya’ provides security and its form is considered as an aesthetic value. It is covered by a wooden lattice (a structure consisting of strips of wood crossed and fastened together with a certain shaped spaces left between them). It is used as an archetypical element to provide privacy which is a main factor (visually, acoustically, and olfactory) in Arab-Islamic culture (O. Zukelpee, A. Rosemary, B. Laurie, “Privacy, modesty, hospitality, and the design of Muslim homes: A literature review”). The latticed screen has openable 25

windows which provides flexibility for the interaction between users and the envelope. As observed and mentioned there, the exhibited archaeological models of

Figure 2

Example of Mashrabiya (house of ahmad katkthudaal razzaz)

‘Mashrabiya’ in the Louvre Museum, shows that the terracotta material was also used historically for the latticed screens in India and Iran.

2. ‘Jaali’, often confused with the Mashrabiya is a similar screen but it usually done in stone such as marble and red sandstone. Both Jaali and Mashrabiya are used in religious and secular buildings. Jaalis are employed in palaces, mosques and even tombs and mausoleums, used as windows, decorations over portals etc. Mashrabiya are mostly used in housing and public buildings such as mosques and hammams, but rarely in tombs and mausoleum. The Jaali has been used in both Islamic and Hindu architecture throughout India, simple geometric forms characterizing these Jaalis.

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Figure 3 jaali screen of tomb of Salim Chisti, Fatehpur Sikhri

3. ‘Qamariya’ is a sort of nearly semi-circular openings. The first use of ‘Qamariya’ was before 4000 years ago in the era of the state of Sheba in Yemen (T. M. Smith, “Yemen: Travels in Dictionary Land-The Unknown Arabia”). It was mostly covered by a coloured glass, and was located above an external window, or above the main door, to produce a coloured daylight inside the internal spaces as an aesthetic value. The perforation of ‘Qamariya’ had several shapes, decorations (foils or leaves patterns), colours, techniques, etc. Similar elements were used in the Gothic architecture, in another shape and with different meanings, to play a role in 27

the symbolism of light (B. Fletcher). The perforated roofs or domes are sometimes classified as ‘Qamariya’, but they were a perforation into the roofs or domes, by making small cylindrical holes, to enhance the passage of daylight to the interior spaces that require extra-lighting, without prejudice to the concept of privacy (e.g.

Ayoubi Castle, Halab Syria, & Turkish bath, Hebron - Palestine). Sometimes, glass bottles or something else closed the holes, to prevent rainwater from going inside.

Figure 4 The perforated domes and roofs in Hebron – Palestine (above), Semi circular qamariya (below)

4. ‘Taqa’ is a small simply-shaped opening (rectangular, square, etc.). It was used in a linear, in a diamond, or in hierarchical arrangement at the end of the building’s 28

facades or above windows and doors. These elements played a good role in facilitating the natural ventilation, and in increasing the passage of natural light into the building.

Figure 5 Taqa patterns for window openings and facades

2.2 Daylight performance of Jaali Screens.

Jaalis have been part of the magical aura of Hindu and Islamic architecture since late. Their many features including its primary purpose of modulating light. Jaali screens allow reflected light that has a spectacular diffused glow into the room, preventing direct beam radiation and glare. Also, the smaller openings in the perforation allow acceleration of slight breezes into the room at the same time defending the interiors from strong gusts and winds. Interestingly enough, the patterns on this high performance screen has not evolved merely from artistic imagination but has more to do with environmental responsiveness in the most intricate way. The following sections highlight the hidden size ratios and light modulating capacities of Jaali screens. (The stone Jaali – Indian architect and builder, Dec 2014)

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Figure 6 figure showing solid void relationship

Solid void relationship The relationship between carved and uncarved, with implications from both the technique of the craft and the intended performance of the screen, reflects in the architectural character of the resulting facade. The limitations of carved sandstone have as much to do with the presence of solid as both the need for, and protection from, light. This relationship was measured by analysing the area of the elevation of the jaali. For facades in all cardinal directions, the solid is typically between 40% and 60%, and void between 60% and 40%.

Overhang ratio The maximum depth of any individual opening in the Jaali over the thickness of the stone is the overhang ratio. In all cases, this falls between .8 and 1.2. Which means that any opening is roughly as deep as it is tall. There are no remarkable differences between jaalis 30

oriented differently, most likely because the jaali is effective for the most extreme scenario, and then repeated on all facades. In a scenario where pieces are essentially prefabricated and used in a system (or pre-crafted), the efficiency of a single repeatable solution makes the task much easier.

Figure 7 solid void ratios of different case studies.

The following three types of Jaali screens were chosen for analysis - the 40% solid 60% void case, the 50% solid case and the 60% solid 40% void case, illustrated in the following figure.

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Figure 8 dimensions of typical three cases

By averaging the many types of jaalis, a model for simulation was derived. The simulation was done in Radiance, with a model built in Ecotect. Radiance is one of the most advanced simulation engines for daylight and lighting. In the simulation, the derived jaali is placed in a 3x3x3m room and tested at 9am, 12pm and 3pm on March 21, June 21 and December 21, to evaluate illuminance, uniformity ratio, and glare. Illuminance measures, here in lux, the amount of light falling on a surface. Uniformity ratio describes the uniformity the luminance (or light reflected from a surface) on a working plane. Glare occurs when the difference in brightness between two neighboring surfaces is too high, which affects the eye's ability to adjust for brightness. It is what causes people to see spots. Brightness ratios of 1:3 are acceptable on a work surface. 1:10 in the immediate cone of vision, and 1:40 in a room.

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Figure 9 image of glare renderings

Jaali glare renderings The findings show that the thickness makes all the difference. The highest levels of both illuminance and glare occur with a solid-void ratio of .67 (40% solid. 60% void) and an overhang ratio of .8. An increase in the solid-void ratio at a particular thickness creates a more uniform distribution and reduces glare, but also reduces illuminance. An increase in thickness also reduces illuminance and glare. According to this study, for a typical contemporary office building, a solid void ratio of 1.5 (60% solid, 40% void) and an overhang ratio of 1.2 (60mm thickness) produces the most uniform distribution with least glare and best illumination levels ranging from 100Ix to 800lx. why it matters Could buildings work better now if we thought about jaalis as they once were, with thickness and and overhang ratio around 1? In its translation in contemporary design, this perforated screen has often been flattened into a perforated sheet. This sheet does block some direct beam radiation. But it completely misses the power of the thick jaali, the one whose depth operates as an extending chhajja wrapping each opening, and whose thickness also absorbs some of the heat of the sun, working to keep the thermal lag in action and reduce the building's peak temperatures. Buildings today could immensely benefit from a 33

jaali conceived as it previously performed; one whose thickness was tuned to cut the sun for a measured illuminance, and whose material also worked toward maintaining the cool inside.

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3. The modern take on perforated screens – Park Hotel, Hyderabad

When we think about how the buildings have evolved over the years, the different changes that shaped new building designs, with glass playing a very crucial role in reinventing the building envelop and in some cases becoming the building envelop by itself. The traditional perforations such as the Jaali and the Mashrabiya were merely openings that perforated the main façade. But when large expanses of glass became the norm for decreasing the barrier between the inside and the outside and for air conditioning, the perforated screens themselves were reduced to the role of shading devices for these large glass facades. Now we look at combinations of these screens optimized to work with glass in harmonious ways to reduce the cooling loads on these modern buildings not compromising on the continuous barrier free views.

Figure 10 Park Hotel, Hyderabad – façade at night

The case study is a building and exterior envelope design of a 250-room boutique hotel for the Appe jay Surrundra Park Hotel Group in Hyderabad, India. The Park Hotel Group

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wanted the hotel to reflect the highly optimistic and sustainable culture in a growing India through a forward-thinking architecture. This is the first LEED Gold rated Hotel in India.

Climate in Hyderabad Hyderabad lies at 17°20’N 78°30’E in the Andhra Pradesh state in central India. It is in the Tropical Monsoon region. Summer months between March and May experience a large diurnal temperature swing between 25°C to 42°C. The Monsoon season stretches from midJune to September and brings heavy rains and prevailing wind from the northeast. The fall season or “post monsoon” is characterized by high humidity with minimal rainfall. The winter months carry much cooler temperatures and pleasant breezes that create opportunities for passive cooling and natural ventilation. The temperatures range from 20°C to 32°C (humans are most comfortable in a range between 18 and 25 degrees, depending on wind speed and humidity). What is significant here is the high solar radiation, particularly in the winter season from December to April. The direct solar radiation drops significantly in the summer from June to August, as the monsoon season mitigates the direct solar gain through the building envelope. Wind analysis reveals that the prevailing wind during the monsoon is from the west/southwest. Building outdoor spaces should be positioned in such a way as to protect them from the higher winds and wind-driven rain in the summer months.

Figure 11 How the form utilises the prevailing wind conditions.

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“Our physical environment must be thought of as being of composite structure, formed of many distinct, coextensive and coexistent yet interacting elements which may actually be viewed as complete sub environments” (James Marsden Finch, American Building). He describes seven types of “environments” that are only concerned with those factors that which act directly upon the human body and which can be immediately and directly modified by buildings. For the purpose of the climate analysis, five of the seven environmental parameters are used: thermal, aqueous, sonic, atmospheric, and luminous.

The thermal environment in Hyderabad consists of low diurnal swings and consistently high temperatures all year. The aqueous environment is characterized by the high relative humidity and high levels of rainfall through the year. It presents an opportunity for water collection during the monsoon months. The sonic environment relates to acoustics and ambient noise that impact the building user. It manifests itself in the building through internal-borne sound such as vibration from equipment or from external sound such as train horns and car traffic. The luminous environment pertains to the spectrum between 380 and 700nm that allows for visual light to be perceived. Arguably, a balance between the luminous and thermal environments is the most important aspect of design in this climate.

Thus, the design prioritized strategies that struck a balance between these two parameters.

The next step was to focus on leveraging the impact of ‘passive’ strategies before designing the mechanical or ‘active’ systems. In order to develop this new low energy model, perforated screens were introduced to regulate the amount of solar radiation falling on different parts of the building and the orientation, massing and roofing design fully optimised to minimise the solar gain of the building and to take advantage of the prevailing wind conditions throughout the year. The form also uses the venture effect to create a low pressure zone on top of the room that creates a constant influx of air getting sucked in from the large void on the south façade. Venturi system utilizes Bernoilli’s Principle which states that in fluid flow, an increase in velocity occurs simultaneously with decrease in pressure.

This Roof Geometry helps to mitigate heat generated from facade and preserve microclimate.

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Figure 12 Building orientation is optimized to receive solar radiation at large angles and maximize view towards the lake on the east.

The Faรงade The intuitive design response to all these parameters and analysis was a perforated metal screen fulfilling a desire to mask guest room areas without reducing views. The initial geometry of these perforations was inspired by regional vernacular and craft-making traditions embodied in the crown jewels of Nizam. The Nizam were the ruling class in the region who, at one point, had the most valuable jewel collection in the world. The large leaf-shaped geometry was a perforated in flat metal and combined into a repeating pattern across the faรงade.

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Figure 13

Faรงade pattern detail

The micro perforations in the wall were further optimised using computer software analysis. The final design solution is a computer-derived pattern composed of custom panels that could be fabricated through a programmed laser punch machine that the fabricator had purchased. The pattern creates a range of gradients that change from open or "perforated" to closed or "embossed" shapes. For example, the south faรงade has more open perforations while the west has more closed embossed shapes due to increased solar exposure.

Figure 14

Manufacture of perforated screens using Laser press machines

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For the material out of which the screen had to be made, the process started with stainless steel. Stainless steel was initially preferred by the team for its visual quality and low maintenance, but was found to be inappropriate for three reasons. First, the dyes created to do the double punch emboss process were not strong enough to conduct multiple repetitive operations without breaking. Second, once the panels were constructed, they were heavier and harder to handle than aluminium causing problems in shipping and installation. Third, the air in Hyderabad is very dusty and was found to have a high degree of suspended iron fragments. These fragments had the potential to become embedded in the stainless steel and rust. The only way to prevent this was a continuous coat of oil which would have been very time intensive and expensive to apply. Another concern of the design team was oilcanning of the metal panels due to a release of internal stresses once the panels were deformed for the pattern. Oil-canning is the deformation of a flat sheet of metal during fabrication caused by stresses induced in the manufacturing process. The oil-canning was more apparent on the stainless steel panels because of the stresses generated from deforming the panel. The shape and depth of the perforation created structural stability. The screens ultimately used on the project were fabricated out of aluminium. They were malleable and durable enough for repetitive punching. A multiple powder coat finish then provided the final layer of protection. The high recycled material content of aluminium also made it an ideal material selection for the sustainable goals of the project.

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Figure 15 façade installation details

The final solution for the Park Hotel evolved from an intuitive response to a detailed environmental analysis and collaboration with fabricators and consultants. The design performance and ecological impact of the building developed through a collaborative process in which all groups had input and impact on the final design. This process resulted in 20% reduction in energy loads from a baseline design. The optimized design would not have been possible without the use of building information parametric modelling and environmental analysis to inform and produce the metal screen. Such designs have their own inherent aesthetics along with what they were designed for – superlative climate control.

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Project credits Key design team: SOM New York.

Environmental Consultants: Environmental Design Solutions, New Delhi HVAC Consultants: Spectral Services Consultants, Noida Acoustical Consultants: Cerami Associates, New York Curtain Wall Contractor: Permasteelisa India Ltd, Bangalore Client: Apeejay Surrendra Park Hotels

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4. The new Mashrabiya – Al Bahr towers, Abu Dhabi When climate is something that is dynamic, it only seems logical that the façade created to control this constantly changing force also be dynamic. This led to a thought process that questioned the effectiveness of traditional “stationary” perforations. Now the questions were, what if the façade could change and modify itself according to the weather? The

Figure 16 Al bahr tower

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answer was an adaptable façade which could interpret climatic data and adjust its aperture to allow more or less sunlight to penetrate into the building. An example of an adaptive façade modified on the concepts of the traditional Mashrabiya pattern has been used to create an envelope around the twin Al Bahr towers. Located in the financial centre of Abu Dhabi, the award winning Al Bahr Towers consist of two quasi-identical, 150m tall buildings that embody an adaptive facade wrapping around the towers. The towers feature an innovative dynamic shading screen, the Mashrabiya, which enhances the sustainable criteria of the development by optimising the use of natural daylight whilst controlling solar gains. Following an international design competition in 2008 the design bid submitted by London-based architect AHR, together with Arup as multidisciplinary engineering designer, was chosen as the winning entry by the client body.

A key design driver was to develop a building envelope that was both efficient and iconic, related to Islamic architecture. The conceptual designs embodied a novel approach to reduce the effects of the high ambient temperatures and intense solar radiation that characterize the local environment. From the start, it was evident that the towers’ cladding design and its thermal, solar and lighting performance would play a crucial role in the project’s success. The idea adopted by the design team was radical yet simple – to control solar gains by introducing an external movable shading system instead of relying solely on the glass to filter the solar radiation. The team drew inspiration from the Mashrabiya, a form of shading screen that had been used for centuries in Islamic architecture to protect the building occupants from the intense sun whilst providing comfortable internal spaces and sustainable buildings in a harsh environment. The challenge was to re-interpret this concept in a modern architectural language and to apply it to 150m high towers having complex geometries.

A philosophical leap in the design process was to incorporate an adaptable shading system that attained the above benefits whilst controlling solar gains into the towers by filtering the direct solar radiation. Such a system would reduce the internal surface temperature of the framing and glass, and improve the working conditions and the thermal comfort by minimizing any radiative effect from a hot surface into a mechanically cooled environment.

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The solution was the innovative Mashrabiya adaptable shading devices which wrap the Al Bahr towers. In fact, the Mashrabiya became a key architectural theme in the towers’ design, reflected also in the structural geometry and the interior design too.

Figure 17 3D models of primary structure, façade and shading system

The complex elliptical shapes of the towers, both on plan and in section, necessitated a system that was more sophisticated than industry-standard louver systems. A triangulated shading system, opening and closing according to the sun position, was thus conceived similar to a big ‘umbrella’.

Performance The design team undertook extensive thermal modelling and 3D solar analysis of the effect that this unique active shading system would have on various zones of the towers at different times through the year. This process helped identify the required extent of the shading device and its regime of opening and closing. These studies also allowed the design team to derive the precise portion of the North facing facade where the shading was not required.

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Figure 18 3D solar analysis on central portion of tower (Arup)

The vision area within the tower floor plates consisted of floor to ceiling high double glazed units, with laminated inner and monolithic outer panes, both heat-strengthened. In an intense climate as Abu Dhabi, with maximum temperatures of around 45˚C and very high solar radiation levels year-round, the primary aim was to control the solar radiation.

Conductive gains due to temperature difference are normally less of an issue. However, in heavily shaded buildings with reduced gains due to solar radiation, the conductive component becomes more and more relevant. For this reason particular attention was paid to enhance the thermal performance by specifying Argon filled double glazed units and introducing thermal breaks where the brackets supporting the Mashrabiya penetrate the thermal line.

Materials The exceptional levels of transparency adopted for the towers and the resulting increased daylighting were made possible by a careful selection of the mesh material of the movable Mashrabiya shading system sitting in front of the façade. Different options were investigated to select the most appropriate fabric for the triangular panels, and PTFE-coated glass fibre mesh was identified as the most durable and best-performing solution. PTFE fiberglass coating is capable of withstanding high temperatures and it is a ‘self-cleaning’ fabric, which helps reducing cleaning and maintenance time. The final fabric presented an open area of 15% and a light transmission of 25%.

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Figure 19 View from the inside through the PTFE fabric. The supporting frame is a combination of aluminium and duplex stainless steel, to withstand the aggressive marine environment.

Faรงade The faรงade consists of a facetted unitised curtain wall system. The panels are typically 4200mm high and of variable width due to both the barrel shape of the towers on elevation

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and the floor plate that vary in dimension across the height of the towers. The floor to ceiling vision area is 3100mm high and the resulting spandrel area is 1100mm high. The spandrel consists of two zones of 350mm high double glazed units and back insulation, with the cavity between the glass and insulation pressure equalized to the outside. The central portion of the spandrel is a 400mm high metal clad fascia. All the profiles are in aluminium, thermally broken and natural anodized. The glass is structural silicone bonded on 4 sides and the aluminium extrusions were designed to accommodate a small carrier frame in case of glass replacement. Mechanical restraints were introduced to carry the dead load of the double glazed units. An additional metal fascia is installed on the outside, running in front of the unitized panels, replicating the honeycomb geometry of the internal primary structure. These aluminium panels are fixed to the curtain wall with small brackets and can be easily removed to allow access to the panel joints in case of replacement.

Design process and testing Hand sketches, paper models, small scale physical models and 3D digital models were the preliminary steps embarked on to refine the competition idea and to prove to the client body that the innovative concept was feasible. As the design progressed, it soon became evident

Figure 20 Installation of the Mashrabiya panels. The shape of the building in plan and elevation led to 22 different variations in the panel geometries

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that the interface between the Mashrabiya and the towers’ superstructure presented a key challenge. Various structural arrangements were assessed in the early design stages, and the creative and Collaborative input from the various disciplines (including structure, façade, lighting and architecture) resulted in the Mashrabiya shading elements being conceived as unitised systems, cantilevering 2.8m from the primary structure. This solution allowed each element to be replaced without affecting the structural stability of the whole system. The cantilevering stainless steel arms were detailed to allow a neat connection where the tapered ends of six adjoining panels meet at each node. In total each tower has 1049 Mashrabiya panels, weighing about 600 kg each.

As part of the façade technical performance specifications, a thorough testing regime was specified in addition to the performance targets and materials requirements. A key milestone in the design process was the assembly of a fully functional 1:1 scale prototype by the façade contractor responsible for the post-tender design development phase. The design was then refined and tested in a wind tunnel facility and in a climatic chamber. More than 30,000 opening and closing cycles were simulated at different temperature conditions, varying from 24°C to 60°C, and at different levels of relative humidity. Sand and salted water were applied regularly throughout the testing process on all the critical joints to qualify that the required durability life of actuators, bearings and mechanisms were attained.

Figure 21

Wind tunnel testing, 1:75 scale – pressure taps on open Mashrabiya panels

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The Mashrabiya panels cover 3 predefined positions – folded, intermediate, unfolded. The design allowed them to be re-programmed in any required configuration should this be

Figure 22 panels in different positions

deemed preferable in the future. The Mashrabiya panels are grouped in sectors and are operated by a sun tracking software controlling the opening and closing sequence according to the sun’s position. It is possible to override the system to control individual panels. The control system is linked to anemometers and solar radiation sensors at the top of the towers, to adjust the position in case of extreme wind speed or prolonged overcast conditions.

Benefits of the shading system The presence of a movable external shading helps to significantly reduce the solar radiation, only when and where it is needed. Assuming as a benchmark a glazed envelope achieving a g-value of 0.20 and a light transmission of 25-30% (common figures in the region), the combined shading and glazing systems adopted in the Al Bahr Towers reduces the solar gains by more than 50%, achieving a much higher level of light transmission.

A preliminary assessment carried out during the design phase showed how the external Mashrabiya helped reduce the capital cost of the cooling system by approximately 15%, achieving a 20% electricity load saving as a result of the smaller cooling plants. This strategy also played a major role in reducing the carbon footprint of the building, reducing the CO2 emission by approximately 20% and helping it obtain a LEED (Leadership in Energy and Environmental Design) silver assessment. The external shading maximize the useful daylighting penetration. It also reduces the amount of working hours when internal blinds need to be lowered to control any glare effect, significantly increasing the lighting energy savings in the process. An enlightened client body, an inspired architectural team and more than 300 Engineers across 14 different disciplines worked together delivering a 50

truly integrated design to achieve a unique project with a novel shading system. The team challenged conventional thinking and managed to turn a great intuition into reality, enabling a paradigm shift in the design of tall buildings and setting a benchmark to be followed for many years to come. The project secured the 2012 Council for Tall Buildings & Urban Habitat’s (CTBUH) Innovation Award, and it was listed amongst its 20 most Innovative Tall Buildings of the 21st Century. It featured in the November 2012 Time as one of the ’25 best inventions of the year’. Al Bahr Towers also won the 2013 Society of Façade Engineering Award.

Project credits Client: Abu Dhabi Investment Council, Abu Dhabi, United Arab Emirates.

Architect: AHR, London.

Multidisciplinary Engineering Designer: Arup, multiple offices (Façade, Structure, Building Services, Civil Engineering, Geotechnics, Lighting, Acoustics, Fire, Wind, Security, Traffic, Vertical Transportation, IT and Comm, Catering Consulting).

Façade A&M: Reef, London.

Architect and engineer of record: Diar Consult, Abu Dhabi, United Arab Emirates.

Cost Consultant: Abu Dhabi office of AECOM (formerly Davis Langdon).

Project manager: Mace, London.

Main Contractor: Al-Futtaim Carillion LLC, Abu Dhabi, United Arab Emirates.

Façade Contractor: Yuanda China Holdings Limited, Shenyang, China.

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5. The Future – A Real Skin

Adaptive facades maybe as climatically responsive as it gets but the search for the perfect façade does not stop there. “Why should human beings adapt to buildings? Why can’t buildings adapt to human beings instead? “This what Doris Kim and many architects like her ask, pushing the limits of technology and striving to find the ultimate. The best teacher is nature itself and the pursuit for optimisation brings us back to observing how nature deals with the elements. The notion of sustainability in building design is commonly associated with reduced energy consumption and carbon footprint. It is widely recognised that a substantial reduction in building energy use can be achieved through the application of passive design measures that allow increased exploitation of natural heating, cooling and light to maintain comfortable interior conditions for the longest time without the need for external energy inputs. However, in most cases even buildings with a good passive design require the occasional use of active (i.e. energy-consuming) building systems to ameliorate the effects of the changeable external environment. Adaptive building skins that are able to adjust and optimise their properties depending on the ambient conditions can help address the challenges of continuously maintaining occupant comfort whilst reducing energy use.

Contemporary adaptive systems tend to rely on technologically-imposed intelligence enabled by application and interaction of sophisticated mechanical and electronic sensors, control systems and actuators which results in a dependency on energy supply, high complexity and cost, and potential reliability and maintenance issues. This points to the need for further research into design approaches, materials and techniques that could combine the simplicity and low-cost of zero-energy bioclimatic design and the dynamic response of high-tech adaptive architecture. The inspiration for this ‘hybrid’ approach to adaptive architecture can be drawn from nature where elegance and functionality often coexist and the robustness and efficiency of responsive systems, such as conifer cones, is enabled by employment of the inherent properties of their constituent materials.

Application of materials with intrinsic sensitivity to climatic stimuli can therefore serve as an underpinning principle for development of simpler, yet more versatile adaptive building skins with passive embedded response.

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Hygromorphically responsive Skin

The evolution of the shape, structure and behaviour of natural responsive systems, such as pine cones, is defined by the necessity to maximise the use of the inherent properties of available materials. This principle forms the basis for a new approach to adaptive architecture that goes beyond the current performance oriented technological paradigm of sustainability and seeks to address a wider range of sustainable considerations by deploying materials with embedded responsive properties. Biomimetic hygromorphic (moisturesensitive) materials that employ the natural responsiveness of wood to moisture, can provide opportunities for the design of simpler yet more versatile responsive building skins which are passively attuned to the variable rhythms of the internal and external environment. Production of many of the modern man-made smart materials, is often complex, power-intensive and requires materials with limited availability which diminishes their applicability in large-scale building applications. For this reason, there is an increasing research interest in examples of natural responsive mechanisms that are architecturally scalable. One example of such mechanisms is the opening and closing of conifer cones.

The large seed-producing scales of the pine cones consist of two layers exhibiting different amounts of dimensional changes when exposed to moisture . As a result, the scales bend outwards in dry conditions and close in humid or wet environment. A similar actuation mechanism is also observed in a number of other natural systems with reversible moistureinduced response, for example, wheat awns and orchid tree seedpods. Conifer cones retain their responsiveness over a large number of cycles as the mechanism operates passively and is performed by the tissues of the fallen cones, which are no longer alive. The structure of the responsive scales of the pine cone can be replicated to produce low-tech low-cost artificial hygromorphic (moisture sensitive) materials (a.k.a. hygromorphs) consisting of active wood layers and natural or synthetic passive layers.

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Figure 23

Reversible moisture-driven opening and closing of pine cones.

Figure 24 Principle of the response of hygromorphic composites based on differential hygroexpansion (i.e. shrinkage or swelling) of active and passive layers

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“Similar to the woody tissues of the scales of conifer cones, hygroexpansion of wood is a passive material capacity resulting from its hygroscopicity (i.e. continuous exchange of moisture with the surrounding environment through processes of adsorption and desorption).� (Hoadley, R.B). The ability to adsorb water is not unique to wood, however, 54

unlike many other hygroscopic materials (e.g. paper and concrete), it is able to exhibit comparatively large dimensional changes resulting from variations in its moisture content and is characterised by good flexibility and low weight. This in combination with ubiquitous availability and low environmental impact of wood as a renewable natural material make it well-suited for the use in the active layer of hygromorphic materials. A range of synthetic polymers, fibre-reinforced polymers (FRPs) and other non-hygroscopic materials can be used in the passive layer to ensure its dimensional stability. Many of these materials, such as Polyethylene Terephthalate (PET), which is widely used and recycled, are characterised by substantially greater overall durability, toughness and better resistance to UV degradation than wood and can improve the longevity of the resulting semi-synthetic composites.

Recent research on hygromorphic materials has mainly been focused on testing of material responsiveness and demonstration of the dramatic aesthetic appeal of the technique through production of small-scale prototype structures with different shapes and arrangements of responsive elements. Several authors have speculated on the general categories of possible applications for hygromorphs as sensors or actuators or in larger scale applications such as building envelopes and roofs of stadiums and semi-indoor spaces. However, the wider challenges and opportunities of building integration and the potential functional and aesthetic applications of the materials in architecture are yet to be established. Since the building envelope serves as a barrier between the internal conditioned and the external unconditioned space, it is argued that the use of responsive materials to enable its adaptive behaviour and employ it for control over the interior climate and occupant comfort is one of their most promising building applications. For example, a cladding system comprising of hygromorphic materials could fold or deploy when exposed to rain (or in advance, by responding to high relative humidity) creating a watertight shelter and managing water runoff. In large-scale fully conditioned buildings requiring more substantial weather sealing, the responsive composites could be used as an active component of the building systems controlling air movement and the exchange of heat and moist air between the indoor space and the outdoor environment through continuous passive adjustment of porosity. In arid climate regions, hygromorphic building systems could be configured to help maintain thermal comfort through enhanced natural ventilation in hot dry weather.

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Alternatively, the response of the materials to changes) and condensation (adsorption of condensed water). temperature could be triggered by evaporation (relative humidity Whilst hygromorphs are not photosensitive, hygromorphic systems could be designed to control illumination and prevent excessive solar gain and glare based on the assumption of a link between relative humidity and the amount of available daylight. Responsive elements preinstalled into retrofitted modular cladding or integrated as part of the windows could be preprogramed to fold providing shading in dry sunny weather and open up in humid conditions when the sky is overcast to maximize the use of daylight.

Bloom – Doris Kim Sung Challenging the traditional presumption that building skins are static and inanimate, this project examines the replacement of this convention with one that posits the prosthetic layer between man and his environment as a responsive and active skin. Doris kim has demonstrated elegantly how such a screen that functions drawing on the principles of thermo bi metallic strips can outperform any stationary or stable façade. Her installation in Los Angeles combines 414 hyperbolic paraboloid-shaped stacked panels to create a free standing geometry. The panels combine a double-ruled surface of bimetal tiles with an interlocking, folded aluminum frame system. Like the undulation of the surface, the frame, by nature of its folds, is designed to appear on the inner or outer surface at the same cadence of the peaks and valleys. The final monocoque form, lightweight and flexible, is dependent on the overall geometry and combination of materials to provide comprehensive stability.

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Figure 25 The Bloom - A Temporary Installation at the Materials&Application Gallery, 1619 Silver Lake Blvd, Los Angeles, CA

The main goal of this installation is to demonstrate the efficacy of thermobimetal as an exterior building surface with two functions. The first involves the bimetal’s potential as a sun-shading device that dynamically increases the amount of shade as the outdoor temperature rises. The size, shape and orientation of the tiles of the tiles are positioned strategically to perform optimally to the relative angle of the sun by use of advanced modelling software. Reliance on digital modelling and physical panel testing prior to final installation is necessary to ensure top performance. The second function for the bimetal is

to ventilate unwanted hot air. By optimizing the contortion of individual bimetal tiles, any 57

captured heat would trigger the surface tiles to curl and passively ventilate the space below.

In both cases, numerous laser-cutting patterns, solar diagrams, computer analyses and material prototypes were studied, analysed and tested until the final parameters of the tile cross-shape was set. Thermobimetal is a lamination of two alloys of metal. Because each alloy has different coefficients of expansion, the sheet metal will curl when heated. In the case of BLOOM, reacting to changes in ambient temperatures and sun penetration, the surface can open to allow hot air to escape or close to prevent solar rays to enter.

The faรงade is often the defining element of the building in terms of its visual, tectonic and contextual expression. In this context, the possibility of responsive hygromorphic building skins and thermobimetallic strips that are in continuous formal interaction and synchronization with their ambient environment provides opportunities for creation of unique architectural designs, vividly different from the static structures that typify the current architectural production. The dynamic behavior of these cladding elements would give buildings with responsive envelopes a rich texture reminiscent of that of natural organisms. Responsive cladding that is attuned to the natural rhythms of the external climate would provide a direct visual and formal reference to the ambient conditions of the climate positively contributing to the subjective enjoyment of the design and psychological occupant comfort. Beyond the functional and aesthetic applications, the integration of climatically responsive hygromorphs into buildings has the potential to address wider concerns about the technological intensity of modern buildings as well as helping to move beyond the focus on resource efficiency towards a more holistic view of environmental well-being. It is this possibility to simultaneously contribute towards climatic adaptability and environmental performance and the expressive potential of the technology that probably provides its most progressive and viable building-related future applications.

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6. Designing building skins for the tropical climate.

The performance of building skins is very dependent on the context it is placed in. For the same reason the design of skins vary from one climatic zone to the other. A tropical climate is a climate typically found within the tropics, In the KÜppen climate classification it is a non-arid climate in which all twelve months have mean temperatures of at least 18 °C. Unlike the subtropics, where there are significant variations in day length and temperature to various degrees, with season, tropical temperature remains relatively constant throughout

Figure 26 Climatic regions of India

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the year and seasonal variations are dominated by precipitation. The Indian sub-continent can be broadly categorized into five regions with distinct climates. Out of the five, most of the southern part of India including Kerala falls under the warm-humid category.

Figure 27 Sunpath diagram for Ernakulam, Kerala

Building Orientation Buildings must be oriented in the north south direction so that the longer faced are exposed for shorter durations to direct sunlight.

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Figure 29 Showing movement of the sun with respect to building faรงade.

Figure 28 Best orientations for existing plan forms

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Perimeter to area ratio

Figure 30 showing perimeter to area ratio

In the hot - dry climate a smaller perimeter-to-area ratio (P/A) would result in less area exposed to radiation and lesser conduction heat gains.

Figure 31 design strategies

Shading strategies for windows and openings Shading is the most important building design strategy for comfort in the hot-dry climate.

Shading of openings like windows is very important and in any case the Window-WallRatio (WWR) should not be more than 60%. Effective day lighting is possible with a much lower WWR. 62

Figure 33 Different types of shading devices

Figure 32 Optimum solar shading

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Retrofitting In the transition between vernacular architecture towards something more contemporary, buildings in Kerala have seem to have lost their climatic qualities. Retrofitting can be seen as a quick fix to improve the energy efficiency of RCC buildings that has cropped up all over the state. For newer buildings, at least commercial ones any of the aforementioned building skins can be adapted during their design phase, but because a large percentage of buildings already exist that need performance enhancement, retrofitting is the first necessary step towards a greener State.

Figure 34

illustration showing schuco retrofitting system

a retrofit is easy because it can be installed while the building is still in use. This is how it works: 1. The old structure with an existing faรงade with an in-filled, reinforced concrete skeleton structure. 2. The load-bearing pilaster of the modernization faรงade is fixed to the building structure above a fixing bracket as a vertical load-bearing system. 3. The new window units are installed on the inside of the load-bearing pilaster, whilst the old windows initially remain in the faรงade. 4. After sealing the new window units to the building structure, the remaining building areas are insulated. 5. Installation and wiring of the concealed, flush-fitted solar shading system. 6. The different infill units, such as glass, sheet metal or photovoltaic units, can now be efficiently and quickly mounted on the installed 64

load-bearing structure. 7. Once the outside is complete, the old window units on the inside are removed. The reveals are clad with panel units made from wood, sheet metal or plasterboard. 8. The modernization is complete.

Figure 35 Figure showing the process of retrofitting a structure

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Variable Solar Protection Glass

Figure 36 Variable Solar Protection Glass

Modular aspects of the retrofit allow custom panels to be installed for windows as well as other openings. Variable solar protection glass stands one step ahead of today’s double glazed units. To complement the basic solar protection system that takes advantage of the façade’s own shadow, a new kind of glazing has been developed. This was designed to improve passive solar protection and has specifications that vary depending on the angle of incidence of the sun’s rays. A design that is specifically adapted to the orientation of each façade and the latitude of each building can be obtained by combining several sheets of laminated glass with various superimposed layers of reflective, semitransparent metal coatings. Unlike other products with similar specifications, the treatment applied to the glass can be customized and adapted precisely to each case and specific orientation of the façade. Thus, areas with greater visibility and different degrees of transparency can be incorporated into the same unit of glass. The formal result is a window of glass with a variable degree of reflection and transparency according to the interior and exterior environmental conditions in each case. As protection from the sun is incorporated in the glass itself, we eliminate the problems of durability and maintenance that are associated 66

Figure 37 image showing reflectance of variable solar protection glass

with standard elements of solar protection (blinds, awnings, slats, etc.). In addition, less material resources are needed to construct the façade. As this material is manufactured in the form of flat glass, it can be combined with other sheets of glass to provide, for example, units of insulating glazing with air chambers, low emissivity treatments or acoustic insulation. It can be used in any kind of wall or façade system The solar protection values that are obtained depend on the final composition of the glass, the orientation of the façade, and the type of layer used in the treatment. For example, in the case of glass made up of an exterior sheet 4+4+3 mm with the variable protection treatment described above, an air chamber of 24 mm and a laminated interior sheet of 10 mm with a low emissivity treatment, the solar factor varies between 0.33 and 0.14 for incident angles of 25º and 72º respectively, which correspond to the incidence at midday (12 am) on the summer and winter solstices, with a south-facing façade at a latitude of 41º. This variable solar factor provides passive solar protection with seasonal differentiation, without requiring sophisticated operations to regulate it or depending on the uncertain management of the user. This leads to greater reliability in the final performance of the glazed wall, which is of particular interest in buildings with a high proportion of occasional users: for example, public buildings with administrative and residential uses.

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Breathable glass faรงade This may be the solution to the large glass facades which house air-conditioned spaces that require huge amounts of energy for air cycles. This is a research project initiated by MArch student Andrei Gheorghe in collaboration with engineers Werner Sobek, TimMacFarlane at the Graduate School of Design Harvard. The project explores degrees of visual and climatic permeability by using glass. It introduces glass fins, which are twisted in order to allow for cross-ventilation and dichroic effects.

This is a porous facade system of operable lamellas by twisting glass. Glass has a certain ability to twist before it breaks. Longitudinal shaped glass fins are fixed in position at their endpoints and are twisted in their midpoints. This creates openings that can be beneficial for climatic or visual effects. Through the twisting operation, the glass fins become stiffer and withstand higher horizontal (wind) loads. The torsion capability of glass is therefore used with the aim to create a porous, air permeable faรงade prototype.

Figure 39 demonstrating the kinetic nature of the twisting glass facade

Figure 38 prototype in open and closed positions.

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This is a radical new approach towards using glass. Usually, twisting is avoided, due to the brittle behavior of glass. The author claims that applying torsion below certain limits will allow to create openable glass faรงade systems. This will help reduce mechanical ventilation (especially in commercial typologies such as shopping malls and administrative offices where large spans of glass facades are normally used) by allowing natural ventilation when needed. Through the use of dichroic glass visual color effects can be achieved through the twisting motion.

Figure 40

Simulated renderings showing effects of dichroic twisted glass faรงade.

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7. Conclusion New forms of generating energy will influence the design of the building skin as much as future developments in how we work and in office technology. Research on new materials, manufacturing methods and facade components is vitally important. This may well revolutionize the performance and image profile of the building skin in a manner comparable to the invention of the float glass process in 1955. High-performance computers and new testing methods complement the options for glass applications in construction.

Several types of building skin systems exist today and with combinations amongst themselves, the permutations possible are innumerable. The idea is to find the best solution for the task at hand. If ecofriendly targets and performance enhancements are the deciding factors during design, buildings of tomorrow can stop being the major contributors to India’s carbon foot print. The new technologies may be more expensive than conventional ones but incorporating them in the design is beneficial not only from a sustainable stand point but it is the more commercially viable option as these high performance façade systems pay off in the long run. Instead of stationary facade systems, today’s architecture is kinetic and adaptive in nature, this enables buildings to modify their performance and adapt to diurnal and seasonal changes and thus become more energy efficient.

To advance the issue of the building skin with a view to creating truly sustainable and enduring architecture, planning must be goal-oriented, responsible and sensible. A high degree of technical and creative ability is essential. The way to do this in Kerala would be to start with retrofitting the existing facades with variable solar protection glass and building integrated photovoltaics. Screening systems can be installed at least on the south side of the façade. For commercial applications, adaptive facades can be used which can remain closed during the day and open out at night to showcase the interior.

The enormous potential of the building skin must be realized from a structural, functional, aesthetic and ecological perspective to promote advances in the development of architecture that is oriented towards the future.

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8. References Christian Schittich, Building Skins. Germany: Birkhauser, 2001 Technological and behavioral aspects of perforated building envelopes in the Mediterranean region , Maria Luisa Germanà, Bader Alatawneh, Rabee M. Reffat.

Y. Waziri, “Islamic Architecture and The Environment”, Series of World Knowledge, Kuwait, 2004. (Arabic language).

V. Olgyay, “Design With Climate: Bioclimatic Approach to Architectural Regionalism”, Hardcover March 21, 1963. [3] M. Salqini, “Environmental Architecture”, 1st ed., Dar Qabis publishing press, Beirut, 2004. (Arabic language).

T. Abdelsalam, Gh. M. Rihan, “The impact of sustainability trends on housing design identity of Arab cities”, Journal of Housing and Building National Research Center, vol. 9, 2013, pp. 159-172.

H. Fathy, “Natural Energy and Vernacular Architecture”. Chicago: University of Chicago, 1986.

O. Zukelpee, A. Rosemary, B. Laurie, “Privacy, modesty, hospitality, and the design of Muslim homes: A literature review”, Frontiers of Architectural Research, Elsevier. vol. 4, 2014, pp. 12-23.

T. M. Smith, “Yemen: Travels in Dictionary Land-The Unknown Arabia”, hardback & paperback, U.S., 1997.

B. Fletcher, “A History of Architecture on the Comparative Method for the Student, Craftsman, and Amateur”, 20th ed., Routledge, London, 1996.

J. Awad, “Rural Houses in Palestine”, Riwaq, Ramaalah, 2012. (Arabic language).

B. Alatawneh, M.L. Germanà, “Earth for Social Housing in Palestine: An alternative for a sustainable refurbishment of buildings’ envelopes”, The International Congress on Earth Architecture in North Africa, Marrakesh, 2015. (In press).

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The Al Bahr Towers – the real envelope, Giorgio Buffoni MSc CEng MCIBSE IntPE(UK) Arup, 13 Fitzroy Street, London W1T 4BQ, United Kingdom Banfill, P. and Peacock, A.: Energy-efficient new housing–the UK reaches for sustainability, in Building Research & Information 35 (2007) issue 4 Sadineni, S.B., Madala, S. and Boehm, R.F.: Passive building energy savings: A review of building envelope components, in: Renewable and Sustainable Energy Reviews 15 (2011) issue 8.

Loonen, R.C.G.M., Trčka, M., Cóstola, D. and Hensen, J.L.M.: Climate adaptive building shells: State-of-the-art and future challenges, in: Renewable and Sustainable Energy Reviews 25 (2013).

Menges, A. and Reichert, S.: Material Capacity: Embedded Responsiveness, in Architectural Design 82 (2012)issue 2.

Pawlyn, M.: Biomimicry in architecture, Riba Publishing, London, 2011.

Guy, S. and Farmer, G.: Reinterpreting sustainable architecture: the place of technology, in Journal of Architectural Education 54 (2001) issue 3.

Holstov, A., Bridgens, B. and Farmer, G.: Hygromorphic Materials for Sustainable Responsive Architecture, 2015.

Reyssat, E. and Mahadevan, L.: Hygromorphs: from pine cones to biomimetic bilayers, in J R Soc Interface 6 (2009).

Fratzl, P. and Barth, F.G.: Biomaterial systems for mechanosensing and actuation, in Nature 462 (2009).

Erb, R. M., Sander, J. S., Grisch, R., and Studart, A.R.: Self-shaping composites with programmable bio inspired microstructures, in Nature communications, 4 (2013) Timoshenko, S.: Analysis of bi-metal thermostats, in J. Opt. Soc. Am., 11 (1925) Skaar, C.: Wood-water relations, Springer-Verlag, London, 1925.

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Hoadley, R.B.: Understanding wood: a craftsman's guide to wood technology, Taunton press, Newtown, 2000.

United States Department of Agriculture (USDA): Wood handbook: wood as an engineering material, USDA–Forest Products Laboratory, Madison, 1999.

Dinwoodie, J. M.: Timber, its nature and behaviour, Taylor & Francis, London, 2000.

Wang, L., Toppinen, A. and Juslin, H.: Use of wood in green building: a study of expert perspectives from the UK, in Journal of Cleaner Production 65 (2014) Tsoumis, G.: Science and technology of wood: Structure, properties, utilization, Van Nostrand Reinhold, New York,1991.

Rijsdijk, J.F. and Laming, P.B.: Physical and related properties of 145 timbers: information for practice, Springer, Dordrecht, 1994.

Alben, S., Balakrisnan, B., and Smela, E.: Edge effects determine the direction of bilayer bending, in Nano letters 11 (2011) Meira Castro, A., Ribeiro, M., Santos, J., Meixedo, J.P., Silva, F.J., Fiúza, A., Dinis, M. and Alvim, M.R.:Sustainable waste recycling solution for the glass fibre reinforced polymer composite materials industry, in Construction and Building Materials 45 (2013), Andrei Gheorghe, Sen.Sc. Mag.arch. MArch (Harvard), Breathable Glass Façade.

Reichert, S., Menges, A., and Correa, D: Meteorosensitive architecture: Biomimetic building skins based on materially embedded and hygroscopically enabled responsiveness, in Computer-Aided Design (2014).

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9. List of figures

Figure 1 Jalli patterns ......................................................................................................... 23 Figure 2 Example of Mashrabiya (house of ahmad katkthudaal razzaz) .......................... 26 Figure 3 Jaali screen of tomb of Salim Chisti, Fatehpur Sikhri ........................................ 27 Figure 4 The perforated domes and roofs in Hebron – Palestine (above), Semi circular qamariya (below) ............................................................................................................... 28 Figure 5 Taqa patterns for window openings and facades ................................................. 29 Figure 6 figure showing solid void relationship ................................................................ 30 Figure 7 solid void ratios of different case studies. ........................................................... 31 Figure 8 dimensions of typical three cases ........................................................................ 32 Figure 9 image of glare renderings .................................................................................... 33 Figure 10 Park Hotel, Hyderabad – façade at night ........................................................... 35 Figure 11 How the form utilises the prevailing wind conditions....................................... 36 Figure 12 Building orientation is optimized to receive solar radiation at large angles and maximize view towards the lake on the east. ..................................................................... 38 Figure 13 Façade pattern detail ......................................................................................... 39 Figure 14 Manufacture of perforated screens using Laser press machines ...................... 39 Figure 15 façade installation details ................................................................................. 41 Figure 16 Al bahr tower .................................................................................................... 43 Figure 17 3D models of primary structure, façade and shading system ........................... 45 Figure 18 3D solar analysis on central portion of tower (Arup) ....................................... 46 Figure 19 View from the inside through the PTFE fabric. The supporting frame is a combination of aluminium and duplex stainless steel, to withstand the aggressive marine environment. ...................................................................................................................... 47 Figure 20 Installation of the Mashrabiya panels. The shape of the building in plan and elevation led to 22 different variations in the panel geometries ....................................... 48 Figure 21 Wind tunnel testing, 1:75 scale – pressure taps on open Mashrabiya panels ... 49 Figure 22 panels in different positions.............................................................................. 50 Figure 23 Reversible moisture-driven opening and closing of pine cones. ...................... 54 Figure 24 Principle of the response of hygromorphic composites based on differential hygroexpansion (i.e. shrinkage or swelling) of active and passive layers ......................... 54 74

Figure 25 The Bloom - A Temporary Installation at the Materials&Application Gallery, 1619 Silver Lake Blvd, Los Angeles, CA.......................................................................... 57 Figure 26 Climatic regions of India .................................................................................. 59 Figure 27 Sunpath diagram for Ernakulam, Kerala .......................................................... 60 Figure 28 Best orientations for existing plan forms.......................................................... 61 Figure 29 Showing movement of the sun with respect to building faรงade. ...................... 61 Figure 30 showing perimeter to area ratio ........................................................................ 62 Figure 31 design strategies................................................................................................ 62 Figure 32 Optimum solar shading..................................................................................... 63 Figure 33 Different types of shading devices ................................................................... 63 Figure 34 illustration showing schuco retrofitting system ................................................ 64 Figure 35 Figure showing the process of retrofitting a structure ...................................... 65 Figure 36 Variable Solar Protection Glass........................................................................ 66 Figure 37 image showing reflectance of variable solar protection glass .......................... 67 Figure 38 prototype in open and closed positions. ........................................................... 68 Figure 39 demonstrating the kinetic nature of the twisting glass facade .......................... 68 Figure 40 Simulated renderings showing effects of dichroic twisted glass faรงade. ......... 69

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