6.1 R G F : I M A P M G F R C 6

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171 CHAPTER 6-APROCESS MAP FOR GLASS FAÇADES RENOVATIONS

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HAPTER

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A PROCESS MAP FOR GLASS FAÇADES RENOVATIONS

“A great building must begin with the unmeasurable, must go

through measurable means when it is being designed and in the end must be unmeasurable”

Louis Kahn

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The design and construction process of glass façades intended for renovations involves complexities, which integrate different issues such as load-bearing structure, building services, building physics and, not least, architecture. There is a multitude of developments and requirements that demand new strategies for the future application of glass envelopes in renovation contexts.

The presented work has planned to carry out a literature research and a series of interviews with designers and experts in the field of glass façades and renovation projects. The aim of the investigation was to learn directly what are the main strategies that can be adopted and what are the main problematic aspects. The work has developed a map of the design and construction process for glass façade renovations and has collected an overview of the findings of the interviews as a basis for the development of support tools, to help the efficient storage, access and transfer of design information.

The quest for performing façades towards extreme transparency is required n renovation projects, in case of routine maintenance, change of use or ownership and to comply with new codes. Nowadays, the energy-efficient renovation of existing glass façades or the use of new glass façades to “wrap” existing buildings are key-issues to qualify and reuse our architectural heritage.

The themes related to energy saving and environmental sustainability in the construction sector are particularly problematic for professionals dealing with existing

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buildings, especially when buildings have a historic value:

 Which is the most appropriate approach to have when renovating existing envelopes?  How should a project balance the need to comply with regulatory standards and the

issue of conservation, reuse and renovation of architecture?

These topics emerge significantly if we consider the glass components of an existing façade, due to two different reasons:

1. Glass elements, especially if used in continuous curtain walls or in high wall to window ratio surfaces, determine significantly the performance of the entire envelope. Furthermore, it is relatively easier to increase the thermal performance of existing opaque components, by adding, for instance, one or more layers of insulating material, while it is very complex to improve the behaviour of transparent elements: then, it is extremely important to know and compare available technologies and innovative products.

2. Some categories of buildings belonging to modern and contemporary architecture (i.e. industrial buildings dating back to 19th-20th centuries, Modern architecture from the 1930s to International Style buildings) are mainly characterized by an extensive use of glass surfaces, that often perform poorly and increase the energy load: their improvement must always be balanced with restoration principles and must respect original architectural features.

In addition, the study and the use of glass façades develops into a regulatory framework that is still poorly defined and constantly evolving, regarding both design issues (i.e. lack of detailed standards and guidelines for glass structures; enactment of EPBD, Energy Performance of Buildings Directive of the EU, which involves the envelope performance), and requirements for building materials and systems (i.e. enactment of CPR, Construction Product Regulation, with the mandatory application of CE marking from 1 July 2013).

Due to the current technical improvements, the design issues and the standard requirements, dealing with glass façades is taking on a fundamental role during the design and construction process, both in case of new construction and in renovation projects (retrofitting and/or upgrading).

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Such trend suggests to study and carefully define the entire design process of glass façade renovations, to analyse the main issues related to the design, the engineering challenges and the possible future developments.

The aim of the research, that has been developed during a research period at the Glass and Façades Technology Research Group (gFT) based at the University of Cambridge under the supervision of Dr. Mauro Overend, was to collect data and information on existing design approach towards renovation projects with glass façades, in order to provide an overview on the design process, the related main issues and the best practices.

6.2 R

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ETHODOLOGY

The present work has first developed a map of the design and construction process for glass façade renovations. The map uses BuildingSMART’s adaptation of Business Process Map Notation and extends a map already developed for the construction of new façades [96]. Basically, the development of the draft version of the map was based on state-of-art and literature research [25].

Then, the map has been verified by 10 interviews with experts in UK (6) and in Italy (4). The interviewees were selected among architects, engineers, industry professionals, all of them with a strong experience of designing glass structures and/or of dealing with renovations projects (see Appendix A).

The interviews were carried out in person (except one that was mainly developed by e mail) and consisted of a 1-hour meeting. The interviewees were asked to comment on the map, to correct and eventually integrate it, talking freely of the topics they consider to be most relevant with respect to the subject matter. The interviewer had then prepared a series of questions to discuss with the stakeholders in order to deal with some specific issues during the course of the meetings. The questions were related to:

 Main features of glass façade design and construction process, especially for renovations,

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 Architectural issues,

 Design criteria for glass structures,

 Energy performances for glass façades and main design criteria

The map was used to identify the main of the renovation categories and the corner types of existing and future evaluations. Finally the collected data were used to develop the final version of the map. Three stages of the entire process map are analysed in further detail, namely:

(a) the assessment of the actual performance and

(b) the selection of renovation option and

(c) the preliminary project.

The research project also focuses on the use of glass systems in interventions on building heritage, with a critical examination of recent works. Some paradigmatic case-studies (Fig. 1) have been analysed and compared, from several viewpoints: building technology, structural and energy aspects, aesthetics and metaphysical values. The main aim is to capture the fundamental steps related to the design process for upgrading glass façades, especially by using novel technologies such as double skin façade (DSF) systems.

Fig. 1 Extension of the library of Eberswalde technical school (Herzog & De Meuron, 1997-98)

The work presents an overview of the findings of the interviews and is the basis for the development of support tools, to help the efficient storage, access and transfer of design information.

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6.3 W

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All the respondents confirmed that an increasing interest in glass façades in case of upgrading and retrofitting is detectable, since glass envelopes can be used in different building types, finding application in public buildings, banks, museums, commercial and residential buildings, and even in archaeological/historical sites.

The examples of renovation and reuse of abandoned buildings through a wide use of glass highlight how it allows the historical readability of a place. Nevertheless, glass construction, if used without understanding, can destroy space and architecture.

Modernizing buildings with new envelopes improves the value of a property. Thereby the operating costs are reduced. There is a wide range of improvements, mainly regarding:

 Energy efficiency,  Functionality,  Comfort,  Appearance.

Two of the respondents, who work in both the UK and the USA have shown that sometimes the projects of upgrading/retrofitting are imposed by local laws or by the insurance companies who have the management of commercial buildings in the City. Some American city councils require periodic inspections on the facades of skyscrapers: the New York City Department of Buildings has instituted Amendments to Local Law 11/98, the law that requires buildings taller than six stories to have their facades inspected every five years. Façade inspections must be conducted, witnessed, or supervised by "Qualified Exterior Wall Inspectors”.

Such interventions involve structural and performance improvements both for the opaque and the transparent envelope, which is often the weak point of the system. In addition, it should be noted that the major part of tall buildings is nowadays made with glass façades, using different technologies and finishes: therefore the retrofitting of glass elements in existing buildings is becoming more and more relevant.

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This strategy, which involves monitoring, inspections and checks on the building envelope, it is not yet widely used in Europe, but all the interviewees agreed that the trend in the coming years will be directed to this approach.

6.4 C

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Retrofitting existing building is often even more complex rather than designing new constructions, since the existing structure is part of the design constraints. Thereby, some compromises must be made both to meet standard requirements and to save historical appearance. On the basis of the data collected during the interviews, it is possible to make a division of the main categories of buildings that can be involved in retrofitting/upgrading operations using glass façades: architectural monuments, listed buildings, existing buildings with “minor” historical value (no listed buildings).

It is also important to underline that a wide use of glass in renovations shall be carefully assessed case-by-case, since glass, due to its qualities of transparency and its innate ability to create buildings from minimal visual impact, can be often adopted to integrate, partially or totally, gaps and entire portions of existing buildings.

Architectural monuments play a significant role for the identity and the history of a society; their energy performance is usually poor. Typically the categories of intervention allowed on this kind of buildings are only repair, restoration and replacement with elements of the same material and the same sized, both as regards the glazing and the frame. Thereby, the energetic renovation will be taken behind the heritage protection. The energetic improvement shall be always compared to the baseline case, i.e. the existing performance.

Some of the most important interventions in this context, which have treated glass façades as real monumental elements, concerned iconic buildings for modern and contemporary architecture, such as Faguswerk in Alfeld, Bauhaus building in Dessau (Fig. 2 a, b), Schillerpark in Berlin: all of them are listed in UNESCO World Cultural Heritage.

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Fig. 2 a, b. Bauhaus in Dessau, after renovation.

Existing building with “minor” historical value usually belong to a large part of real estate in Europe, that is not monumental, but old and aesthetically appreciated, too expensive to demolish or to adapt to the new regulations.

Thereby, in order to reduce energy consumption and CO2 emissions, a large part of buildings from the 1950s and 1970s are being now refurbished. They usually do not comply with the stricter standard building regulations introduced in recent decades and therefore they often need to be renovated not only in terms of energy efficiency, but also to improve serviceability and robustness.

More than half of the respondents had to deal with an intervention of this type of buildings, both residential and commercial facilities. They all confirmed that the renewal of an existing building has a creative potential and allows to present a new modern appearance to the façade and, at the same time, to optimise the building’s energy efficiency.

In some cases, especially in retail department, commercial and office buildings, the interviewees have been requested by the client to use a glass façade for aesthetic purpose only, in order to give new expression to their corporate image, improve communication and facilitate the rental of the building.

Work on buildings that are listed by the Architectural Heritage, but not considered as monuments, represent an intermediate category as the constraints do not affect the integrity of the façade as a whole. Regarding this category, there are several design approaches, which vary case-by-case, but generally it is possible to replace the glass elements and frames with new materials and façade systems.

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6.5 C

ATEGORIES OF

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ORK

The analysis of the different case-studies proposed by the respondents allow us to identify three main classes of intervention on glass façades, which can vary as a function of the building category. These classes consist of selective reconstruction, recladding and over cladding.

In a selective reconstruction only those members of the glass façade that are defective would be removed and replaced with elements that are identical or similar. Examples would be the selective replacement of corroded portion of steel frames, reglazing of existing frames or the local repair of sealants and gaskets.

Recladding is the removal of an existing exterior system and replacing it with a new

system. Typical reasons for recladding include water/moisture damage, general upgrade or replacement of improperly installed systems. The overall recladding of a glass façade can imply the use of high-performance glasses, that can significantly improve the comfort inside the building and the performance of the envelope.

The recladding option has become quite popular with the 1950-s skyscrapers because it allows the owner to complete update the image of the building as well as install a state-of-the-art curtain wall that will perform in a superior manner if compared with the original curtain walls. This option, however, is bound to become more controversial as a building becomes listed or landmarked.

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The concept of over cladding (Fig. 3 a, b) is now well established as a means of regenerating older buildings. With the over cladding the original wall system is left in place and is clad with a new curtain wall system: nowadays glass façade systems are used widely to over clad, because of their versatility, the ability to integrate in any context and to fit in with different architectural styles and materials. New over cladding can serve to restrain and protect the existing façade such that the regenerated buildings life expectancy is comparable to that of a new building.

Experts confirmed during interviews that warranties are available to cover both the existing structure/facade and the new over cladding as they are mutually dependent upon one another for performance and longevity. A wide variety of cladding solutions exist that offer an equally wide variety of life expectancies, performance and aesthetic properties.

To refurbish, meeting only minimum standards, extending the buildings life short term for say 20 years is to pass our inherited problem to the next generation. Quality, long term, 60 year life systems exist that can readily surpass current standards by 50% for additional capital expenditure of circa 15% over the cheapest solution. An example of over cladding is the renovation of “Bergognone 53” complex in Milan, Italy, as a result of an international competition by real estate developers, Hines (Fig. 4 a, b).

The former Postal Service building is located in a former industrial area and complete urban block, four building with an inner court built in the 1960’s and 70’s. Renovation preserved the existing internal space, whilst updating the design of the building for new functions.

The before and after renovation images of this building are shown in figures 3 a, b. The new transparent outer skin follows the modular structural frame of the block. The more exposed south-west side has a “second skin” projecting 600 mm that acts as a large sun blind or passive filter. This second layer reduces solar radiation, thereby lowering air-conditioning energy requirements. “Chilled” ceiling beams, partly behind perforated suspended ceilings, are connected to the ventilation system and to part of the lighting circuit. The internal courtyard was completely refurbished using a structure of suspended steel and glass. The architectural model’s overall energy consumption requirement has been

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calculated at 145 kW/m2, which represents up to 50% energy reduction. A similar façade in a standard cladding material would lead to 280 kW/m2 energy consumption.

Feasibility assessment must be accurate and comprehensive to allow the informed decision-making process to work effectively. The interviewees stated that past project examples of most cladding and window options are available up to 20 years old: they can be examined and reported upon such that the industry learns and progresses, improving efficiency. Over cladding will normally have an impact on the appearance of the building.

During the interviews, it was found that one of the main issue related to the process of redesigning existing glazed façades is the connection of the new façade supporting elements to the existing structure of the building: most of the interviewees (80%) underlined that the assessment of the characteristics of existing structures and materials is crucial to design joints and anchors able to resist to additional loads.

The renovation of a façade can also be wired entirely from the outside, whilst the building is still in use. Manufactures has developed systems and high-efficient components that can be installed keeping the building in operation; this means that the underperforming existing windows on the inside can be removed efficiently and to a precise deadline.

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6.6 D

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In other industry sectors, such as ship industry or product design, process mapping has been successfully used to manage complex processes [97]. The main benefits of process mapping suggested by literature include increasing understanding of actor’s roles and activities (Klotz et al. 2008), and aiding identification of strategic, process and IT requirements [81], or forming the basis for IT systems [94]. A process map, also known as a flow chart, is a useful organizational tool that can improve the transparency and the level of communication among the different stakeholders involved during the development of the process [96].

In the context of the façade industry, the application of this methodology has been limited to a specific type of façade or to a part of the construction process. The works of reference are the map for the precast cladding process, developed by Karhu [48] for the purpose of developing a product data model using the IDEF0 modelling method; Gray and Al-Bizri (2007) proposed a knowledge-based-engineering (KBE) model representation of design processes and illustrated the concept with a map of precast cladding panel design [96].

Within the project CIMclad, Agbasi has modelled the supply chain processes for a rainscreen cladding, using the IDEF0 methodology [10]. This work, carried out from the point of view of the façade engineer, illustrates the whole life cycle of a specific product, starting from the design to the production, marketing, procurement, and installation. The process presents a high level of detail, but only focuses on a specific single type of rainscreen and thus lacks of generality.

Fazio et al.’s work [80] considers the application of BIM technology to building envelope design. The International Foundation Class (IFC) schema is used to store and transfer design information in a system that incorporates a database of bench mark values of façade performance. The system evaluates design alternatives, partly based on the values stored in the knowledge database. The work only considers thermal and environmental design requirements.

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The process map developed at the University of Cambridge from Voss and Overend [96] took as its basis the Agbasi’s approach described above, but the map aims at covering all types of cladding, using the Business Process Map (BPM) notation, recommended by BuildingSMART.

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The aim of the mapping project developed at the gFT, University of Cambridge, is to produce an “as-is” representation of the current process of façade design and construction. It proposes to improve communication between construction industry domains, improving the process of designing, construction and operation of façades. The top level map shows the entire process, identifying the key-stages and the main actors that are involved through. Each sub-activity is then illustrated in further detail: the expansion includes details of the information used and produced in each sub-activity.

The map uses the knowledge-based engineering (KBE), that represents the technological application of the strategy of Knowledge Management, relative to engineering. The KBE provides designers with the tools to capture and reuse the multidisciplinary knowledge in an integrated manner in order to reduce time and cost of design, as a support toll in the development of concept design. The KBE provides designers with the tools to access their ideas in a virtual way, shaping the product, modifying the geometry and supporting the investigation of various "what-if" scenarios in the design.

The notation is based on IFC (industrial foundation classes), that are an international open specification designed for the exchange of building information in the construction industry. The IFC schema provides an object model based description of spatial elements, building elements, MEP elements and other components. BuildingSMART (former IAI – Alliance for Interoperability) coordinates the development of the IFC data model schema. is an initiative of BuildingSMART International (bSI) promotes the use of OPEN BIM using the open BuildingSMART Data Model.

BPMN (Business Process Modeling Notation) creates an important link between the design of the business process and the realization of the process itself. BPMN has been

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developed with a very solid mathematical basis so that product is a language implementing precise.

Fig. 5 Business Process Modeling Notation (BPMN).

The result is BPMN Business Process Diagram (BPD), which shows the flow of activity based on a standard graphical notation (Fig. 5). The advantages of BPMN are the following:

 Processes are organized by intuitive notation (flow chart);

 Standard notation improves communicability inside and outside the company;  Language constructs to execute a software are represented in a simple way.

The implementation of the system aims at developing a support tool configuration using open source BIM technology (Fig.6) .

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6.6.3 E

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Modern glass façade projects involve a wide range of disciplines and materials, that shall be carefully assessed since the early stages of design process to achieve an optimal outcome; moreover, renovations present further constraints and complexities, involving geometry, structural and thermal issues, aesthetics. In particular, modern and contemporary renovations for buildings in which glass façades play a fundamental role have to cope with different issue: the need to repair and prevent from degradation, the norm and code compliance, the preservation of key-architectural features.

The main task is to enhance a process mapping for glass façades renovations; first, different kinds of works are divided into classes, that require specific design approaches (local repair and general conservation; replacement of the entire facade with similar frames or with a totally new cladding system; construction of an additional glass facade). Then, a process map describing renovation projects for existing glass envelopes is developed and verified; as a demonstration, the process is validated for real-world façade projects, and the validation consists of the following steps:

 A simplified process map is produced for use in interviews with selected industry experts.

 The industry representatives are asked to work through the process maps, step by step, adding information and making corrections.

 The first version of the map is then reviewed and the corrections are incorporated, using the BPMN-BuildingSMART notation.

The development of the process mapping has showed that one of the main issue when dealing with an existing envelope is to assess how it is actually performing now. The evaluation of existing performances shall be deduced by monitoring and in-situ tests, concerning thermal and structural behaviour.

The number and the types of monitoring shall be defined in the early steps of design, to undertake useful surveys and obtain the information for the baseline benchmark: this is the basis to develop technical solutions and to compare different options. Moreover, the analysis of case-studies revealed that two of the main problems related to glass renovations

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concern safety and energy improvement/enhancement of internal comfort; these issues should be discussed and included in the design of the entire building from the very beginning: too often the façade design is carried out when fundamental decisions, for instance pertaining to the HVAC system, have already been taken; at this point it can be too late to benefit fully of advanced façade solutions.

There is a pronounced need for a understandable design process and a common language in order to characterise and communicate the performance of innovative systems; for instance, quantities such as U-value and solar factor are not readily applicable when the envelope interacts with the ventilation system, and traditional ways of designing HVAC systems may not be adequate when assessing possible application of innovative solutions.

Retrofitting existing façades is very often more complex than designing new ones as the remaining structure has to be included in the design concept and in many case compromises have to be carried out to meet standard requirements.

Furthermore, the problem of renovating glass façades shall not be intended only by an energy and technical performance point of view, but it must also be seen in terms of the more general theme of conservation and reuse of architectural heritage, especially for listed buildings: the external skin defines the unique identity of a building, and its image must be preserved.

All these considerations, deduced from the case studies and by interviewing designers, should not be evaluated only qualitatively, but also be included in a process diagram able to explain clearly what are the steps to be taken during the design, construction and maintenance phases, who are the professionals involved and what are the timelines, since only a comprehensive and integrated approach can produce a performing and balanced outcome.

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6.7 R

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One of the main methodological issues related to the reuse of modern and contemporary architectures lies first in their conservation, since some of them were designed to be temporary or otherwise of limited duration: rationalist architects, for instance, contemplated the aging and the following replacement of their works within 40-50 years. The need for conservation, however, also stems from the way we “perceive” a building: if we recognize in it a "material witness having the force of civilization" (Franceschini Commission, 1964), we will keep it regardless of the original concept [20].

After that, a further problem regards the attitude to adopt towards the original architectural elements (frames, mullions, transoms, etc.) that are in poor condition and shall be locally repaired or even substituted: some can be still manufactured but a large part of them are now unavailable; furthermore, other products or technological solutions have proven to be unsuitable and do not provide internal comfort and protection against moisture and weathering. A common feature of modern architecture, for instance, was the use of windows frames with thin steel or aluminium profile and single glazing panes: this technological system suffers from a several problems of damage and degradation and cannot ensure adequate levels of comfort.

The attitude towards renovating glass envelopes, from the repair and conservation tout court to the complete replacement of existing elements, shall be always balanced case-by-case in order to find solutions that can improve the performance of the façade and, at the same time, save both the material features and the architectural image of the building. In Europe, the cultural and technical debate has been gradually recognized the unique value of buildings belonging to modern and contemporary architecture; furthermore this appreciation affects not only single paradigmatic examples, but also concerns about common types of buildings, that were previously considered of secondary importance [11], such as industrial buildings.

The concept of architectural heritage has been then extended, as the awareness of its intrinsic fragility, since the timing of obsolescence are significantly shorter than the pre-modern works, and modifications or replacements of elements and materials can cause the

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loss of relevant features [20]. The deep knowledge and the critical evaluation of intrinsic cultural qualities of modern and contemporary architectural heritage is therefore fundamental to choose what should be preserved and what can instead be replaced to meet the new code requirements [43].

6.8 C

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The complex variety of approaches to renovate and upgrade existing glass envelopes can be illustrated by the analysis of some case-studies, which embody different philosophies regarding renovation attitudes (maintenance of the existing façade and local repair, complete or partial replacement of the elements, introduction of new building components) and identify a number of specific technical solutions.

Case studies can provide significant value to the user, by documenting project in a manner that presents experience based upon completed works [43]. Examples of case study subject matter focuses on, in the present work, a specified architectural element or building system, such as curtain wall or structural glass facade. The content can include various aspects of concept, programmatic content, structural design, building form or technology, materials and processes, and detail design. The documentation of some performance aspect of the project, such as thermal, daylighting or acoustic, shall be outlined.

Three renovation projects are described: the first regards a building characterized by an unique cultural and technological value; the second renovation project investigates what is the design approach to a former industrial plant, now converted to an office building. The analysis of the following case studies shows the creative potential but also the complexities that lie in the renewal of older buildings, especially related to the detailing and the structural complexity of designing the new façades.

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EINE

Faguswerk (Fig. 11 a, b), designed by Walter Gropius in 1911, adopted for the first time cutting-edge technologies imported from the U.S.A. and still maintain an innovative

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language. The building facility, and in particular the building for offices and the engine technical room, presents new solutions obtained by the use of glass: large glass surfaces and thin steel frames provide transparency to the envelope, since the brick pillars are set back from the glass wall, anticipating the construction system of curtain wall [52]. The angle of the building is "empty" and inside the perimeter of the building there is a sort of “glass cage”. Such solution was then performed at the Bauhaus buildings in Dessau, designed always by Gropius [101].

Fig. 11 a, b. Faguswerk in the '20s.

In Faguswerk, the glass façades, with vertical pattern, rise up to three storeys and are divided according to a modular grid with variable dimensions (width = 110.8 to 116.6 cm, height = 55.5 to 59.5 cm). On each floor there are modules made of transparent single 6/4 glazing of the Rhineland, operable or fixed, with steel and metal panels corresponding to the slab floor. The glass façades were carried out in two phases of construction: such difference will be a matter of debate during the restoration project. In the first phase, Gropius opted for standard steel profiles, already available on the market, characterized by load- bearing mullions and transom openings, wasistas type. In the second phase, the architect use special profiles, made ad hoc, with rounded corners, grooves and vertical centre-pivot opening systems. Since the early '30s, the Faguswerk highlighted the fragility typical of modern buildings, which are often compounded by an advanced state of decay, due to the experimental nature of many finishes and the attitude of many elements, including frames and gaskets, to ensure a limited duration. Around the mid-80s, the problem of restoration of Faguswerk was the subject of a lively debate involving Jörn Behnsen, the architect

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commissioned by the owners of the factory, and the Museum of Architecture in Frankfurt [22]. In addition to the need of defining the future use of the buildings, for which Behnsen wanted to keep the production function as a tool for preservation of the buildings, the criteria for restoration were the subject of extensive discussion: Faguswerk was perceived to be taken a paradigm, a sort of "monument" of modern architecture [52].

The construction systems in Faguswerk presented numerous problems connected to the use: the advanced deterioration of the façade involved rupture of several glass plates, lack of tightness of seals and gaskets, and deformation of the steel profiles, which were significantly undersized compared to wind load, thermal expansion and glass self-weight, due to have displacements and deformations up to 5 cm.

In addition, the supporting structure had an advanced state of decay, and was not able of complying with current code requirements. The energy performance of the envelope showed discomfort for internal environment and significant energy losses: the single glass panes, used for large areas, the lack of insulation and solar protection systems, lead to unacceptable temperatures in both winter and summertime, while the deformation of the frames prevented the water and air tightness of windows and doors.

Initially the Building Heritage and by Behnsen adopted very far approaches of restoration: while the Building Heritage asked for a local repair of the façade elements, with the preservation, if possible, of the original "materials", Behnsen suggested to rebuild the 22-span glass façade "à l 'identique ", through the use of elements similar to the existing design, but with a higher thickness of the frame [22].

After a long debate between owners, designers and Building Heritage, due to the high level of damage of the existing components a position of mediation was finally reached. Different "degrees" of intervention (Fig. 12 a, b, c) were defined, from preservation to recladding.The criteria of selection was linked not only to the level of decay, but also to the future internal use: for instance, the portions of the façade that correspond to occasionally occupied rooms, are mainly preserved; the glass envelope in the stairwells does not fully comply with thermal standard requirements. Viceversa, office facilities are provided with new façade systems. Such replacements do not make distinction between the first and the

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second phase of construction, and consist in the use of steel frames similar to the original as regards the external thickness, that have internal profiles with appropriate thermal-break structure and thermally insulating glazing, in order to ensure a constant climate wellbeing.

Fig. 12 a, b, c. Facade details.

6.8.1 R

ESTORATION OF

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VREA

The ICO Central plant (Industries Camillo Olivetti) of Ivrea (Italy), designed by Luigi Figini and Gino Pollini between 1938 and 1949 and now head office of an important call centre of a telephone company (Fig. 11 a, b), has been completely restored by architects Dante O. Benini and Enrico Giacopelli, during 2005-09 [44].

The building is one of the most significant Italian architectural examples of the early 20th century and its most distinctive architectural feature is definitely the large continuous glass façade on the main elevation and in the courtyard (Fig. 13): it became, since its creation, the "advertising" image of the company, highlighting the intention brought by both the designers and the owner towards instances of modernity and social progress [69].

The renovation of the impressive façade, consisting of double skin glass envelope, led to various intervention strategies, since the advanced state of decay and the inadequacy of existing systems (frames, glazing, gaskets, putty etc.) denied the possibility to repair the local lacks [64].

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Fig. 13 ICO Centrale, Ivrea, 1937-42- The stairwell and the façade in the internal courtyard.

Two different renovating strategies have been carried out: for the two longitudinal main elevations, the outer layer of the façade, consisting of a total of 2,300 m2, where locally restored, while the interior skin was completely replaced with a new one (Fig. 14 a, b): the thermal break aluminium frames and insulating glass units with low-emissivity coating are able to satisfy regulatory requirements and internal well-being (Fig. 15 a, b).

Fig. 14 a, b. ICO main elevation before (left) and after renovation (right)

On the other hand, completely new glazed curtain walls were used for secondary elevations, respecting the existing architectural constraints. The new glass envelopes, which extends for a total of over 5,700 m2, have been designed according to the sizes and the aesthetic characteristics of the original façade; the design team has developed, together with the manufacturer, an ad hoc system of profiles and glazing panes to accomplish with

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the structural and thermal constraints and to ensure greater durability [44].

Fig. 15 a, b, Detail of the facade before (left) and after (right) requalification (Courtesy of arch. Enrico Giacopelli).

6.8.2 R

EUSE OF AN INDUSTRIAL BUILDING

(G

UNA

B

UILDING

)

OF THE

‘50

S

,

M

ILAN

As previously analysed, the use of glass for renovation projects can meet different criteria, from the complete conservation of existing features and materials, to the partial or total replacement of the transparent components: the design process depends on whether we are favouring the maintenance of the original elements that characterize the façade or whether instead we choose to significantly improve the performance of the envelope, while maintaining a mimesis with the shapes and dimensional features of the original.

However, there is another design attitude, that uses innovative glass surfaces to "exhibit" the characteristics of modernity [59]; these technological solutions aim to improve the qualities of the envelope and can be pursued especially in the renovation of buildings belonging to a diffuse and less valuable heritage, such as industrial construction and production plants, where constraints are less stringent [54].

A significant example is the reuse of a former industrial building in the ‘50s in Milan (Italy), that was completely renovated in 2007 to become the new headquarters of

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pharmaceutical laboratories Guna, under the direction of Polis Engineering (Fig. 16 a, b). The specific theme of the project involved the construction of a new glass façade on the main elevation, that provides a new representative and symbolic image to the building, as well as improving the overall functioning: the existing underperforming masonry wall has been covered by a second "skin", at a distance of about 25 cm, made of a double IGU; the cavity space is ventilated naturally and significantly contributes to the climate of interior offices in both summer and winter conditions [71].

Fig. 16 a, b. GUNA building main elevation before (left) and after (right) renovation.

The steel bearing structure consists of an anodized aluminium system of mullions and transoms, produced by extrusion and 55 mm thick; to reduce or eliminate thermal bridges, several PVC slats are inserted between the inner and the external side of the aluminium profiles, while laminated glass panels are assembled in insulated glass units, with external tempered glass pane 8 mm thick, air cavity of 16 mm and inner tempered pane of opaque glass, 6 mm thick.

The thermal analysis underlined the positive effect of slats: the high reflective shading devices allow a sufficient amount of solar gain for the indoor space in heating season and a considerable load reduction in summer. Glass panels are about 2,500 rectangular elements of different sizes (Fig. 17) and are arranged randomly to give more dynamism to the façade. In this case the transparency of the glass is modulated in a variable manner to obtain different shades and to hide the existing structural type, while achieving excellent performance characteristics (Fig. 18).

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Fig. 17 Detail of the façade Fig. 18 Internal view

6.9 I

NTEGRATED

D

ESIGN

P

ROCESS

F

OR

G

LASS

F

AÇADE

R

ENOVATIONS

The design and construction process of glass façades intended for renovations involves complexities, such as geometry, aesthetics, structural and thermal issues, that are often difficult to manage during the whole development of a project. In some respects, a key factor in the problems of the broader construction industry is its fragmentation and its poor level of communication among different working methods [10].

The analysis of real-world façade projects for renovations and the research carried out through interviews with experts have demonstrated that incorporating project constraints at the early stages of design can improve significantly the whole design development. Modern and contemporary renovations for buildings in which glass façades play a fundamental role have to cope with different issues:

 the need to repair and prevent from degradation.  the preservation of key-architectural features.  the code compliance.

 the increasing need of certification and rating systems (such as LEED, BREEAM e Green Star).

The conflict between both issues, energetic renovations and sensitive handling with historical monuments, leads to new design approach. The design and construction process for renovating glass façades require a complex and multi-objective approach, not only for “iconic” buildings, but also for existing structures with minor historic value: this debated

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topic often comes up against with the needs to replace an underperforming façade and the requirements to improve the occupants well-being.

The different steps of the design construction process for glass façades in renovation projects has been deeply discussed during the 10 interviews. The focus was mainly on the early stages of design, since they seem to be, according to the interviewees, the fundamental and crucial moment for the future development of the project.

The interviews with the general designers (architects, engineers) have shown that often they lack of the basic knowledge to understand, in the early stages of project design, what are the technological solutions and the products available, and what could be, in broad terms, the impact of such choices on the performance the façade. On the other hand, the façade consultants highlight that their role “engineering” becomes extremely complicated if there is an initial inconsistency, for example, on the structural level.

The information collected during the interviews leads us to reflect once again that one of the key-criteria for the success of glass façade renovations lies in the organisational structure of the design process.