Sustainable building envelopes

Dr. Winfried Heusler, Senior Vice President Engineering, Schüco International KG, Bielefeld/GER

Summary

Around the globe, more and more certification systems for sustainable buildings have been appearing in recent years. Obtaining a certificate of this type by means of practical, affordable building envelopes requires a holistic planning process, implemented with technically mature, well-engineered products. Using the building envelope to efficiently save and generate energy plays an essential part in this process. If the aim is to improve the ecological, economic and socio-cultural impact of the building envelope throughout the building’s entire lifecycle, functional optimization alone will not suffice: fabrication, assembly, maintenance and disassembly must be taken into account as well. In this context, windows and façades fabricated on a construction kit basis are particularly apt. As a system supplier, Schüco assumes responsibility for developing and managing the generic construction component kit as well as special project-specific building components (which, however, should be based on the basic kit and be as compatible as possible).

1. Introduction

Sustainable building envelopes are an integral component of sustainable, climate-compatible buildings within a context, hopefully, of sustainable urban and rural planning (Fig. 1). The envelope has a huge influence on a building’s usefulness and longevity, protecting persons and property within it as well as helping to determine the level of interior comfort. Moreover, the energy-saving and energy-generating qualities of a building envelope are critical in determining the scope and even necessity of a building’s technical infrastructure. Nor is this merely a matter of initial investment and operating costs: at issue are primary energy consumption and the emission of pollutants for decades to come. Depending on the building’s location, basic structure and intended use, building envelopes offer more or less major potential for the thermal and electrical exploitation of solar energy. The higher the price of energy, the greater the impact of energy-saving and energy-generating features in the building envelope on the building’s profitability and market value will be. Present trends notwithstanding, the growing scarcity of natural resources will dominate future developments. Particularly when it comes to renovation work, much can be achieved with regard to operating costs and environmental protection at comparatively little expense, since earlier, often highly antiquated, technical concepts generally fall far short of current standards. Cost effectiveness increases when an improvement in the building’s external appearance is accompanied by a simultaneous enhancement in ease of operation and interior comfort. Thus, when conceiving and planning a building envelope, it is important to take the building’s complete lifecycle into account, starting with the raw materials and construction materials necessary for erecting it, followed by the manufacture and assembly of the individual building components, subsequent operation of the building including cleaning, maintenance and repairs, and culminating in the renovation and/or demolition of the building, including possible recycling of the building materials. When striving to minimize energy consumption and costs, it is of course important not to neglect interior comfort.

2. Sustainability

In 1972, thus even before the oil crisis (1973), the first report of the “Club of Rome”, entitled The Limits of Growth, appeared. It sought to provide a more profound understanding of the interplay of the political, cultural, economic and ecological variables. The dynamics of world growth were modeled, taking into account the factors of population density, food resources, energy, raw materials and capital as well as environmental pollution and land use. This report is considered the “granddaddy” of sustainable development studies. In the same year, the UN conference on the Human Environment took place in Stockholm. The representatives of 112 countries undertook for the first time to engage in cross-border cooperation to protect the environment. In 1979, the first World Climate Conference took place in Geneva. Attended by numerous scientists, debate centered on a possible connection between human activities and climate anomalies since 1972. The World Commission on Environment and Development (WCED), set up in 1983, published its the final report in 1987, Our Common Future, also known as the “Brundtland Report”. It addresses the overall concept of sustainable development, defining it for the first time in modern terms still applicable to this day:

• “In sustainable development, economic life, ecology and social aspects exist in harmony.”
• “Sustainable development meets the needs of the present without compromising the ability of future generations to meet their own needs”.

During the following decade, steadily increasing knowledge of global climate change led to growing interest in the issue of sustainability in more and more countries. The parties to the Kyoto Protocol Climate Conference, signed December 11, 1997, undertook to reduce emissions of six greenhouse gasses by 2012 to 5 percent below the 1990 level. Exactly ten years later (December 3-14, 2007), the UN Climate Conference in Bali triggered a series of international conferences at which a successor treaty to the Kyoto Protocol (which expires in 2012) was supposed to be agreed by December 2009.

In the meantime, industrial standards committees have also turned their attention to the issue of sustainability. In May 2008, for example, ISO 15392 “Sustainability in Building Construction – General Principles” was published, laying the groundwork for sustainable growth in the construction sector and establishing standards of quality and functionality. Not only does it minimize the negative impact on the environment, it also results in economic and social improvements at local, regional and global level.

In a parallel development, the number of certification systems for sustainable building has been proliferating worldwide since the 1990s (Fig. 3). The umbrella group “World Green Building Council” already encompasses more than ten member organizations. Among the best-known certification systems are the LEED in the United States and BREEAM in the UK. The “German Seal of Approval for Sustainable Construction” is a joint program of the German Association for Sustainable Building (DGNB) and the German Federal Ministry for Construction, Transport and Urban Development.

For building owners and building users, sustainability certificates provide proof that sustainability criteria were taken into account when planning and executing a building project, demonstrating adherence to the objectives of sustainable construction. The use of sustainability certificates is voluntary. Since the certificate serves as a symbol of quality, for the investor sustainability it becomes something transparent, measurable and marketable. It is thus safe to assume that more and more investors will seek certification of their buildings. As a rule, environmental quality is the prime concern when evaluating “green” buildings. In the case of sustainable buildings, evaluation goes beyond ecology, taking into account a building’s economic, socio-cultural, functional and technical quality. Its entire lifecycle is analyzed, starting with the raw materials and construction materials necessary for erecting the building; the manufacture and assembly of the individual building components; subsequent operation of the building including upkeep, maintenance and repairs; and, ultimately, the renovation or demolition of the building, including the possible recycling of building materials (Fig. 4).

When looking at the economic aspects, it is first and foremost the investment costs that are considered. These comprise the planning, material, fabrication, assembly and commissioning costs. The notion of what constitutes the value of real estate today is changing: an isolated consideration of the investment costs no longer suffices. When taking the long view, the costs of using the building, i.e. the operating and maintenance costs, come to the fore. The operating costs include the energy costs for climate control and lighting (heating, air-conditioning and electricity) as well as operating costs for custodial services and maintenance (inspection, upkeep and repairs). But the building’s economic value also depends on its ecological, socio-cultural, functional and technical quality. For example, sustainable buildings contribute to a positive image and greater acceptance from user and occupants, assuring high occupancy rates and thus strong value retention in the long term.

In this context, “ecology” means husbanding resources and protecting the natural environment. In particular, the focus is on primary energy and water requirements as well CO₂ emissions, pollutants and high-risk materials. In evaluating building and façade concepts, it is important to remember that, particularly when it comes to measures for reducing subsequent energy consumption, saving resources requires short amortization periods. Saving energy is a particularly tangible means of protecting the environment, since some 40 percent  of CO₂ emissions come from supplying buildings with energy!

By establishing guidelines for the total energy efficiency of buildings for the member states of the European Union, Directive 2002/91/EG of the European Parliament and the Council of Europe stipulates the passage of laws and regulations to improve the energy efficiency of buildings.

In Germany, this resulted in the amended in Energy Saving Regulation, which came into force in October 2007 (Fig. 5), and is to be amended again at the beginning of 2009. It stipulates that energy requirements for non-residential buildings be determined in accordance with DIN 18599 not only for heating but also for artificial light, mechanical ventilation and air conditioning. This encourages energy-efficient construction which aims to minimize the negative impact on the local climate by using as few resources and as little energy as possible, while at the same time making maximum use of the positive effects of the sun, daylight and wind. In tandem with the steady evolution of this regulation, for a number of years the German government has sponsored numerous demo projects for energy-optimized homebuilding, e.g. “solar houses”, “low-energy houses”, “3-liter houses”, “zero-heating energy houses” and “plus energy houses” (Fig. 6). Among the population at large, this has given rise not merely to heightened energy consciousness, but unfortunately to a certain measure of confusion as well due to the coining of neologisms such as “passive house”, “eco-house”, “zero-energy house”, “zero-emissions house”, “net zero-emissions house”, “energy-autarkic house” as well as “KFW-60” and “KFW-40” houses.

Any serious compilation of comprehensive lifecycle evaluations (“eco accounts”) for construction products has to take into account not only the manufacturing and utilization phase, but also reutilization and/or disposal. The German industrial standards DIN EN ISO 14040 and DIN EN ISO 14044 specify the sequence and elements for eco accounts. The ISO 14000 series of standards – and especially the ISO 14020 series – regulate the generation and use of environmental information. Thus, ecologically rational results are only obtainable when disassembly-friendly construction takes place using environmentally sustainable fabrication and assembly techniques combined with the economical use of resources. In the process, packaging and transport requirements should also be kept to a minimum.

The socio-cultural aspects encompass a building’s exterior and interior perspectives alike. Along with the building’s form and aesthetics, of decisive importance here are its interior comfort and ease of operation as well as domestic and workplace health. At least in office and administrative buildings, the importance of these criteria will grow in the future as the public becomes increasingly aware that a comfortable temperature, fresh air, the use of daylight, and acoustic comfort have a direct bearing on worker performance and absenteeism. DIN EN 15251 “Input Parameters for Indoor Climate in the Design and Evaluation of the Energy Efficiency of Buildings – Indoor Air Quality, Temperature, Light and Acoustics” offers recommendations for presenting parameters of the indoor climate in connection with energy aspects, and defines for the first time the permissible temperatures for buildings without mechanical air conditioning. This standard also stipulates the necessary ventilation rates (external air volume flow), factoring in the number of persons and the building’s emissions. However, the diverse techniques for evaluating comfort documented in these standards are not always practical or even available. It should also be noted that any modernization of a building’s energy infrastructure must be visible to the user and result in an enhancement of the building’s outward appearance. Just changing the sealings, fittings and windowpanes makes no sense if the window profiles – which may be showing their age – are left unchanged and in plain view.

3. Ways of increasing energy efficiency

The energy a building consumes during its entire lifecycle is obviously a key aspect of sustainable construction. In the course of minimizing energy consumption, which normally focuses on the utilization phase, it is important not to neglect the creative qualities of the building envelope – or a comfortable interior (Fig. 7).

Viewed in a traditional, simplistic way, energy saving is tantamount to a deterioration in interior comfort. In fact, by analyzing certain exemplary projects, it quickly becomes clear that various degrees of comfort can be obtained with the same level of energy consumption: it depends on the concept; and it depends on how the building is operated. (Fig. 8).

Poor concepts result in unacceptable interior comfort despite enormous levels of energy consumption. The same applies to “suboptimal” ways of operating. In the late 1990s, research into the “sick building syndrome” brought many negative examples to light, and not only in old buildings. A genuinely energy-efficient building is characterized by low energy requirements and a high degree of interior comfort. Accordingly, the key thing is to decouple interior comfort from energy consumption. In a systematic extension of the simple principle expounded by Gertis and Hauser, “First adapt the building to the climate, then adapt the air conditioning to the building”, three consecutive optimization steps present themselves.

In a first optimization step, suitable concepts and the resulting components are used to enhance comfort at the same time as reducing energy requirements (Fig. 9).

This is especially successful when the period extends in which a building’s interior can be kept comfortable without the need for outside sources of energy. Special building envelopes are helpful here: on the one hand, they reduce the longer-term differences between the local outdoor climate and the comfortable indoor climate (i.e. by minimizing the outside climate’s impact on the building’s interior); and on the other, by mitigating or smoothing short-term oscillations in the weather (i.e. limiting extreme values). A building’s energy efficiency can be increased still further when the building envelope acts as a semi-permeable membrane. This not only reduces negative external influences, but also exploits positive external influences to the maximum extent possible, taking advantage of natural heating, cooling, light and ventilation. The building envelope thus reacts dynamically to changing external and internal parameters, offering the right measure of permeability at the right moment to let in sun, light and air. In this context, a return to the working methods of traditional builders would appear to make sense, who would take into account the challenges and possibilities of the local climate as well as the habits, skills, cultural peculiarities and needs of the population. Today’s methods of utilization, however, result in complex, sophisticated parameters that necessarily pose different requirements.

This becomes instantly apparent when comparing office and administration buildings with residential properties. And what does it look like at first, when the building is a hotel or hospital, a cultural, scientific or educational facility, a shopping mall, leisure park or convention centre, airport or train station? Fundamentally, sustainable building envelopes need to be designed differently for different climate zones and different uses in order to take full advantage of the benefits and avoid problems. It should be seen as an integral part of a comprehensive building concept within the framework of local urban and regional planning (Fig. 1).

The second optimization step involves the dimensions of the building’s components and the way they function (Fig. 4). The energy consumption of buildings could be substantially reduced if project-specific requirements for interior comfort were applied rather than adhering to generally applicable – and in some cases, exorbitant – standards. Ideally, relevant comfort limits would be individually defined for each building zone. The more generously they are set, the greater the scope for energy-efficient measures. For example, the maximum permissible indoor temperature can be increased if the dress code is relaxed on hot summer afternoons. Conversely, the efficiency of passive air conditioning can be enhanced through nocturnal cooling, provided that lower temperatures are acceptable in the morning. The energy-saving potential also increases if lower (or no) standards for interior comfort are adopted when rooms are not actually in use, thus limiting climate control to the minimum necessary to protect the fabric of the building; this can be done with the aid of presence sensors. As a result, the building’s technical infrastructure for internal climate control, ventilation and lighting infrastructure can be reduced in scale – to the extent that it is necessary at all – and then used only in extreme situations. This is particularly likely to succeed when not just the building’s climate control, ventilation and lighting systems are demand-controlled, but also the protective and technical utility functions that are incorporated into the building envelope.

The third optimization step entails transforming the building envelope into an active solar power receiver area, thus reducing the building’s consumption of primary energy without sacrificing comfort (Fig. 9). Thermo-collectors are integrated into the façade for heating and cooling the interior of the building, sometimes teamed with photovoltaic modules for generating electricity. As recently as the 1990s, the design of collector surfaces of active systems for producing solar energy essentially adhered to the production processes of the given manufacturer, with the proviso of producing the simplest standard components possible. In the meantime, these components have evolved into design features (Fig. 10), which can be largely adapted to individual architectural requirements. The spectrum of possible applications extends from façade elements and rooftop modules to sunshade equipment. Meanwhile, coherent, detailed solutions are available for the connection techniques.

The best outcomes are achieved by combining all three optimization steps. These are concepts which, along with climate- and user-oriented buildings and building envelops (that do not just save energy but actually produce it), also contain the relevant building and control technology, governed by optimum building- and user-specific control strategies.

4. Approaches for improving process efficiency

In recent years, construction has grown much more complex. A fundamental reason for this is the desire of principals for “unique” rather than standard solutions. When it comes to greater customer orientation, the key to success does not lie in minimizing external variety through standardization, but rather in the intelligent management of diversity. The actual challenge lies in decoupling the façade costs from the functional and design quality of the façade. Thus, what is needed is a highly efficient planning and construction process which takes full account of energy and material efficiency as well as the design quality of the building envelope (Fig. 7), accompanied by a systematic management of variants.

4.1 Structuring the construction process

The division of labor is crucial to achieving greater process efficiency. It entails dividing different processes into various sub-processes, which are then carried out by various specialized individuals, departments and companies in an organized form of cooperation. It was thus that the division of labor arose during the structuring of the building process, giving rise to the various trades that make up the modern construction industry, including those specializing in façades: the developers, planners, producers, subcontractors and processors. Often, this also entails streamlining the construction process through the industrial manufacture of individual subassemblies, which are then put together at the building site. The skeleton building method proved helpful, as did structuring the building (Fig. 11) into primary, secondary and tertiary structures (interior finishing and technical infrastructure). From the standpoint of rationalization, it is highly advantageous when the three structures are subject to a uniform system of dimensions and modules. It is also helpful when the performance limits for the relevant interfaces, the exchange of media and data, and the construction and geometry of the interfaces are unambiguously defined and then optimized.

4.2 Streamlining the construction process

Deconcentration of work processes and the division of labor between variously equipped companies are underway in the modern process window and façade construction as well (Fig. 12).

Apart from profiles and panels, the term “individual components” refers (in the form of semi-finished products made of metal, plastic or glass) to all other connecting elements necessary for manufacturing windows and facades (e.g. screws and corner connectors) as well as the usual function accessories (e.g. fittings and drives). Modules are prefabricated, preassembled, project-specific subassemblies, made to measure and supplied by specialized subcontractors. Such subassemblies include insulated windows, panels and natural stone as well as sun protection, anti-glare elements, façade ventilators, solar collectors, and PV modules. Finally, these individual components and modules are assembled to form ready-to-function window or façade elements.

Work steps a) through e) are normally conducted in project-neutral fashion, today generally by large, independently operating plants. This involves standardized serial production with the help of highly specialized plant, equipment or machines designed to perform a single function. For example, during the manufacture of individual components, production processes are used in accordance with the “original form procedure” (e.g. casting techniques for connector elements) or metal forming procedure (e.g. casting techniques for aluminum profiles or rolling techniques for sheet metal). On account of the high plant and equipment density, the accompanying high fixed cost ratio as well as the comparative lack of flexibility, this type of production is only used in the first work steps that are serial in nature. Conversely, work steps f) through i) – at least with non-standardized assemblies – are conducted on a project-related basis. Individual fabrication of components in smaller batches demands considerably greater flexibility. This is achieved by deploying modern workstations and machines that can be adapted to changing requirements, as well as qualified personnel. Thus, semi-finished products today are frequently processed using multifunctional, partially automated machines, an activity which takes place increasingly often in computer-controlled processing facilities. The transport of individual components, modules and subassemblies inside the plant and at the building site also offer scope for rationalization, and the same applies to the various work steps at the site. For example, various hoisting devices are used at construction sites. Depending on the requirements, stationary or mobile winches, elevators and cranes are employed in order to deliver components to the required location. The size and weight of the components as well as the dimensions of the building (height of stroke and projection) are factors that determine the type of hoisting devices used, together with the required positioning accuracy.

4.3. Improving efficiency and quality through standardization and unitization

Standardized, project-neutral components and the principle of pre-assembly make it possible to reduce the volume of project-specific activities (steps f, g and h in Fig. 12). In addition, from the standpoint of sustainability, transferring work steps from the building site (step i in Fig. 12) to the factory (steps f and h) is a useful means of managing complexity, particularly during building and disassembly (Fig. 13).

Thus, material- and fabrication-related tolerances and movements are shifted constructionally to the outer edge of the modules and/or subassemblies. They thus lie at defined, predictable interfaces. The subassemblies should thus by usable in the building as a unit, and feature fittings that facilitate their connection to the unfinished shell of the building and in internal finishing work. Detachable, easily accessible connectors and mounting materials (façade mountings) compensate for the building shell tolerances. Compared to construction methods with a lower degree of preassembly, independence from the effects of the weather reduces the need for unplanned improvisation and lays the groundwork for steady, dependable quality. Standardization and panelization both contribute to greater predictability and enhanced potential for optimized work sequences. They form a sound basis for the mechanization of work steps, thus making the process of façade construction more efficient.

4.4 The System Construction Kit

The greater the degree of standardization, the less complex the process becomes. When it comes to office and administrative buildings or high-quality residential architecture, however, this has nothing to do with standardizing the entire building’s form or division of space, nor does it have any bearing on the dimensions or colors of the windows and doors. Rather, it refers to the form and characteristics of the individual parts and modules from which ready-to-function individual assemblies are put together on a project-specific basis. Here, the interfaces between the individual components and modules play a crucial role (relevant in the factory) and between the assemblies formed from them (relevant at the building site). This leads to a scalable system of building blocks (Fig. 14).

This consists of a large, well-organized collection of standardized, serially produced, and sometimes preassembled, components (e.g. insulated profiles) featuring defined characteristics, dimensions and tolerances. From these individual components, defined combinations (relationships) can be put together using system-intrinsic connection techniques (an essential difference from standardized semi-finished products such as FLUTZ profiles), thus creating project-specific, made-to-measure windows and façades. There are various series within the building block system. The analogous components of related series adhere to the same constructional and fabrication principles and consist of the same materials. In principle, they fulfill the same function, and cover a broad field of applications thanks to various geometrical, mechanical (e.g. static) and physical (e.g. thermal) dimension levels.

The joints between the individual components and modules play a decisive role not only with regard to the functional and design characteristics and quality of the windows and façades, but also due the potential for automating certain work steps. In this context, extruded aluminum profiles are a valuable semi-finished product. Their multifaceted, individually designable forms and cross-sections give design engineers abundant scope for creativity. With regard to their cross-sections, extruded profiles can be designed to minimize the need for subsequent mechanical processing. Owing to the comparatively low tool costs for aluminum extrusion, even the manufacture of individually designed special profiles is economically feasible. However, it is also important to take into account the expenditure necessary to ensure that the special profiles not only meet the required functional specifications, but also the qualitative requirements. The fabrication and assembly aspects are especially important here. Moreover, aluminum is a good lightweight construction material, with the added virtue of being an excellent recycling material: its specific material characteristics remain unaffected when the product is used; nor are the harmed by the recycling process. The recycling process requires up to 95 percent less energy than primary aluminum production. Recycling-minded design of the façade components is, however, an essential prerequisite. Designs that enable simple dismantling of the components and easy separation of different materials are of course advantageous. The surface of aluminum can be improved through various processes to meet a wide spectrum of functional and design specifications (step d in Fig. 12). With the aid of the electrolytic oxidation process (“ELOXAL”) and various mechanical and chemical pre-treatments, the surface quality, the resistance to corrosion and the decorative appearance of aluminum materials and components can be influenced in a specific manner. Organic coatings on aluminum surfaces (powder coating or wet paint finish) provide protection from corrosion as well as offering a wide variety of colors for design purposes. In order to maintain the desired characteristics in aluminum surfaces in the long term, however, regular cleaning with suitable cleansers is necessary.

5. The conception and planning of sustainable building envelopes

Principals and building users will only really be happy with their building when, on the one hand, the property-specific specifications and parameters are clearly resolved, and, on the other, the ensuing objectives of the planning specialists and the executing companies are systematically implemented. For this to happen, the planners need to be familiar with the relevant technical possibilities, whose applicability must be thoroughly evaluated. Hence, it is imperative that a concrete definition of the project be formulated prior to conception and planning of the building envelope. The initial objective here is an early, solution-oriented definition of the entire building project, i.e. the “catalogue of specifications”, including the principal’s budget for investment, operating and maintenance costs.

In the conception phase, an interdisciplinary planning team prepares several basic approaches to a solution, with which the project-specific parameters and requirements defined in the catalogue of specifications can be achieved by exploiting the latest engineering and functional possibilities as well as taking design aspects into account – ultimately delivering the best-possible result. Here, energy efficiency plays a central role (cf. Chapter 3). Diverse priorities come to the fore during this phase, depending as to which aspect of the building is to be optimized – economic, ecological or socio-cultural – and to what extent. In this context, it should go without saying that the latest possibilities can only be fully exploited when the various building trades are fully taken into account.

At least in the case of complex building projects, actual planning of the façade should be divided into variant and integration planning as well as subassembly and detail planning. In façade construction, the term “project structuring” refers to the division into assembly segments as well as different façade types. In the process of project-specific categorization, first those façade areas with similar design and functional requirements are identified. Representative basic façade types are defined for each area. A careful survey should be conducted to determine whether a few types (with many relatively diverse variants) or many types (with many relatively similar variants) should be defined. It can prove advantageous during this early phase to determine if various functional and design specifications can be met through additional elements (e.g. outside or inside sun protection and/or filling elements made of various materials or with varying surfaces), and thus be defined as similar variants (“basis variants”) of the basic façade types.

These basic façade types are to be optimized with respect to specific requirements and their fundamental sustainability aspects. First, during the variant and integration planning phase, project-specific solutions relating to the sustainability aspects of the building’s lifecycle are studied and evaluated in detail for each type of façade, building on initial proposals generated in the concept phase. The selected concept is then worked through, and an integrated solution drawn up with the participation of specialist engineers and government authorities as well as consultancy companies and product manufacturers. In order to obtain optimum results, complete systems whose individual parts interact with each other must be examined. It is only when the results of integration planning conform to the project objectives that subassembly planning can start. Here, the aforementioned basis façade types must be optimized with regard to the specific requirements and basic aspects of sustainability. Apart from energy efficiency (cf. Chapter 3), the focus is on technical matters relating to fabrication, assembly, and disassembly as well as the creative integration of load bearing, security, safety and utility functions in conformity to the specifications. By decoupling the functions and the specialization of individual components, advantages arise not only for the planners and metalworkers, but also for the subsequent user. If rational and warranted, supporting simulation calculations and testing of sample facades can be conducted at this time; Schüco also furnishes the necessary test certificates.

Material-efficient buildings minimize the consumption of material during construction (this is known as “material intensity”). Moreover, their components are optimized for maximum durability as well as enhanced recyclability. A particularly effective means of enhancing material efficiency – and which has yet to be fully exploited – is lightweight construction, which typically falls into three categories: material, structural and system lightweight construction (Fig. 15). 

Material lightweight construction refers to the optimized selection of materials for special applications that feature a favorable ratio of specific weight to usable stability, flexibility or rigidity. Aluminum has proven advantageous in this respect. Structural lightweight construction relates to the type, number, arrangement and fitting of components from which a supporting structure is built. In this context, it is perfectly permissible for an individual component to be heavier if it means that the entire bearing structure becomes lighter as a result of the interaction of individual components. This requires a detailed analysis of loads and forces. Rough estimates – underpinned by generously calculated margins of error – result in wasted materials due to over-sizing. The third category is system lightweight construction. This refers to the principle by which a building component not only serves as a load-bearing element, but also performs other functions. It is the normal way of building façades today, entailing the optimum design and selection of materials, which in turn presupposes comprehensive knowledge of the material-related influencing variables that affect the various functions.

Once a project is awarded, the architects, specialist engineers, entrepreneurs and product makers jointly engage in detailed planning for its execution. The process begins with the creation of a schedule for engineering, fabricating and installing the façade. Here, the work at the building site is assumed – the actual work of installing the façade – since it is there that the physical contact with other trades takes place. Consequently, scheduling of installation of the façade must be coordinated with plans for completion of the building shell and finishing work, in line with defined assembly segments. Proceeding from this, scheduling of fabrication lots for various types of façade takes place in reverse order, sometimes with overlapping installation segments in the case of small lots. The schedule for developing and procuring the façade types and their individual components derives from this, once again in reverse order. At least in large-scale façade projects, it is during this planning phase which, at the very latest, the guidelines discussed in Chapter 4 for improving process efficiency should be taken into account. During engineering, combinations of individual components from the System Construction Kit should be applied as far as possible. Finally, following completion of a basic façade type, processing of the similar basis variants takes place; then the order and fabrication documentation is prepared for all of the individual variants deriving from this, a process involving parameterized construction of variants (“configuring instead of constructing”). 

Schüco’s custom-designed calculation and construction software (SchüCAL / SchüCAD) with built-in construction component library is helpful here. The system-typical reutilization of documents for technical drawings and the work planning process also offers advantages. Thus the groundwork is finally in place for the economically viable production of variants. As the project progresses, specification-driven logistics, particularly the procurement and delivery of project-specific, industrially manufactured, quality-assured building components follows, including the surface finishing required for their intended use. For semi-finished goods and their preparation, the two-fold criteria for success must be dimensional accuracy and consistency of form within the permissible tolerances. As a system supplier, Schüco also develops the tools for processing the made-to-measure tools, devices and machines from the System Construction Kit. In addition, Schüco provides accompanying services such as furnishing the necessary processing instructions as well as providing guidance on processing the components supplied.