Building envelope: concept, classification and types

The building envelope is an architectural element that defines and concludes the perimeter of the body construction and structural (it is therefore called "frontier"). Its function is to mediate, separate and connect the inside with the outside, but it is also an environmental element, which defines and identifies the external spaces surrounding.

The building envelope consists of all drives technological and technical elements that define morphologically and functionally in three directions, interacting system, the boundary between the internal environment (set of spatial elements and environmental units which must ensure that the needs of 'user) and the external environment (environmental context, boundary conditions) of a building structure. We define building envelope dry construction type of housing in which all the units of technological and technical elements (components and systems elements), with load-bearing or non-load bearing joints are assembled with dry and fixed to a structure through the main anchor systems (bolts, screws or welding). 

1. The concept of wrapping in building

The use of the term refers to the building envelope is fairly recent, and an evolution of the concept of closure, which identified as separate units together, the external walls (horizontal, vertical, opaque, transparent, etc..). In contemporary building the building envelope, which identifies the entire locking system outside, is divided into several functional layers and materials and is increasingly being investigated in its relations with the structural system and the plant.

2. Evolution of the building envelope

The primitive man's need to build their own habitat artificially changing the natural resources available, has led to the creation of shelters safer and more sophisticated and this initial need was expanded and transformed into a system of needs in growth and in the search for a balanced relationship between the natural world and man-made. In the past, constructive practice was dominated by the Rules of Art, remain identical and transmitted from generation to generation, so as to preserve the balance of nature, able to absorb the changes produced by man, plus it was a widespread practice that the recycling of materials and the re-functioning of the buildings, motivated by economic reasons and time, which contributed to the minimal use of new materials.

The evolution that the building envelope has undergone over the decades, has generated growth requirements, motivated by a significant increase in performance, complexity and the range of products offered to the designer and from refining the techniques and materials traditional.

The seventies were marked by a particular interest in issues related to thermal insulation, creating a rapid development, across Europe, opaque envelope insulation techniques such as double glazing and frame with thermal tightness.

The introduction of artificial materials and industrial and processes of social and cultural evolution have led to the transformation of masonry load-bearing component of the building to the perimeter of the building, giving rise to the gradual breakdown of the functions in the carrier, protective film, thermal and acoustic insulation etc..

The building envelope in the process of research and experimentation, technological and architectural element has evolved from a complex system-protective barrier filter to optimize the interactions between external and internal microenvironment.

The building envelope has become increasingly an area of border dynamics, able to vary their performance to changing external environmental conditions and the needs of those who live in the interior and can accommodate plant devices of various kinds.

This attitude has generated a radical change from culture dissipative it has gone to conceive Housing as a device capable of exploiting natural resources to produce energy.

3. The passive envelope

4. The casing active

The building envelope enclosure becomes active when not only supports, but incorporates in its structure plant systems, those for the collection and conversion of solar energy and artificial ventilation of the interior, it is more energy efficient and more controllable in functional terms with respect to the passive. Despite this greatly limits the architectural expression because of the modularity dimensional typical of plant components and creates problems for the design of the facade according to the layout of the rooms.

The solutions adopted more frequently and have found that the most successful are using the glass wall and ventilated facade integrated with a photovoltaic system. The first is formed by two transparent surfaces separated by a gap and artificially ventilated through air vents and the second is composed of a series of solar cells integrated into the glass walls. Photovoltaic cells with their location and their textures enhance the communicative potential of the building envelope and formal.

5. Housing hybrid

Experiences of assets and liabilities on the wrappers and reflections on projects such experiences have anticipated or later lead the architects to design the enclosures as hybrids. The casing is set hybrid passive and active, because it is capable of performing various functions, and dynamic, because it can modify its performance physical techniques in time, in relation to climatic conditions and the needs of users. Despite this, many doubts arise both on its sustainability than the other two types, that compared to the complexity, adopting systems functionally and technologically very complex. Moreover, construction costs are far higher than those of conventional casings, not to mention the high cost of maintenance caused by the complexity of the components and their mutual positioning.

6. Energy efficiency of the building envelope

The growing interest in environmental issues has meant that the building envelope is no longer be considered only as the separator between inside and outside, but as a dynamic interface in continuous and active interaction with the external climatic factors, for example during design, construction and operation of a green building. The efficiency of the envelope is given by the ability to react flexibly to changes in environmental conditions, minimizing the heat losses in the winter period and limiting the rise in temperature in the summer, with the consequent improvement of the living comfort and environmental quality , obtained without the use of nonrenewable energy sources.

"If you mean the casing as a" skin "that protects the interior from the elements but at the same time it leverages the power in a functional way, then we can think about the creation of a protected controllable. In this case the external environmental conditions become an asset and not a force to contend with, while the case a "reactive skin" that improves the well-being inside and evokes many possibilities for change. [1] »


7. Break it down into elements and layers

The locking system of the building envelope Cleaning consists of the following elements and layers:

• The carrier, the structure to which are attached with different coupling systems the other strata of the casing, can be simultaneously a structural element and tamponade.

• The anchoring element, is a system or component of the façade system whose purpose is to carry or hold the cladding elements.

In the design of coating systems, the anchor is the fundamental element of the interface between the coating and the support structure. It consists of elements assembled with dry technologies; elements must be chosen and calculated in function of the type of surface, of accidental loads and permanent in operation, the type of coating and the distance between this and the support structure. The anchoring system dry, also provides support devices and retention in the desired position, the adjustment in the three spatial directions, the transfer of the horizontal and vertical loads, and absorption of the settling and differential expansion in respect of the lining elements.

• The layer of infill and outer coating, which can be realized in different ways: continuous coating systems, systems assembled elements, etc..

An increasingly widespread evolution of components allows for elements characterized by multiple combinations, with which it is possible to exploit the potential synergies between different materials and allow integration of multiple systems and residential construction.

8. Classification according to building system

From the point of view of the construction system, the types of casing Cleaning are distinguished:

• Structures composed of mullions and transoms;

According to UNI prEN 13119 type mullion and transom is defined as a supporting lightweight components assembled on site to support panels opaque and / or translucent prefabricated. The structural grid of the facade is made up of the implementation of vertical and horizontal bars connected to them. Subsequently, the frame constitutes the support of the infill elements, doors and windows that open. In some solutions as a last step, the panels are fixed to the frame external protection (screens or coatings).

• Structure in cells or units;

In accordance with the UNI prEN 13119 structures in cells or units are represented by "pre-assembled modules, interconnected, height corresponding to one or more floors, complete with panels." The main advantage of this system is that is constant and guaranteed the quality of individual pre-assembled elements, because they are made in the workshop through industrialized processes which provide high controls.

• Structures composed of mullions, transoms and external displays

This system, which represents the evolution of the system of assembly described in the first type, is constituted by a main structure of mullion and transom and an additional structure projecting outwards (often in turn formed by brackets and fastening rods) that supports a screen with various functions, mainly protection from rain or insolation.

9. Types and envelope solutions dry

The evolution of systems of building envelope dry is characterized in terms of technology-performance by increased complexity and rising levels of quality of services provided, and in terms of architecture from the research of languages and different architectural styles, often linked to materials used for the coating layers (glass, stone, brick, metal, wood), for example in the design, implementation and management of a green building. In their evolution the different types of solutions have been referred to, in literature and in practice, in several ways. Below are some of the names, pointing out that this is not a classification and that the same technical solution can be called in several ways depending on the aspect that characterizes you want to emphasize:

• The layered system dry Structure / Coating.

It is the product of an appropriate stratification of construction elements thin, light and high performance. In layered structures, each assembly of different technological layers corresponds to a different set of physical performance, which can be defined in the design phase, through an analysis of performance. The construction of packages Cleaning also allows a greater attention to detail, the possibility to choose the most appropriate materials to be assembled, the possibility of continuous variation, an optimization of the stratification of the casing and greater maintainability of technological units.

• The curtain wall or curtain wall

In accordance with EN 13119, a curtain is "an external façade of a building made from scaffold made mostly of metal, wood or PVC, usually made up of vertical and horizontal structural elements are connected together and anchored to the structure of the building" . This ensures, by itself or in conjunction with the remaining parts of the building, all the normal functions of an outside wall without having to contribute to the functions of the bearing structure. The curtain or curtain wall is characterized in terms of performance and aesthetic by a continuity of the casing with respect to the bearing structure of the building, which remains fully retracted relative to the plane of the facade.

• The ventilated facade

The UNI 11018, defines the ventilated facade as "a type of facade in advanced screen in which the interspace between the coating and the wall is designed in such a way that the air present in it can flow to the chimney effect in a natural way and / or in artificially controlled way, depending on the need seasonal and / or daily, in order to improve the overall performance termoenergetiche ". In this case the solution "dry" may only cover the screen "advanced" or coating in front of the ventilated cavity.

• Structures in rainscreen (Rain Screen Cladding);

In this system, characterized by an assembly system with mullions and transoms, the screen acts as protection from rain, from the infiltration of moisture, the space behind the screen is ventilated and does not necessarily contribute to the performance termoenergetiche housing. Even in this case the "dry solution" can only cover the screen.

• The double skin façade

It is a type of facade belonging to the closure system in dynamic insulation. The double skin facades form a transparent continuous along the entire perimeter of the building: the outer skin is fixed - can not be opened - and is designed to protect the building with its own characteristics of air tightness, water and wind, while the second, located inland, it is almost always equipped with doors and windows, and allows you to ventilate the interior spaces without the necessity of a particular control of environmental stress. To improve the comfort inside the building, sometimes, there is provided a natural or forced ventilation of the interspace defined by the two skins. Cavity, in addition, can be inserted continuous dimming devices or blades adjustable from inside the premises and opening elements to air environments.

• The casing for the integrated production of energy

This type of housing allows the integration of photovoltaic panels that convert sunlight into electricity. These modules, for example, can be integrated in closure systems transparent that occur in single-layer or double skin, vertical or horizontal, with angles from 0 ° to 90 ° (with an optimization of the solar collection through an angle of 45 º with respect to the vertical). The system also allows the integration of solar screens, such as solar shading fixed, mobile and adjustable.

• The housing Interactive

It is called "interactive shell" the system that interacts with changes in external climatic conditions using automatic control devices or through the direct intervention of users; casing that allows the control of the level of performance offered by the closure by changing the values of the parameters and hygrothermal environmental related to the internal microclimate.

• The housing Interactive Multimedia

Interactive multimedia is defined casing a system designed to rear of still images or moving on the inner surface of the transparent panels. In this case, the skin of the building is constituted by vertical paneling - always mounted on metal frames support - formed with translucent materials coupled together whose properties allow the projections to appear outside with decorative effects also very spectacular (often, in fact, the system is used for advertising purposes).

9. 1. Significant examples of facades dry described

Layered system dry Structure / Coating:

• Housing and Neighborhood Library in Evreux, France (project Dubosc & Landowski).

• Restructuring of the hospital expansion Ceccarino, Riccione (RM), (project Ettore Zambelli)

• Research Centre Campus Point in Lecco (Studio project Ardea)

Curtain wall system:

• Seagram Building in New York, USA, (project Mies van der Rohe)

• Earthquarters Willis Faber and Dumas in Ipswich, England, (project architect Norman Foster)

Ventilated facade:

• The Cité International in Lyon, France, (project architect Renzo Piano).

• Museum of Modern Art in Vienna (project Ortner & Ortner Baukunst)

Structures in rainscreen system:

• Alcoa Building in Pittsburgh, USA, (project H. Wallace Harrison and Max Abramovitz)

• Federal Building in San Francisco, (project Morphosis Architects)

Double skin facade:

• The building Helicon in London, England, (Sheppard Robson Project)

• Manulife Financial in Boston, USA, (Skidmore project Ownigs & Merill Architects)

Integrated casing for the production of energy:

• Solarfabrik in Freiburg, Germany (project & Rolf Hotz)

• Library of Mataró, Spain (project Miquel Brullet)

Housing interactive:

• Institut du Monde Arabe in Paris, France, (project architect Jean Nouvel)

• The office building in Wiesbaden, Germany (project Thomas Herzog & Partners)

Housing interactive multimedia:

• Ferry Terminal White Hall in New York, USA (Scott Brown & Associates)

• The building La Fayette in Berlin (Jean Nouvel)

10. Technical regulations

• UNI En13830 Curtain - Product standard

• UNI prEN 13119 Curtain - Terminology

• UNI En 11173 Windows, doors and curtain walls - Selection criteria based on air permeability, water tightness, wind resistance, thermal transmittance and sound isolation.

• UNI En 11018 Coatings and anchoring systems for ventilated facades in mechanical assembly operating instructions for the design, execution and maintenance - stone and ceramic coatings

• UNI EN 12152 Curtain - Air permeability - Performance requirements and EWC

• UNI En 12153 Curtain - Air permeability - Test method

• UNI En 12154 Curtain Walls - Water resistance - Performance requirements and classification.

• UNI En 13116 Curtain - Resistance to wind load - Performance requirements.

11. Notes

1. Thomas Herzog (2005).

12. Bibliography

• Thomas Herzog, Roland Krippner, Werner Lang, Atlas of facades, UTET, Turin, 2005;

• Christian Schittich (ed.), Building Envelopes, Birkhäuser, Basel, 2001.

• S. Altomonte, The architectural shell as a dynamic interface - tools and criteria for sustainable architecture, Alinea, Florence, 2005;

• G. Boaga (ed.), The architectural shell, Masson, editorial ESA, Milan, 1994;

• Blackboard Monica, Sustainability and energy saving. Technical solutions for eco-efficient wrappers, Clup, Milan, 2006;

• Gianmichele Panarelli, Philip Angelucci, Enclosures energy, Hall publishers, Pescara, 2003;

• Mark Hall (and others), solar screens, Alinea Editrice, Florence, 2005;

• Fabrizio Tucci, The Well-Tempered Housing - Energy efficiency and ecological architecture through the skin of the buildings, Alinea Editrice, Florence, 2006;

• Aurelio Fusi, Advantages of thermal inertia in the building - project 1978-1979, Journal technique of Italian Switzerland, "Towards a house without heat loss - experience in Breganzona (CH)", no. 2 (February 1982)

• Altamonte Sergio nvolucro The Architectural Interface How Dynamic Publishing INTRODUCTION

• Alan J Brookes, Chris Grech, The Building envolpe. Butterworth & Co., 1990

• Cup Alessandra, Barbara Borello, Facades Dry Fererico Motta Editore, Milan 2006

• T. Herzog Kripper R, Lang W, Atlas of Facades, UTET, Torino 2005

• Emperor Marcus Procedures Structure / Coating For Construction Sustainable Maggs Publisher, 1999

• Laura Pedrotti, Technological flexibility of facade systems. Evolution of the techniques of production and assembly, Angeli, Milano, 1995.

• Oesterle, Lieb, Lutz, Heusler Double-Skin Facades Prestel Verlag

• Ettore Zambelli-P. A. Vanoncini - M. Imperadori, Construction dry stratified Maggs Publisher, 1998.

• Structures UNIedil 2006 Technical standards for the facilities, the casing and finish of construction, update October 2006.

12. 1. Magazines

• Build Dry - non-traditional systems, Year II, n º 14, June 2007

• Build - Special Wrapping, "The all-glass curtain wall", n º 286, March 2007

• Module - "The Construction Layered Dry", No. 273 July / August 2001




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