Ever since human beings began to handle metals around 6,000 B.C., the development of metallurgy has been associated with humanity’s revolutions – not only the technological, but also the economic, social, and cultural ones. But the incorporation of metals into architecture as an intrinsic element of it, not only as materials with auxiliary or decorative uses, did not happen until well after the first Industrial Revolution, during the period of architecture of iron, mainly the 19th century. Cast iron first, then steel, progressively took up an important niche among structural materials, practically claiming hegemony until the popularization of reinforced concrete during the early decades of the 20th century.
In architectural roofs, using lead became notably widespread in the same period (though had started long before) thanks to its malleability, resistance to corrosión, and excellent impermeability properties. At the end of the 1930s, the advent of the curtain wall brought on the appearance and development of the industrial use of metals as materials for architectural enclosures, a process which has accelerated in the last decades in line with a new technological revolution.
The metals that have been finding their way into the production of architectural enclosures are quite varied, with each one of them contributing its own unique characteristics. They have a bearing on the final appearance of buildings, thanks to their particular aesthetic features, which differ substantially. Much in use, for example, are carbon steel, aluminum, and stainless steel (see Arquitectura Viva 166 and 173), numerous applications of which exist in the market. Less widespread but also with a notable presence from a qualitative point of view are metals like tin, lead, titanium, copper, and zinc (see Arquitectura Viva 170 and 180), not to mention an infinite number of alloys and compounds that have been flooding the industrial catalog of solutions for architectural skins. All of them are used for the basic purpose of serving as solar filter and protection against wind.
Metals are also commonly used to separate the thermal envelope and generate passive ventilation in air chambers, given that the high conductivity and low thermal inertia of metals make it inadvisable to use them alone as enclosures. Guillermo Hevia takes advantage of this effect in the Nestlé Social Block, in Graneros (Chile), by putting perforated plates of CorTen steel on the outer skin. In this way, the humid air resulting from the evaporation of the circular perimetral pool is forced to move within the double skin, thereby naturally cooling the building. Also frequent is the use of metallic enclosures as protectors of privacy and as screens against unwanted onlookers, whether by perforating the material or through louvers, which come in a very wide range of geometrical patterns (see Arquitectura Viva 161).
Metal skins are mainly characterized by their lightness. Unlike non-metallic materials, they are able to serve as protective barriers even as very thin (albeit highly dense) plates. Durability is another fundamental characteristic of these materials. They are highly stable over time. Oxidation is of course a problem, but there is a large variety of strategies for keeping the negative effects of rusting stabilized or under control. Another strong point of metals is that they can be recycled and reused in their entirety, and the energy footprint of recycling metals is considerably less than that of the recycling of other materials.
Practically all metals are available in the market under the same comercial product lines, and use of them in designing enclosures varies greatly. As material for finishes, metals are ideal in refurbishments of existing buildings, as in the Edogawa Garage Club renovation by Jun’ichi Ito Architect & Associates.
Through casting, metals can come in a diversity of shapes and sizes. With fine wires braided to form ropes and cables we can even come up with metallic fabrics similar to textiles, fabrics in combinations that yield a huge selection of patterns and textures, such as those used by JFAK Architects in the Los Angeles Police Department. Flexibility in both the design and the finish allows much freer adaptations than is possible with other enclosure systems.
Meshes and Louvers
Electro welded wire mesh, unlike cloths, have a more fixed geometric pattern. The combination of wires and plates of varied thickness also allows an infinity of textures, from very dense lattices to near-transparent sheets. Cristina Díaz Moreno and Efrén García Grinda (amid.cero9) use bars of galvanized steel to clad the buildings of the Giner de los Ríos Foundation, which are distributed around the garden, the densities of the meshes depending on the desired degree of visibility and permeablity to light.
The manufacture of preshaped louvers with a great variety of forms and designs also makes for a very wide range of solutions, since these can also come in many materials: aluminum, stainless steel, copper, and prelacquered steel with an endless selection of colors. Aluminum wire meshes and panels of stainless steel were used by Foster + Partners in the Banque Marocaine du Commerce Exterieur (BMCE) branches, where the facade presents an external lattice arising from a geometric pattern.
Laminating metal allows preparation in plates of very varied thickness. These plates can be continuous surfaces, or they can be perforated. Thanks to advances in production with computer numerical control (CNC), the latter have revolutionized the system, allowing total design freedom with much reduced production costs. The facade of the Surry Hills Library and Community Centre in Waur, Australia, by Whitefeld McQueen Irwin Alsop Architects, is covered with perforated plates in diverse patterns, resulting in a highly dynamic facade. A variation in the perforation is the mechanical banging of flat plates and meshes to create a three-dimensional texture, as Herzog & de Meuron did in the CaixaForum of Madrid.
These sheets and plates can be bent and made to form waves, giving rise to another family of elements that is widespread in architecture: preshaped plates. Driven by the designs of Jean Prouvé from the mid-20th century on, use of these spread to all kinds of constructions, in facades and in roofs. A good example is the cover of El Molinete Archaeological Park in Cartagena, by Ammann, Cánocas, and Maruri, where the ribs are placed on different planes, in alternation, resulting in a faceted complex which is highly sculptural.
Trays and ‘Cassettes’
The system of trays with lock-seamed joints is the most common way of commercializing the more malleable metals, such as zinc, copper, and lead. More habitual in roofs than in facades, the system has just one drawback: the thermal dilation of the material, which, being greater than in others, and having to adjust to smaller thicknesses, potentially causes major deformations.
With volumetric bent metal sheets, generally of steel or aluminum, the so-called ‘cassettes’ are formed which make it possible to clad blind surfaces, leaving the joints exposed and put back and giving the continuous facades the desired rhythm and volume.
Among composite systems, multilayered panels have had a successful entrance in the market, and they are widely used in both roofs and facades. With an insulating core, generally a rigid foam of polyurethane (PUR) or polyisocyanurate (PIR), the panels consist of two metallic sheets with Kraft paper on the outside, which are usually of embossed or lacquered aluminum, prelacquered steel, or galvanized steel: a multilayered composition that counters one of the major disadvantages of metals: high thermal transmittance.
In the final analysis, the geometric possibilities – for uses, finishes, and textures – that metallic skins offer are practically infinite. The existing technology for producing materials and the knowledge we have of how materials behave currently provide us with innumerable solutions where the only conditioning factor is the designer’s imagination.