Glass as a Building Material

Michael Elstner, Head of Interpane Beratungscenter (IBC), Plattling, Germany

Glass as a Building Material
Glass is the dominating material in modern day architecture which places optical emphases and provides for numerous technical functions. Today, the glass industry offers glazing with individual technical features that can be used for heat, solar, or sound protection, as design components, safety glass, or as a part of solar systems. The main focus in building is usually on saving energy, especially in these challenging times of increasing prices for energy and raw materials. The strong differentiation between the technical functions in turn makes individual consultation even more important.

Glass is no longer just a filler element, but is rather nowadays also used for supporting or enveloping purposes. A closer examination of this multifunctional building material requires a look at its historical background and also at the fast developments of modern times.

An insight into the history of glass

Glass as a Building Material
Flat glass has been used as an enclosing element for approximately 2,000 years and is thus one the oldest man–made building materials. Due to constant developments in manufacturing and refining methods, it is now also one of the most modern building materials with an unparalleled influence on the appearance of our architecture. Now that this material can fulfil nearly any task in a modern building envelope, it has been made possible to overcome the antagonism between the human basic need for protection from the outside world and the demand for natural daylight.

Before industrialisation, flat glass was produced, e.g., by means of manual methods such as casting or cylinder technology. These were replaced by sheet glass and plate glass manufacturing methods, which were used up until the 1960s. Machine methods had the disadvantage of distortion and waviness. The manufacturing of the higher quality plate glass was more expensive due to the necessary grinding and polishing. Although enormous improvements have been made for both methods over time, the disadvantages could not be totally eliminated. It became necessary to strike new paths in order to cover the increasing demand for high-quality flat glass. In the early 1950s, the English company Pilkington Brothers developed an industrial solution for producing high quantities of large glass panes of a consistent high quality and at a relatively moderate cost, which was an almost entirely automated float glass manufacturing process. It was in this way that glass became a mass product and was thereby affordable for everybody. In the 1970s, new energetic requirements arose, which were easily fulfilled by modern glass. Until then, single glazing was the standard but had the disadvantage of extremely high heat losses (Ug = 5.8 W/m2k). The development of insulated glazing and its quasi legally decreed use as of 1977 led to a drastically improved heat-insulating value of 3.0 W/m2k.

Glass as a Building Material

As a result of the oil crisis in the late 1970s, the glass architecture at that time was subject to increasing criticism. Uncoated flat glass was considered a waste of energy. An ecological and economical milestone for more energy efficiency was the manufacturing of heat and solar protection coatings by using thin film technology.

Interpane was one of the first companies to successfully market neutral heat protection coatings. One example is "iplus neutral" (since 1982): It is considered to be the first color-neutral thermal insulating glass in glass history. The key to success was a special silver coating. This technology is now the basis for the manufacturing of high-quality thermal insulating glass.

Glass as a Building Material

Glass for windows and facades

"At the beginning, the desire is to design, not the respective function. The function "slips in" (Professor Klaus Pracht, architect and author in Bad Muender am Deister.)

Apart from the primary purpose of a window, more and more additional features, mostly application and structural solutions, have been demanded. As a result, we now speak of functional glazing and facades. Primary use (inter alia)
  • Supply of natural daylight
  • Protection from rain, wind, and cold
  • Transparency or translucency
  • Means of communication
  • Supply of fresh air
  • Secondary use (inter alia)
  • Heat protection
  • Sound protection
  • Solar protection
  • Object and personal protection
  • Fire protection
  • Temporary heat and solar protection
  • Use of solar energy
  • Living comfort
  • Means of design
  • Electromagnetic dampening.
These purposes, which are characteristic for windows, can be achieved by means of special multifunctional designs. Sophisticated window and facade systems combine technical demands with the creative freedom of planning. Such systems are a challenge for architects and manufacturers. With the increasing demands of window and facade systems, the demands of glazing also increase in terms of quality and versatility. Most requirements concern increased protection, which can only be achieved with modern functional insulation glazing. Multifunctional insulation glazing incorporates numerous such protective functions. One example is "iplus city E" for upscale residential construction. It incorporates effective heat insulation with an Ug value of 1.1 W/m2k, effective burglary resistance (safety class P4A), and good sound insulation up to 40 db (in window: sound proofing level 3.)

Depending on the design requirements, the potential of glass is not only in increasing the transparency and, therefore, the quality of living, but it can also emphasise the vitality of reflecting surfaces and the presence of structures.

Even during the planning stage of a building, the technical performance of insulation glazing becomes even more important. Whoever contracts out for windows and facades, has to provide the exact physical data as part of the technical specifications. In order to be able to fulfil the versatile demands in accordance with the technical regulations, co-operation among the architects, engineers, planners, and manufacturers involved is a key factor, in which consultation becomes mandatory.


The developments in the glass sector are not at all limited to its classic properties, such as energy savings and solar protection, but can also improve and change its stability and surface. Many times, nature is the role model, e.g., in the case of the lotus effect. Innovative solutions for decorative facade glazing are another favourite with planners. At glasstec 2008 (Messe Düsseldorf, October 21–25) Interpane showed the design glazing "ipachrome", which offers new possibilities for creative object design by means of large-area or partial coating. The multi-layer system makes the glazing just as highly reflecting as a conventional silver mirror.

As product versatility increases, so does the need for architects, planners, and building owners to consult with the glass processor. Interpane Beratungscenter (IBC) in Plattling, Germany, as well as services architects, engineers, planners, processors, and institutional building owners are all reachable inside and outside of Germany by telephone or on-site. Apart from architectural and technical consulting for facade and window construction, they focus on training as well as national and international co-operation between architect consultants and consumers.

John Lewis Department Store, Leicester A glass facade that's like lace

The 5,000 square metres of ipachrome design: chrome–coated layer system generates variable solar protection / a "glass curtain"

The new "john lewis" department store in the british town of leicester is covered with a dazzling, lace-like curtain that at night is backlit in 256 colors. It is actually a double facade of structural glazing with a very elaborate patterning. With the radical yet inspiring proposal to use a transparent, elegantly patterned full glass facade as an outer skin, foreign office architects (foa), london, won the competition for the design of the 25,000 square metre department store. The facade glazing "ipachrome design" by interpane allows for creative yet functional optics: the design, which was applied in a sputter process, also serves as solar and visual protection and allows for variations in the transparency of the facade.

Glass as a Building Material

The english town of leicester is known for its multiculturalism. Every fourth inhabitant has indian roots. More than half of the youngsters there come from india, somalia, jamaica, bangladesh, uganda, or pakistan. In some schools, more than 70 different languages are spoken. And leicester's economy is booming – restaurants, textile factories, fashion stores. Now, the new "john lewis department store" can be found right in the middle of this illustrious society, and with its patterned, net-like facade, it not only gets many admiring looks, it also fits beautifully into this colorful city. At night, the noble facade is illuminated from the inside in 256 different colours.

Structural glazing with design coating

Structural glazing provides for a particularly harmonic facade appearance, because the mountings for the individual glass panes are invisible from the outside. The glass panes for the facade of the "john lewis department store" were lowered from up above and were then horizontally glued. Apart from a very harmonic and homogenous optical appearance, this also brings about practical advantages: rain will rinse any possible dirt off the glass facade. In order to protect the inside from outside views, but also to maintain maximum transparency, a sort of 3d architecture was created. The facade was equipped with double glazing, or two layers of the "net curtain." In addition, the inner and outer patterns were offset against each other. From the outside, it looks as if the patterns lie on top of each other in order to keep viewers from looking inside.

Glass as a Building Material

The pattern itself is a new, partial coating, which also allows for delicate, artistic types of object design: "ipachrome design" was developed and designed by interpane in plattling, germany. More than 5,000 square metres of glazing and 625 panes of 2.4 by 5.4 metres each comprise this integral area. The pattern was designed in such a way to establish flowing transitions in order to produce the appearance of a single unit.

The ipachrome design multiple layer system lets the pattern appear like a highly reflective conventional silver mirror from the outside. Unlike other reflective coatings, this one is highly resistant to high humidity. At the same time, the eye-catching ornaments also serve as solar protection, with a transmittance of only 4 per cent. The glass panes themselves are made of laminated sheet glass (lsg), which is comprised of two layers of 10mm heat-strengthened glass.

MGS Architecture January February 2009