For centuries, generations have used glass for filling in large “light holes” in massive outer walls. This has drastically changed in the last three decades. Today glass itself forms and shapes the space and creates room enclosures, thus creating transparent architecture that allows people to feel close to nature. Experts use the generic term “façade” to describe any external architectural construction that serves as protection against weather and dangers of any kind.
In addition to science, research and technology, art and architecture in particular have given rise to a host of possibilities of façades made from glass. Aesthetics, functionality and construction are the most important aspects of using glass as an architectural element, and all of these factors must be precisely defined at the start of planning. A glass’s finish on a façade always influences its reflective properties, which can range from being produced so that the glass is very reflective, reflects an overall color, or has a weak reflection. The change of the daylight due to weather, the sun’s changing position in the sky, the colour of the sky and the seasonal change of vegetation influence reflection, and interior light conditions also impact the glass’s appearance from the outside. Glass façades are generally composed of transparent and opaque areas that can be produced so that interior spaces are visible, or are “optically neutralized” and rendered “invisible” by using a specific type of glass. Reflections during the day time also influence whether a person on the street can see into the interior.
The collared adjustment between a translucent window and an opaque balustrade is only nearly possible as the colour impression of the translucent pane is always affected by the room behind the pane and its light conditions. In addition to the original function of a façade, to provide protection, further decisive criteria concerning the functionality are in the focus, especially for glass façades. There is not only the possibility of culling energy from the façade, but one must also consider protection from heat during the summer (see chapter 5.5). Concerning the constructive periphery out of concrete, steel or aluminium it must always be assured that in addition to the static loads due to wind, suction and snow also the glass weight can be considered.
Generally, glass façades must be looked at from two perspectives, namely, function and construction.
8.1.1 Façade functions
The façade function describes the mode of operation of the building shell. There are generally three different possibilities:
18.104.22.168 Warm façade
The insulated cladding system describes a single-shell in which thermal insulation is connected to an interior vapour barrier to a balustrade panel (sandwich panel). This single-shell system is located behind an opaque pane of glass that protects it from the weather.
This sandwich panel is installed in the façade construction as a whole below the transparent insulating glass and attached using clamping strips. The sill’s vapour diffusion resistance is achieved by applying a sealer and edge lipping. Thus, the opaque and transparent elements serve not only to enclose the room and protect it against weather, but also to protect the room from excessive heat, noise and, if need be, to keep fire from penetrating into the room. These opaque panels need a four-sided frame in the form of post-and-beam construction.
22.214.171.124 Cold façade
The physical construction and technical functions are performed in the sill area of a two-shell construction. The outer shell is used for weather protection as well as the visual design. It is designed with a ventilated glass window so that trapped heat and moisture can be removed. This pane is usually made of glass and solar control is color coordinated with the transparent window. This pane is generally made out of sun-protection glass and its colour is coordinated with the transparent windows. Installation options range from all-sided, two-sided to supporting systems attached at various points, which allows for a broad spectrum of individual design. Underneath the transparent insulating glass windows, the thermal insulation of the wall area is taken over by isolating opaque wall areas behind these parapet planes.
126.96.36.199 Double skin façade
This kind of façade goes by many names; it is also referred to as “second skin” or “attached façade”. This construction method principally consists of a flash-off façade similar to the cold façade described above, but the interspace between the two shells for the railing is broader and the transparent façade construction parts, i.e. insulation glass windows are integrated. The attached façade can hereby be installed outside in front of an existing façade for visual and acoustic reasons. This design is called an interactive façade. The interspace is generally used to install additional solar protection measurements, such as fins or roller blinds, and the potential hot air and condensate are gradually transported to the environment.
The alternative is an inner skin additional solar protection in the interspace. This construction, however, allows the warmair generated by solar radiation to escapewith purpose; the air is then transmitted via adequate aggregates to the energy management of the building. This method is called active double skin façade and can reduce the operational costs of the building.
In the past, inner skin shells were mostly made out of solar protection single-pane safety glass. The tendency today is to use laminated safety glass consisting of two pre-tempered glasses due to the increased structural stability that is present in case of failure.
The function of a glass façade is strongly affected by the glass that is used. In the past, “simpler” glass was preferred due to production reasons. Today, Guardian offers a broad range of suitable solar protection glass with combination layers.
This range is generally based on extra white float glass in order to give the outer clash pane in a ventilated façade as much neutrality as possible. Thereby these float glasses, with their stepwise coatings, offer such a broad range of options that no exigencies concerning reflection remain open. The stronger these reflections, the less sunscreens between the glass panes are needed and unobstructed views are possible. This pallet is listed in chapter 10.
With this development of high-tech layers on glass and their pre-tempering and laminating possibilities, as well as their bendability, we offer our customers enormous competitive advantages and new impulses for façade construction. A large number of these types of glass can be finished with many design components to individualize them (see > chapter 8.3).
8.1.2 Façade constructions
Joining the glass to the building and the shell has importance in addition to function.
188.8.131.52 Post-and-beam façade
The majority of today’s glass facade still consists of post and beam. Here, the load-bearing posts extend from the foundation to the roof of the building in a fixed, aesthetically pleasing, and statically determined and technically feasible distance. These posts are anchored to the building design and manage all applied loads. The “long fields” that thus react to the top are then intersected by a defined number of horizontal bolts that bear the weight of the glass and convey it into the posts. After installing the glass and precisely placing the glazing blocks, pressure pads are fixed with screws, both on the posts and on the bolts. The pressure pads fasten the glass elements and seal them. In order to derive the built up humidity caused by condensation water in the rebate area, an inner drainage is installed with an opening to the outside. The optical closing is generally made by cover strips which have to be fixed by clips, and which are available in nearly all eloxal colours. These strips influence mostly the outer colour scheme.
A large number of systems are available on the market. They range from extremely small to very large, depending on the desired visual façade’s appearance and function. Generally, the extremely small profiles do not have an obvious window function, and are installed in ventilated or air-conditioned buildings in order not to interrupt the sophisticated grid design. Post and beam constructions are approved systems and mostly applicable without any legal restrictions.
184.108.40.206 Structural glazing façades
Whereas clamping and cover strips project from the glass surface on the post and beam construction façade described above, the benefit of this bonded façade is that it appears absolutely even. In this design, an aluminium adapter frame, into which the glass element is bonded, invisibly bears the glass load. This module is then mounted in front of a post and beam construction into which the loads are conveyed. The complexity of this façade technique, together with the long term experience of leading glue and sealant producers, make it feasible that structural glazing façades can only be executed as integral systems. The manufacturers of such systems have the concession of the building inspection. Otherwise, an acceptance test has to be made in an individual case before installation.
The glass weight, as well as the weight of the outer pane which appears not to be fixed, has to be distributed generally via mechanical fastening angles into the construction. Such façades, even without the mechanical holding of the outer pane, can be installed in countries such as Germany up to a total building height of eight meters.
In this case, most glazing consists of a special stepped insulating glass with UV resistant edge bonding (see chapter 3.4) which can absorb arising loads and convey them. As outer pane, a one pane safety glass with a thickness of at least 6 mm has to be used. Because of this construction, there are all sided free glass edges which stand in a determined distance to the next element and are sealed with special structural glazing silicone. It is very important to ensure the adhesion from silicone with the glass edges and the compatibility of all used materials (see > chapter 9.10).
The final visual appearance is a plain glassy area, in which the “silicone-seams” nearly disappear. Especially for this façade system, Guardian offers a number of different glasses with the appropriate authorizations.
220.127.116.11 Point supported façade s
This façade technique, of recent development, is based on point-fixed bearing connections as single holders. In this system, the active strengths of the glazing are transmitted to a mostly moveable mounted point supporting button that transports the active strengths via a metallic conjunction into the massive substructure.
In the conventional method, anchor bolts are mounted through the glazing, covered with an elastic core to avoid glass/metal contacts and fixed with counter panes. These covering and fixing panes project from the surface. An alternative are conical perforations that obtain the stability with special, conical fittings by the clamping power on the edges of the boreholes. This form allows even façade surfaces without any outstanding elements.
Another development are holding points, which are placed on the level of PVB foils and thus form a VSG, of which the outer pane is plain and the backside pane has outstanding connecting threads for mounting. The dimensions of the glazing for such construction accounts for the allowed deformation of the panes and the flexibility of the fittings. The arising stresses by loads are induced through the holding buttons without any restraint into the load bearing construction. The joints between the individual glassy façade elements are sealed with UV-resistant closing systems. In this fashion attached façades out of monolithic glasses can be built as well as insulating glazing façades. In the latter, the glass rebate is ventilated through appropriate systems and enables the condensation water to be diverted.
Point-supported façades in countries such as Germany do not belong to the regulated construction products (as to the legal construction regulations) and therefore need approval for construction in each particular case.
18.104.22.168 Membrane façades
A variation of the point-supported façade with drill holes in the glazing was developed in the past several years. Like a tennis racket, the whole façade is strung with a network of steel cables in the grid dimension of the glass panes. The joints of the horizontal and vertical cables are fixed with fasteners, which serve at the same time as fittings for the façade glass in the relevant four corners. The façade affecting loads are transported through these fittings into the cables from where they are conducted into the bearing frame construction. Thanks to the sealing of the joints, similar to the point supported, the network of cables disappears optically behind the glass edges and offers a construction free perspective through the façade. The corner positioning of the glass elements without boreholes avoids increased stress concentrations and enables more free dimensioning. The pre-stressing of the ropes will be done in such a ways that the whole area can be deformed under load and all functions are maintained before the load peaks are conveyed via the vertical ropes into the grounding and the roof frame. This construction needs always an approbation in particular cases.
(Schematic diagram – Guardian?)
8.2 Parapet glass
Parapets are often complete glass panels which hide constructive and functional parts of the building, for example, paving tiles, pillars, heating-, ventilation and air-conditioning elements but also electrical wire ducts and tubes. Therefore opaque parapet glasses are often in front of intermediate ceilings on each floor of a building in the façade and interrupt thereby the transparent glass elements. So the wanted optical aspect can be aligned with the transparent glazing or be contrary. For larger projects it is recommended to make a 1:1 sample presentation to be able to achieve the desired optical appearance in the later façade. The outer parapet is normally a one pane safety glass to avoid thermally influenced glass breakage. The haze of these glasses can be achieved through various production modes depending which optical intentions are to be achieved. Regardless of the production technique, the adhesion and compatibility of the typical colours on the particular float glass coating are important, as well as their pre-tempering capability.
Guardian has broad experience both in coating of float glass and their further processing ability as to bending, pre-tempering, laminating and various colour applications to achieve haze or also translucency. The mostly frequently used colours are ceramic colours which can be coated in different technics on the back side of the pane. Various technics are available, namely, roller coating, spraying, printing or curtain coating.