Last update: 06.08.2019
Building with glass
6.

Facades

Generally, glass façades must be looked at from two perspectives, namely function and construction.

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Façade functions

The façade function describes the mode of operation of the building shell. There are generally three different possibilities:

 

Warm façade

The warm façade describes a single-shell system in which thermal insulation with an interior steam barrier is connected to a glass pane (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 necessary, to keep fire from penetrating into the room. These opaque panels need a four-sided frame in the form of post-and-beam construction.

Suitable glass types are enameled float glass or single glazed SunGuard HD (see Guardian spandrel glass recommendations).

Warm facade

 

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 solar control glass and colour coordinated with the transparent window. 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 achieved by insulating opaque wall areas behind these parapet planes. 

A typical glass type is enameled float glass (see Guardian spandrel glass recommendations).

Cold facade

 

Double skin façade – ventilated systems

Ventilated façades are highly innovative. Their benefits in conjunction with numerous other features are manifold. They include in particular, optimisation with regard to energy management, thermal insulation and above all the dynamic selectivity regarding the inclusion of mechanical sun protection located in the inter space, sound insulation and, last but not least, the possibility of providing ventilation and enhanced comfort.

Types of ventilated façades

There are two systems - active and interactive (passive). The active systems have an outer skin of airtight insulation glass in front of the ventilated inter space. Air exchange is artificially induced and takes place inside the building via heat exchangers. In winter this has the advantage that energy required for heating can be saved via heat recovery. The customary types of glass can be employed for the external insulating glass skin. 

A special type of ventilated system is the so-called “Closed Cavity Façade” (CCF). It provides an encapsulated air space between inner and outer skin but is not hermetically sealed. Dry and clean air is constantly fed into the cavity to prevent condensation forming. The advantage of this system is the significantly reduced effort required for cleaning and maintenance.
 

Types of ventilated façades_Aktive systemTypes of ventilated façades_Interaktive system

 

Interactive (passive) systems

In the case of ventilated façade systems, the interactive systems are by far the most common. The air exchange takes place between the inter space and the environment. A natural convection is created via defined openings usually located above and below the outer glass. Suspended glass walls in front of a conventional construction are also possible, as are punctuated façades with box-type windows that have a fixed or hinged outer glass.

The aim is to reflect a part of the short-wave solar energy directly at the outer glass so that the heat build-up in the inter space is reduced and in turn the thermal load. The use of coatings is particularly beneficial in combination with additional sun and anti-glare protection in the inter space. Acceptable g-values are also achieved when the blinds are operated in a fully retracted or intermediate state. The dynamic selectivity that can be achieved in this manner renders the ventilated system particularly attractive.


While the inner glazing of a passive system is a normal double or triple insulated glass, for the outer single glazing typically a laminated safety glass (often consisting of heat strengthened glass) is used. Its residual load capacity ensures maximum safety in case of breakage.

Interactive (passive) systems

 

Solar control glass in the outer pane

The application of a transparent solar control coating on the ventilated outer pane can significantly reduce the overall solar factor of the system by reflecting a proportion of the short-wave solar radiation already on the most external component before entering the system. The use of mechanical shading can be reduced or the blinds can be even be fully retracted compared to alternative solutions without a sun protection coating. The user therefore has the opportunity to operate the mechanical solar protection more effectively (either open or in intermediate states) without having to fear overheating. As a result, more daylight can enter the room and the user can enjoy the unhindered view from inside to outside for longer. This can contribute significantly to an enhanced comfort factor.


When using the coating facing the ventilated air space it must be durable and suitable for monolithic applications – such as the SunGuard HD (High Durable) series. This offers many possibilities with various types of interlayers such as SentryGlas or EVA without limitations regarding structural performance, compatibility or safety classification.

In the case of facing to the interlayer of laminated glass, the coatings must be compatible with the interlayer material and must be certified according to the relevant standards when safety glass is required. 
Reasons for using SunGuard HD against interlayer can be the reduced outdoor reflection and higher light transmission which leads to an increased spectral selectivity.

The combination of SunGuard HD with solar absorbing PVB interlayers can further improve the solar control performance and particularly the spectral selectivity of the ventilated outer pane. 


For suitable combinations of laminated glass for ventilated systems considering the SunGuard HD range and PVB interlayer.

Condensation

Depending on the position of the building, as well as adverse climatic conditions, condensation may occur on the inner side of the outer glass pane of passive ventilated constructions. Of particular concern are the morning hours in spring and autumn. This can significantly disrupt the clear view from inside.

Solutions against this natural phenomenon are anti-fog-coatings such as Guardian "ClimaGuard Dry". A specially designed, extra-durable coating is applied onto the outer glass pane, which prevents condensation. It is essential to consider the use of this glass in the planning stage because the application of such coating after installation is not possible.

Condensation facades

The anti-fog-coating must be installed on surface #1 (facing outside) of the secondary glazing in order to ensure the best possible functionality.

Tests under real building conditions have shown that this solution provides slightly higher surface temperatures compared to an uncoated outer surface. This temperature difference significantly reduces the appearance of condensation. While the uncoated secondary glazing shows condensation during many hours, under the same conditions the coated glass remains clear and free of water droplets throughout.

Condensation

 

Façade constructions

Joining the glass to the building and the shell is as important as the function.

Stick-System-Façade (Mullion-Transom-System)

The majority of today’s glass facades still consist of post and beam. Here, the load-bearing posts extend from the foundation to the roof of the building in a fixed, aesthetically pleasing manner and at a statically determined and technically feasible distance from each other. These posts are anchored to the building design and transfer all applied loads into it. The “long fields” that therefore react to the top are then intersected by a defined number of horizontal beams 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 beams. 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 are available in almost all anodised colours. These strips primarily influence the outer colour scheme. Stick façades are typically equipped with a dry gasket (rubber profiles).

 

Stick-System-Façade (Mullion-Transom-System)Stick system facade

 

Structural glazing

Definitions

 

A structural glazing façade is designed as an aluminium-adapter-framework glued together with a special insulating glass unit using structural glazing silicones. This aluminium-glass-system is suspended into a conventional curtain wall construction. From the exterior side only, glass and – depending on the system – weather sealant, are visible.

Definitions

Main features:

  • Joining technique appropriate for the material involved.
  • No microstructural change of parts (e.g. welding).
  • Load transferring function.
  • No local stress peaks by planar transfer of forces trough planar adhesive area.
  • Ageing stability of silicone (adhesion, UV resistance, temperature resistance).
  • Safety at extreme mechanical loads (earthquakes, tropical cyclones, explosions, etc.).

A typical structural glazing junction consists of:

  • Structural bonding providing a static effective connection.
  • Insulating glass edge seal adapted on wind and dead loads and with density function.
  • Weather seal.

The structural silicones provide a high sheer and Young’s modulus for compensation or for transferring

  • Dynamic loads (wind suction, wind pressure, traffic loads).
  • Static loads (dead and snow loads).
  • Differences in the thermal dilatations of involved materials such as glass and aluminium.

As structural glazing systems are typically in front of the curtain wall sub-constructions, no profiles cover and protect the sealant materials from UV radiation. For this reason, requirements on UV resistance are very high. Normal insulating glass sealants based on organic polymers such as polysulfide or polyurethane consisting of carbon-carbon and carbon-oxygen bondings do not resist radiation in the range of UV-A. The bondings are destroyed and the sealants lose their mechanical and chemical performance. The Silicon-Oxygen bondings of Silicones have a much higher bonding energy corresponding to the energy of UV-C radiation. This radiation does not reach the surface of our planet under normal conditions.

Compared to organic polymer sealants silicones are also hydrophobic and provide increased flexibility.

Types of structural glazing
Structural step (insulating) glass

Structural step (insulating) glass

  • Structural bonding between glass and sub-construction: metal (e.g. aluminium, stainless steel) or other panel materials.
  • High modulus silicones.
  • Structural functionality and load transfer on the outer pane.
Structural insulating glass

Structural insulating glass

  • Structural bonding between glass and sub-construction.
  • Structural insulating glass sealants.
  • High modulus silicones.
  • Structural IG silicones should never be used as structural glazing adhesives!
  • Structural functionality and load transfer on the outer and inner pane.
Toggle system

Toggle system

  • Structural insulating glass sealants.
  • Screw connection between edge seal (U-profile) and sub-construction.
  • High modulus silicones.
  • Structural functionality and load transfer through edge seal.
Relevant European standards for structural glazing 

ETAG 002 Guideline for European Technical Approval for Structural Sealant Glazing Kits.    
EN 13 022 Glass in building – Structural sealant glazing

  • Part 1:    Glass products for structural sealant glazing systems for supported and unsupported monolithic and multiple glazing.
  • Part 2: Assembly rules.

EN 15 434 Glass in building – Product standard for structural and/or ultra-violet resistant sealant (for use with structural sealant glazing and/or insulating glass units with exposed seals.
EN 1279    Insulating glass.
DIN 18 008 Glass in building - Design and construction rules.

 

Relevant European standards for structural glazing

 

Coated glass in structural glazing applications

According to ETAG 002-1, multifunctional glass (without the approval of a notified body institute for monolithic applications such as SunGuard HP, SunGuard SN and SunGuard SNX or thermal insulating low-E glass such as ClimaGuard) is not suitable for structural glazing. In this case the coating needs to be removed in the concerned areas accordingly. Selected coatings from the SunGuard HD range of products which are suitable for monolithic applications can be used in structural glazing.


Typically, applications with structural bonding need to be tested and approved. If a European certification for structural glazing according to ETAG 002-1 is required, please contact Guardian for detailed information about suitable glass types and tested coating-sealant combinations that comply with ETAG 002-1 requirements.

Another option when using high performance coated architectural glass (SunGuard SN, SNX, HP) in structural applications is “Guardian System TEA”. This is a special enamel system that can be applied directly onto the coated surface. After firing, the coating is completely dissolved and only glass and enamel are left. This system is tested and approved for most Guardian heat treatable SunGuard coatings. The enamel is mechanically and chemically very stable and the optically homogeneous surface provides reliable adhesion for structural applications. Guardian System TEA is tested and certified for various structural sealants according to ETAG 002-1. For detailed information please contact Guardian.

Point supported façade 

This façade technique 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, which 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 contact and fixed with counter panes. These covering and fixing panes project from the surface. An alternative is conical perforations that gain 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 is holding points, which are placed on the level of PVB films and thus form a laminated safety glass, 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 account for the allowable deformation of the panes and the flexibility of the fittings. The stresses arising from loads are induced through the holding buttons without any restraint into the load bearing construction. The joints between the individual glass façade elements are sealed with UV-resistant closing systems. In this way, attached façades out of monolithic glasses can be built, as well as insulating glazed 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 are not regulated construction products (in terms of legal construction regulations) and therefore need approval for construction in each particular case.
 

Point supported facadePoint supported facade

 

Membrane façade

In the last few years, a variation of the point-supported façade with drill holes in the glazing has been developed. Like a tennis racket, the whole façade is strung with a network of steel cables in a grid dimension of the glass panes.

 

Membrane facadeMembrane facade

The joints of the horizontal and vertical cables are fixed using fasteners, which also serve at the same time as fittings for the façade glass in the relevant four corners. Loads affecting the façade are transported through these fittings into the cables from where they are conducted into the bearing frame construction. Due to the sealing of the joints, similar to a point supported design, the network of cables disappears optically behind the glass edges, offering a construction-free perspective through the façade.


The corner positioning of the glass elements without boreholes avoids increased stress concentrations and enables greater dimensional freedom.

 

Membrane facade

 

Pre-stressing of the ropes is achieved by ensuring 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 requires approval in each individual case.