1. What is a framed-type glass curtain wall?

The glass curtain wall supported by a metal frame around the glass panel is called a frame-type glass curtain wall. It generally uses aluminum alloy and steel profiles to fix the glass and various effects.

2. How many types of framed type glass curtain walls?

From the external form of the curtain wall, it includes
exposed frame glass curtain wall
semi-hidden frame glass curtain wall
hidden frame glass curtain wall

Divided by the installation method, it has
unitized curtain walls
stick system curtain walls

The glass used in these glass curtain walls includes tempered glass, laminated glass, insulating glass, coated glass, etc.

1. Exposed frame glass curtain wall

The exposed frame glass curtain wall has fixed glass horizontal and vertical metal profiles exposed on the outer surface. The original profiles are all functional products with a square form. However, to enhance their decoration, many manufacturers have developed a variety of cross-sectional shapes with facade decoration functions for design selection. Metal frames come in various forms due to metal materials, colors, and surface processing techniques.

exposed frame glass curtain wall

2. Semi-hidden frame curtain wall

A semi-hidden frame curtain wall is a structural glue bonded glass curtain wall. Structural glue bone the glass to the metal frame to form a small plate unit in the glass factory. Then the plate unit is suspended and fixed on the metal supporting structure after being transported to the construction site. The structural glue plays a role in setting the glass, resisting horizontal wind load, and even bearing the gravity of the glass. This curtain wall type has a horizontal or vertical fixed metal component of the glass exposed on the outer surface. Structural glue bonds the other direction. So the joint action of metal profiles and structural sealant fixes the glass.

semi hidden frame curtain wall

3. Hidden frame curtain wall

A hidden frame curtain wall is a curtain wall where all four sides of the glass are by glue bonding. In this way, from the curtain wall’s outer surface, we can only see the glass and glue joints. And the metal frame is entirely behind the glass panel. As a result, the appearance of this kind of curtain wall is more concise, and there are no redundant details. It became popular in the United States in the 1960s. The most famous one was the Pacific Design Center (Blue Whale), designed by César Pelli.

hidden frame glass curtain wall

In the beginning, most of the structural glue-bonded curtain walls used high-reflectivity coated glass. As a result, most architectural appearances were simple blocks, which would look dull for a long time and produce light pollution. Nowadays, architects rarely use this relatively closed and boring curtain wall. Instead, they prefer to use high transparency and low reflectivity glass to provide a richer visual experience.

Since the hidden frame curtain wall relies on structural glue to fix the glass, the requirements for structural sealant are very high. In addition, its durability plays a vital role in the safety of the curtain wall. Therefore, the curtain wall adopting this mode must choose qualified structural glue (with the manufacturer’s quality assurance certificate) and a high-level construction team. Silicone structural adhesive has about 40 years of history. However, the manufacturers generally provide only a 10-year warranty for legal reasons, but its actual life should be 30-50 years. In addition, some countries have strict regulations on glue-bonded glass curtain walls for safety. For example, the German laws require additional mechanical fixation for parts below 8m above the ground if it exceeds this range.

4. Two sides fixed frame glass curtain wall

The glass panels of the conventional frame-type glass curtain wall are fixed all around (adhesive bonding or frame support fixing). In addition, there are particular forms in some designs where only two sides support and set the glass panels.

In these cases, the upper and lower sides fix the glass panels, and the fixed side is generally the long side direction of the glass panel. This kind of glass curtain wall has no vertical columns or a distance between the vertical columns and the surface of the curtain wall.

The upper and lower sides of the glass panel are fixed on the metal beam in the horizontal direction of the exposed frame or hidden frame glue. The other two sides of the glass panel (in the vertical direction) are directly sealed with glass glue and even left as an open seam. (When the curtain wall is required to be airtight).

This glass curtain wall reduces the contact between the metal profile and the glass surface. It is more transparent and novel than the conventional frame-type curtain wall, and the horizontal lines are more prominent. Therefore, it is more suitable for the glass with high transparency.

In addition, there are also left&right sides fixed types of curtain walls. This type must carefully consider how the structure overcomes the long-term gravitational influence of the glass panel.

5. Stick System Curtain Wall

The curtain wall installation methods are stick system, unitized type, and semi-unitized curtain wall. First, install metal columns on the main structure for stick system curtain walls, then beams and glass panels. Unfortunately, this construction mode requires a lot of work on-site and relatively tricky quality control.

6. Unitized curtain wall

The unitized curtain wall system assembles the components and facing materials into a unit in the factory. After that, the whole team will transport to the construction site for hoisting pre-installed the main body of the building structure. Then, when fixing, the unit adopts the plug-in form and fine-tune it to complete the installation process of the entire curtain wall.

BnF National Library of France / Dominique Perrault

BnF National Library of France / Dominique Perrault

The main features of the unit curtain wall are:

  1. The curtain wall unit blocks assembled in the factory workshop, with high processing accuracy and easy to ensure the engineering quality of the wall. Still, the transportation and storage costs are relatively high.
  2. The unitized curtain wall structure adopts the principle of equal pressure. Combined with the specially designed rubber sealing strip, it has good performance in preventing rainwater leakage and air permeability.
  3. On-site installation is fast and straightforward, which is beneficial to shorten the overall construction period of the building.
  4. A plug-in connection connects the plates, adapting to certain deformations and having solid seismic resistance.
  5. Unique anti-aging rubber strips sealed the joints. As a result, the curtain wall has an excellent self-cleaning function. As a result, the surface is less polluted, and the effect is more refined than glue joints.
  6. High technical force, equipment, and management requirements increased requirements for the position and installation accuracy of the embedded parts of the structural wall.
  7. The cross-sectional shape of the metal profile is relatively complex, so the overall price is higher than that of the conventional frame-type curtain wall.

The apparent effect of the exposed frame glass curtain wall is not significant whether it adopts the unit type or the component type. Still, the difference is huge for the entirely hidden frame glass curtain wall. Since the unit curtain wall generally adopts the plug-in method, the hidden frame curtain wall joints are usually concave. So the appearance effect is more refined, and the lines are more straight.

7. Other forms of framed curtain walls

There are also frame-type curtain walls with external glass ribs. The function of glass ribs is to serve as components that bear horizontal loads, reduce the cross-section of the metal profile, enrich the building facade, and improve sound insulation effects. Of course, the structural design of the frame-type curtain wall with external glass ribs is more complicated. The main subject is to solve the problems of glass rib bearing and horizontal wind load to avoid the glass ribs becoming a burden on the curtain wall structure condition.

Sony Center Berlin / Murphy Jahn

Sony Center Berlin / Murphy Jahn