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A Brief Guide to Curtain Wall Systems

Curtain wall systems are considered to be one of the most important elements of facade technology in the modern-day high rise buildings. Facades create the exterior envelope of a building with components such as cladding elements, window wall, curtain walls, etc.

Functionally speaking, curtain walls are non-structural cladding systems that separate the building’s exterior from the interior, while supporting its own weight and the imposed seismic load, wind load, etc.  Curtain wall systems typically comprise of opaque or glazed infill panels fitted onto a lightweight aluminium frame.

These days, curtain walls have a significant structural importance, similar to the building’s other structural elements.  As these systems are exposed to the exterior atmosphere, proper design, installation, and maintenance is important to ensure their sustainability and functionality.

Let us now take a look at some of the most important functions of a curtain wall.

Functions of Curtain Walls:

  • One of the most fundamental functions of a facade is to prevent water penetration. In general, curtain walls utilise a two stage prevention system. The primary level provides complete defence against water. If this system fails, a secondary level of protection directs the percolated water to be drained off.
  • A critical environmental function of curtain walls is to minimise carbon dioxide emission resulting from the rate of gain or loss of heat within the internal or external environment.
  • The cladding systems are responsible for transferring wind actions to the floors of the buildings that function as the linear support. Cladding systems made of large panels are generally one-way spanning. Therefore, each floor level is capable of supporting a wind load of one level on the building.  In order to reduce energy consumption and CO2 emissions, thermal insulation is also performed by facade systems. This task is accomplished by using insulating materials in both transparent as well as opaque areas. In city centred buildings, curtain walls also provide acoustic insulation between the outside and inside environment.
  • Selective solar control coatings are often used on one of the glass surfaces to reduce the solar levels. These coatings allow selective solar radiation wavelengths to pass through. Compared to infrared wavelengths, the visible light wavelengths are allowed to pass through.

Curtain Wall System Types:

These factory pre casted systems are transported to the site and assembled. Depending on the way their components are assembled, curtain wall systems can be categorised as sticked and unitised curtain wall systems.

Stick curtain wall systems require piece by piece assembly of its components at the site on the building. These systems are installed mostly in low rise buildings because exterior access is required for reaching higher elevations. This demands the use of cranes, scaffolding, etc. As onsite adjustments are possible, these systems have low shipping cost. However, the labour consumption and time required is generally high.

The assembly of unitised curtain wall systems involve interlocking units sourced from the factory. Installation of each component individually is not required here because the components arrive together as a single unit. The building’s floor to floor height determines the size of the unitised curtain walls. These systems are extensively used in high rise buildings, and do not require scaffolding, cranes, or any other type of external support.  Higher quality and faster construction are two advantages of these systems. However, the shipping charge can be considerably higher compared to stick systems.

Curtain Wall Components:

Transom, mullions, vision glass, and anchor are the four primary components of a curtain wall system. Transoms are the horizontal rails in a curtain wall panel. On the other hand, mullions or vertical rails remain anchored to the beam or edge slab. The components are primarily responsible for supporting a curtain wall’s dead weight. Each of the systems is placed one after another in a sticky curtain wall system. This installation process requires thorough quality check and high precision. However, in case of unitised systems, installation only requires connecting the two units sourced from the factory.

Panel Framing:

Unitised systems are often characterised by split transoms and mullions that are evident in the panel perimeters. However, no such splits are found in sticky curtain walls. Intermediate transoms are required during longer spans to split the vertical panel in two parts.  Transoms and mullions are thermally broken to prevent condensation, eliminating the probability of cold bridging.

Support Conditions:

Curtain walls are hung from the top of a building and supported laterally at different floor levels. The edge beams are responsible for holding most of these supports. Therefore, in order to avoid larger deflections, it is essential to have edge beams that are highly stiffened. Provisioning for proper edge beam prevents the curtain wall and cladding systems from damage, particularly if the system is highly glazed.

Structural Behaviour:

As one of the structural elements of a building, curtain walls function as a barrier between the building’s exterior and interior environment. Therefore, it has a significant role in ensuring structural stability by transmission of loads.

In addition to transmitting wind induced loads, these systems are also capable of resisting the seismic accelerations and gravity loads. Curtain walls also provide resistance against water penetration and adapt to different ranges of temperature.

These were just some preliminary discussions related to curtain wall systems. If you want to find out more about your curtain wall or facade, please contact our experts are CGS Facade Group. Over the last fifteen years, we have created numerous highly functional window walls, cladding systems, curtain walls, glass structures, and double-skin façades all over the world.