Curtain wall system comprises one of the elements of facade technology in high rise building. Facades involves window wall, cladding elements and curtain walls which generates the exterior envelope of the building.
The curtain wall systems now possess structural importance equivalent to that gained by other structural elements of the building. As it has a higher exposure to exterior atmosphere, it has to be properly designed, installed and maintained keeping in mind the functionality and sustainability.
Fig.1: Curtain Wall System
Fig.2: Curtain Wall Construction
- Functions of Curtain Walls in Buildings
- Types of Curtain Wall System
- Components of a Curtain Wall
Functions of Curtain Walls in Buildings
Elimination of Water PenetrationWater penetration is the fundamental function of a facade. Here bringing a completely impermeable sealed curtain panel system is not possible. Hence two stages of prevention are placed. Primary level where complete defense of water is conducted and if that fails a secondary level where a direction to let percolated water to drained out has to be provided.
Air impermeabilityThis function is more of an environment concern to reduce the emission of carbon dioxide due to rate of heat loss or gain within the external and internal environment.
Resistance to wind, thermal and acoustic actionWind actions are transferred by the cladding system to the building floors which act as a linear support. Building cladding systems formed of large panels are usually one-way spanning. Each floor level therefore supports one level of wind load on a building. Thermal insulation function which is strictly necessary for a facade in order to reduce energy consumption and CO2 emissions. Insulated materials are provided to both opaque as well as transparent areas. Acoustic Insulation too is necessary between the inside and the outside environment mainly city centered building. Massive structural elements possess higher acoustic insulation like masonry or concrete structures.
Solar levelsThis can be reduced by providing a selective solar control coating on one of the surfaces of the glass. This coating is called selective because solar radiation of different wavelengths is selectively allowed to pass through the coating: visible wavelengths of light are allowed to pass more freely than infrared wavelengths. For example, spaces for exhibitions or displays of materials can undergo degradation due to ultraviolet radiation. For this a UV-inhibiting film can be applied to the surface of glazing.
Types of Curtain Wall SystemCurtain wall systems are factory pre casted systems. They are bought to the site and assembled. These are of two types based on the way each component is assembled.
- Stick Curtain Wall System
- Unitized Curtain Wall System
Components of a Curtain WallThe complete unit consist of the following structural elements
- Vision Glass
Fig.3: Detailed Components of a Curtain Wall System
Fig.4: Mullions and TransomsTransom or horizontal rails are horizontal members on the curtain wall panel. The mullions or vertical rails are anchored to the edge slab or beam. These are mainly involved in supporting the dead weight of the curtain wall. In conventional or sticky curtain wall system each system has to be placed one after the other. High quality check and precision in required for the installation. But in unitized system the factory product comes as two units alone which has to connected.
Panel Framing details of Curtain WallsUnitized system is identified by the split mullions and the transforms that are evident in the panel perimeters as shown in figure.5.
Fig.5: Unitized Curtain WallIn case of sticky curtain wall, there is no sort of splits all forms a single unit. During Longer spans, there will be a need for intermediate transom which would essentially split the entire vertical panel into two. In order to prevent condensation, mullions and transom are thermally broken. This prevents cold bridging.