Curtain walls are non-structural elements added to a building to provide protection from the elements such as weather and wind. Because the curtain wall does not actually support the construction of a building, it can feature lightweight materials such as glass.

Curtain walls work to deflect water, wind, seismic, and blast loads. Their purpose is to protect a building from all elements including weather, wind, and earth activity. They also contribute to the appearance of a building and are therefore designed with style in mind.

Benefits
When they feature glass, curtain walls provide an infusion of natural light into a building or space, enhancing the overall appearance of the space and decreasing the need for overhead lights during the daytime hours.

Curtain walls work to diffuse wind loads, transferring horizontal loads.

Construction
Curtain walls are designed to span multiple floors at once and are therefore very popular in high-rise buildings in urban areas.

Curtain walls are designed to resist water or air penetration. They are also designed to resist any motion induced by wind or seismic activity. Curtain walls must remain stable across conditions and are therefore also designed to accommodate for thermal expansion and contraction.

Systems
Curtain walls typically employ one of the following systems.

Unitized System: Unitized systems are fabricated in a factory and often employ factory glazing. The costs on such systems tend to be lower than pieces that are fabricated and installed on site.

Stick System: A stick system features long framing pieces between floors on the vertical plane and between vertical members on the horizontal plane. Although the framing pieces in such systems may be fabricated off site, installation and subsequently glazing is typically performed at the building site.

Materials
In their infancy, curtain walls were constructed of steel, however, typical modern construction of curtain walls features extruded aluminum members.

Drawbacks
Light entering a space readily through windows can affect the thermal environment of the space, creating heat and necessitating air conditioning systems be put into full force, particularly in the summer months when sunlight is most direct. However, for most buildings, the benefits of natural light entering the space outweigh the effects of this increase in heat.

Considerations
Curtain wall design takes into consideration environmental concerns such as:
• Thermal efficiency
• Lighting
• Water diversion
• Thermal expansion and contraction

To be successful, a curtain wall must be able to support the following loads and therefore, design must account for all of them:
• Dead load: the weight of the building
• Wind load: the energy that the building must withstand due to wind
• Seismic load: the energy that the building must withstand due to seismic activity
• Snow load: this is only an issue when a curtain wall is sloped at an incline of more than twenty degrees
• Thermal load: Expansion and contraction of the horizontal and vertical mullions must be accounted for in the design of a curtain wall
• Blast load: a curtain wall must be able to withstand bombs and other terrorist-related attacks.