Curtain Wall System Explained: Components, Types, Design, and Modern Applications

A curtain wall system is a non-structural building envelope that is held from a structural frame around the building. These wall systems allows the buildings to be lighter, taller and transparent compared to conventional brick wall systems. 

The invention of curtain wall system happened to meet the energy crisis and performance in the 70s.  In the 90s the objective was to develop a façade system that act as a engineered climate device with high feasibility and better quality. Today curtain wall system have entered the era of intelligent façade. 

Originally curtain wall system was just a wall barrier, but now its a envelope with environmental interface. 

In this article we will discuss the features of curtain walls, its types and its structural arrangement.

What is a Curtain Wall?

Curtain wall is a non-load bearing wall that protects the interior of the building from the external environment. Unlike other structural walls, they do not take part in transferring load from one beams or columns above to the below structure.

Curtain walls are designed and constructed only to take their own weight and external loads acting on them like wind or seismic loads. These loads are transferred back to the primary structure of the building. Hence, curtain walls are not a part of the primary structure of the building.

Types of Curtain Wall Systems

Curtain wall systems are broadly classified into two main types based on the method of fabrication and installation.

1. Stick Curtain Wall System

Stick curtain wall systems are assembled piece by piece at the construction site. Individual components such as mullions, transoms, and glass panels are transported separately and installed sequentially.

The installation procedure depends largely on site access conditions and project complexity.

Key features:

1. Installed on site member by member

2. Lower initial fabrication cost

3. Requires more site labor and time

4. Suitable for low to medium height buildings

Because most of the work happens on site, the quality control depends heavily on workmanship and supervision.

Fig. (a) Stick Curtain Wall System (b) Unitised Curtain Wall System

2. Unitised Curtain Wall System

Unitised curtain wall systems are pre-fabricated in factory-controlled conditions and delivered to the site as large modular panels.

These panels are lifted and fixed directly to the building structure.

Key advantages:

1. Superior quality control

2. Faster installation time

3. Reduced site labor

4. Better performance in high-rise buildings

Due to factory fabrication, unitised systems generally provide better air and water tightness compared to stick systems.

Components of a Curtain Wall System

A curtain wall system consists of several integrated components that together ensure structural stability, weather resistance, and energy performance.

Components of a Curtain Wall System

1. Framing System

The frame acts as the backbone of the curtain wall. It is typically made of lightweight, high-strength, corrosion-resistant aluminium.

Primary functions of the framing system:

1. Supporting infill panels

2. Resisting wind loads

3. Transferring loads to the main structure

4. Maintaining façade geometry

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2. Mullions and Transoms

Mullions and transoms are the primary framing members of a curtain wall. Mullions are vertical members that transfer loads downward to the structure. Transoms are horizontal members that connect mullions and support infill panels. Their proper design is essential for wind resistance and structural stability.

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3. Infill Panels

Infill panels form the visible outer surface of the curtain wall façade. They are fixed within the framing system and determine the thermal, acoustic, and visual performance of the building envelope.

Common infill panel materials include:

1. Vision glass such as single, double, or triple glazing

2. Spandrel (non-vision) glass

3. Aluminium solid sheets

4. Aluminium Composite Panels (ACP)

5. Honeycomb panels

6. Stone or brick veneer

7. Terracotta panels

8. Fibre Reinforced Plastic (FRP) panels

9. Louvres or ventilation panels

Composite Infill Panels

Many modern curtain wall panels are composite panels. In these systems, facing materials are bonded to or sandwich an insulated core.

Common core materials include:

1. Polyethylene (PE) core

2. Polyurethane (PUR) core

3. Profiled metal core

4. Mineral core

Composite panels improve stiffness, thermal insulation, and overall façade performance.

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4. Anchors and Fittings

Anchors and fittings are the connection elements that secure the curtain wall to the primary building structure. They help the façade safely resist environmental loads.

Main functions:

1. Transferring loads to the structural frame

2. Allowing adjustment during installation

3. Accommodating building movement

4. Ensuring façade stability

Proper anchor design is critical for safety.

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5. Thermal Breaks

Thermal breaks are insulating elements inserted within aluminium framing to reduce heat transfer between exterior and interior.

Without thermal breaks, aluminium frames act as strong thermal bridges, leading to energy loss and condensation.

Benefits of thermal breaks:

1. Improved energy efficiency

2. Reduced thermal bridging

3. Prevention of condensation

4. Enhanced indoor comfort

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6. Seals and Gaskets

Seals and gaskets are flexible components used to prevent air leakage and water penetration through curtain wall joints.

They are commonly made from EPDM rubber, silicone, or similar durable materials.

Key roles:

1. Preventing water ingress

2. Improving air tightness

3. Allowing movement at joints

4. Enhancing acoustic performance

Proper sealing is vital for long-term durability.

Performance Requirements of Curtain Wall Systems

Once the main components of a curtain wall system are in place, the real engineering challenge begins. A curtain wall is not just a decorative skin. It must behave like a carefully tuned environmental shield that responds to wind, rain, temperature changes, and building movement throughout its service life.

A well-designed curtain wall simultaneously satisfies structural safety, thermal comfort, weather tightness, and durability. If even one of these functions is weak, façade performance can deteriorate quickly.

1. Structural Load Transfer

Although a curtain wall does not carry floor loads, it must safely transfer its own weight and all external forces back to the primary structure. Wind pressure is usually the governing load, especially in high-rise buildings.

The framing members, particularly the mullions, act as the main load path. They channel wind forces and panel weight into the anchors, which then pass the forces into slabs or beams. If this load path is not clearly designed, problems such as excessive deflection, glass cracking, or anchor distress can occur.

For this reason, structural checks such as allowable deflection limits and anchor capacity verification are essential during design.

2. Thermal Performance and Condensation Control

Modern buildings demand energy efficiency, and the curtain wall plays a major role in this requirement. Aluminium, while strong and lightweight, is also a very good conductor of heat. Without proper detailing, the frame can become a thermal bridge that allows heat to flow freely between inside and outside.

This is where thermal breaks become critical. By interrupting the metal path, thermal breaks significantly reduce heat transfer and help maintain indoor comfort. Proper glazing selection, such as double glazing or low-E coatings, further improves thermal performance.

Equally important is condensation control. If interior warm air meets a cold frame surface, moisture can form. Good thermal design prevents this hidden but damaging problem.

3. Fire, Smoke and Acoustic Separation

Curtain walls must also function as environmental separators between floors and interior spaces. At slab edges, special perimeter fire barriers are typically required to prevent vertical fire spread through the façade cavity.

In addition to fire safety, the curtain wall contributes to acoustic comfort by reducing external noise transmission. This becomes particularly important in urban high-rise buildings located near traffic corridors or airports.

4. Accommodation of Building Movement

Buildings are never completely still. They expand and contract with temperature changes, sway under wind loads, and may experience inter-storey drift during seismic activity.

A rigid façade would quickly fail under such movement. Therefore, curtain wall systems are intentionally designed with movement joints, flexible gaskets, and slotted anchor connections.

The goal is simple but critical: the façade must move gracefully with the building without cracking glass or tearing seals.

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Curtain Wall Water Control Systems

One of the most frequent causes of curtain wall complaints is water leakage. Wind-driven rain can create significant pressure differences across the façade, pushing water into even tiny gaps.

To address this, modern curtain walls use three main water control philosophies. Understanding their differences is important for both design and troubleshooting.

1. Face-Sealed Systems

In face-sealed systems, the outermost seal is expected to stop all water and air penetration. At first glance, this seems logical. In practice, however, maintaining a perfect seal over years of weathering is extremely difficult.

Small seal imperfections, ageing sealants, or minor installation errors can allow pressure-driven water to enter. Because of this, face-sealed systems are generally considered less reliable for demanding conditions.

2. Water-Managed Systems

Water-managed systems take a more realistic approach. Instead of assuming zero leakage, they accept that some water may pass the outer seal. The design then focuses on safely collecting and draining that water back to the exterior through internal drainage paths and weep holes.

In these systems, drainage becomes the primary defence mechanism. Proper slope, clear weep holes, and unobstructed cavities are essential for performance.

3. Pressure-Equalised (Rainscreen) Systems

Pressure-equalised systems represent the most advanced and reliable strategy used in modern high-performance curtain walls.

In this approach, a ventilated cavity is created between the outer and inner gaskets. This cavity is connected to the exterior so that the air pressure inside the cavity quickly equalises with outdoor pressure. When pressure is equalised, wind cannot force water inward.

Any rain that passes the outer gasket simply drains back outside through vents or weep holes.

Because of their superior resistance to wind-driven rain, pressure-equalised systems are widely preferred for high-rise and exposed buildings.

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Curtain Wall vs Window Wall

Curtain walls and window walls often look similar from the outside, but their structural behaviour is fundamentally different.

A curtain wall is hung from the building structure and typically spans across multiple floors without resting on each slab. It behaves like a continuous exterior skin.

A window wall, in contrast, is installed floor by floor between slabs. Each level supports its own façade segment.

This difference affects performance and application. Curtain walls are generally preferred for tall buildings where wind performance and façade continuity are critical. Window walls are often more economical for mid-rise residential projects.

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Structural Design Considerations for Curtain Walls

Behind every elegant glass façade lies careful structural engineering. Designers must ensure that the curtain wall remains safe and serviceable under all expected loads.

Key aspects that require special attention include:

1. Accurate wind load estimation based on building height and exposure

2. Control of mullion and transom deflection within allowable limits

3. Proper selection of glass thickness and type

4. Robust anchor and bracket design

5. Provision for inter-storey drift in seismic regions

Ignoring any of these factors can lead to serviceability failures long before structural collapse becomes a concern.

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Curtain Wall Installation Procedure

Even the best design can fail if installation is poor. Curtain wall erection therefore follows a carefully sequenced process to ensure alignment, safety, and weather tightness.

A typical installation workflow includes:

1. Site measurement and setting out reference lines

2. Fixing of anchors and support brackets to the structure

3. Installation and plumbing of vertical mullions

4. Fixing of horizontal transoms between mullions

5. Placement and securing of infill panels

6. Installation of gaskets, sealants, and pressure plates

7. Final alignment checks and quality inspection

Strict supervision during installation greatly reduces future leakage and alignment issues.

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Common Problems in Curtain Wall Systems

Despite sophisticated design, curtain walls can develop problems when detailing, fabrication, or maintenance is inadequate.

The most frequently observed issues include:

1. Water leakage at joints or slab edges

2. Glass breakage due to excessive deflection or thermal stress

3. Sealant or gasket deterioration over time

4. Thermal bridging leading to condensation

5. Panel misalignment affecting aesthetics and performance

6. Blocked weep holes preventing proper drainage

Early inspection and preventive maintenance can significantly extend façade life.

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Performance Testing of Curtain Walls

Before acceptance, curtain wall systems are typically subjected to laboratory or on-site testing to verify their performance.

Major performance tests include:

1. Air infiltration testing to measure air tightness

2. Water penetration testing under simulated wind-driven rain

3. Structural load testing for wind resistance

4. Seismic or racking tests where applicable

5. Thermal performance evaluation for energy efficiency

These tests provide confidence that the façade will perform as intended under real environmental conditions.

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Advantages of Curtain Wall Systems

Curtain walls have become the façade of choice for many modern buildings because they offer several practical and architectural benefits.

They provide a lightweight exterior enclosure that reduces structural dead load. They enable large glazed areas that improve daylight penetration and enhance building aesthetics. They also allow faster enclosure of high-rise buildings compared to traditional masonry façades.

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Disadvantages of Curtain Wall Systems

Despite their advantages, curtain walls also present certain challenges that designers and owners must consider.

They typically involve higher initial costs than conventional wall systems. Installation requires skilled labour and precise quality control. Regular maintenance is necessary, particularly for seals and drainage systems. If detailing is poor, the risk of water leakage increases significantly.

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Maintenance and Cleaning of Curtain Walls

Curtain walls require planned maintenance to preserve both performance and appearance over time.

Routine façade care typically involves periodic inspection of seals and gaskets, regular glass cleaning, checking of drainage paths and weep holes, and replacement of damaged panels when necessary.

For tall buildings, dedicated façade access systems such as BMUs or gondolas are usually provided to enable safe inspection and maintenance.

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Latest Trends in Curtain Wall Technology

Curtain wall technology continues to evolve as buildings demand higher energy efficiency and smarter façades.

Current innovations include double-skin curtain walls that improve thermal performance, smart electrochromic glass that controls solar gain, building-integrated photovoltaics that generate power, large-format unitised mega panels for faster construction, and parametric façades that allow complex architectural forms.

These developments are transforming the curtain wall from a passive enclosure into an intelligent building skin.

Read More: High Performance Glass Options for Windows and Doors  

FAQs

1. What is a curtain wall system in construction?

A curtain wall system is a lightweight, non-load-bearing exterior façade that encloses a building and transfers wind and self-weight loads to the main structural frame.

2. What is the difference between curtain wall and window wall?

A curtain wall is hung from the building structure and typically spans multiple floors, while a window wall is installed floor by floor and supported at each slab level.

3. What are the main components of a curtain wall system?

The main components include aluminium framing (mullions and transoms), infill panels such as glass or metal panels, anchors and fittings, thermal breaks, and seals or gaskets.

4. How does a curtain wall prevent water leakage?

Curtain walls prevent leakage using a combination of gaskets, sealants, drainage paths, weep holes, and pressure-equalised cavities that stop or safely drain water.

5. Which is better: stick curtain wall or unitised curtain wall?

Unitised curtain walls generally provide faster installation and better factory quality control, while stick systems may be more economical for smaller or less complex projects.