Curtain Wall Construction Explained

A curtain wall is the lightweight, non-load-bearing external facade — usually of glass and aluminium — that hangs off the front of a modern building like a skin. The sleek glazed towers of any city skyline are clad in curtain walls. The defining feature is in the name: the wall is a “curtain” that carries none of the building’s floor or roof loads. It supports only its own weight and the wind pressure on it, transferring those forces back to the structural frame.

This article explains how a curtain wall works, the main construction systems, what it has to keep out, and why the facade is its own demanding engineering discipline rather than a simple cladding job.

What makes it a curtain wall

In traditional construction, the external walls carry load — the floors and roof rest on them. A curtain wall does the opposite. The building’s frame of columns, beams and floors carries all the structural load, and the curtain wall is hung from the edge of each floor, spanning between floors as a thin envelope. Because it carries no building load, it can be light and largely transparent, which is why curtain walls enable the fully glazed appearance of modern buildings.

The forces a curtain wall does carry are its own weight (dead load) and the wind acting on its large surface — both pressure pushing it in and suction pulling it out. These are delivered back into the structural frame at each floor. The distinction between a curtain wall and a load-bearing wall is fundamental, and it connects to the broader topic of load-bearing walls.

Stick and unitised systems

Curtain walls are built in two main ways:

Stick systems are assembled piece by piece on site — the vertical and horizontal aluminium members (mullions and transoms) are installed first, then the glass and infill panels are glazed into the grid. Stick systems are flexible and suit smaller or irregular facades but are slower and depend heavily on site workmanship.
Unitised systems are assembled into large, complete panels in a factory, delivered to site, and hung onto the building floor by floor. They are faster to install, give more consistent quality, and reduce work at height, which is why they dominate tall buildings.

The choice between them depends on the building’s height, the facade’s complexity, the programme and the quality demanded. Unitised construction brings the same factory-quality and speed benefits seen in precast concrete construction, applied to the facade.

What a curtain wall has to keep out

A facade is not just a skin to look through; it is an environmental barrier that has to manage several things at once:

Water. Keeping wind-driven rain out of the building is one of the hardest tasks, handled through carefully designed joints, seals and drainage paths within the system.
Air. Limiting air leakage for comfort and energy performance.
Wind. Resisting the pressure and suction described above without excessive deflection or glass failure.
Heat and solar gain. Managing the sun’s heat through the glass to keep the building comfortable and efficient — particularly important in a tropical climate.
Movement. Accommodating the building’s structural movement and thermal expansion without the facade cracking or leaking.

Of these, water-tightness and accommodating movement are where most curtain wall problems arise, and both depend on getting the joints and seals right. This puts curtain walls squarely within the discipline of facade engineering.

Movement, deflection and the frame behind it

A curtain wall is fixed to a structure that moves. Floors deflect under load, the building sways slightly in wind, and materials expand and contract with temperature. If the facade were rigidly fixed, this movement would crack the glass and break the seals. So curtain walls are designed with movement joints and flexible connections that let the facade and the structure move relative to one another without distress.

This is why the design of a curtain wall cannot be separated from the behaviour of the frame it hangs on. The deflection of the floor edges, the building’s sway, and the design of the brackets that tie the facade back all have to be coordinated. It is genuinely an engineered system, not a finish chosen from a catalogue.

Maintenance, inspection and safety

Because curtain walls are large, exposed, and located high above the public, they need maintenance and periodic inspection over the building’s life. Seals weather, fixings can loosen, and glass and panels must remain secure. In Singapore, the safety of building facades is taken seriously through periodic facade inspection requirements, covered in periodic facade inspection, which exist precisely because a failed facade element can fall and endanger people below.

Specifying, assessing or remediating a curtain wall is specialist work that combines structural understanding with knowledge of weatherproofing and materials. If you are responsible for a building with a glazed facade and need an independent view on its condition or design, our structural engineering consultancy can help.

Frequently asked questions

What is a curtain wall?

A curtain wall is a lightweight, non-load-bearing external facade, usually of glass and aluminium, that hangs off a building’s structural frame and carries only its own weight and wind load, not the building’s floor or roof loads.

How is a curtain wall different from a load-bearing wall?

A load-bearing wall carries the weight of floors and roof above it, while a curtain wall carries no building load at all; the frame behind it does that, and the curtain wall only supports itself and resists the wind acting on it.

What is the difference between stick and unitised curtain walls?

Stick systems are assembled piece by piece on site and suit smaller or irregular facades, while unitised systems are made into complete panels in a factory and hung on floor by floor, giving faster installation and more consistent quality on tall buildings.

What does a curtain wall have to protect against?

A curtain wall must keep out wind-driven rain and air, resist wind pressure and suction, manage solar heat gain, and accommodate the building’s movement and thermal expansion without cracking or leaking.

Why do curtain walls need periodic inspection?

Because they are large, exposed elements high above the public, their seals weather and fixings can loosen over time; periodic facade inspection ensures the glass and panels remain secure so that no element can fall and endanger people below.

Need an independent view on a glazed facade’s design or condition? Talk to our consultancy or get in touch.