How should an architect think about façade systems at concept stage?

Choosing a façade system is rarely just a question of appearance.

At concept stage, the decision affects the building’s visual language, glazing proportions, structural strategy, installation methodology, interfaces, and ultimately how the façade performs as part of the building envelope.

Three terms frequently enter the conversation: curtain wall, window wall and structural glazing.

They are not interchangeable.

And within curtain walling itself, there are different system approaches—from conventional stick-built systems to unitized façades and structurally glazed solutions.

Window Wizard’s curtain walling range includes SL60, W75U, SL50, SG50 and Unitized Façade systems, giving specifiers different approaches to consider depending on the architectural and project requirements.

This guide breaks down the terminology in plain language, so the distinction is easier to understand before detailed specification begins.

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First: What Is a Curtain Wall?

A curtain wall is a non-load-bearing façade system that is supported by the building’s structural frame.

Instead of the building relying on the façade to carry its primary structural loads, the curtain wall is attached to the structure and transfers relevant façade loads—such as wind loads and the weight of its components—back to the building.

A conventional curtain wall typically consists of:

• Vertical mullions
• Horizontal transoms
• Glass or other infill panels
• Pressure plates and/or cover caps, depending on the system
• Flashings, gaskets, seals and associated components
• Anchoring and fixing systems

The architectural benefit is flexibility. Curtain walling can create large glazed elevations while allowing the architect to control the rhythm of mullions, transoms and panels.

AluK’s curtain wall range, for example, includes both conventional systems such as the SL50 and SL60 and unitized systems such as the W75U.

The important point is that “curtain wall” describes a façade system category, not one single construction method.

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1. Curtain Wall vs. Window Wall

This is one of the most important distinctions to make at concept stage.

Curtain wall

A curtain wall generally forms a continuous façade in front of the building’s structural floor slabs.

The mullion-transom framework is anchored back to the structure, and glazing or other infill is installed within that framework.

Window wall

A window wall is generally designed as an infill system between the structural slabs or columns of a building.

Instead of creating one continuous façade that passes in front of the slab edges, the system typically sits within the floor-to-floor opening.

This creates a different architectural expression.

You may see:

Curtain wall

Floor slab | façade | Floor slab | façade

versus:

Window wall

Floor slab → window system → Floor slab

The distinction becomes particularly important in buildings where the slab edge, spandrel zone, fire stopping, insulation and façade interfaces need to be coordinated carefully.

Why does the distinction matter?

Because the façade system affects the way the architect resolves:

• Floor-to-façade interfaces
• Spandrel zones
• External appearance
• Glazing continuity
• Thermal and weathering interfaces
• Fire and compartmentation requirements
• Installation sequence
• Interior-to-exterior junctions

There is therefore no universal rule that one approach should replace the other.

The appropriate system depends on the building’s structural design, façade geometry, performance requirements, construction methodology and architectural intent.

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2. What Is Structural Glazing?

Structural glazing is primarily an appearance and fixing approach within a glazed façade, rather than simply a completely separate category from curtain walling.

This distinction is often misunderstood.

A structurally glazed façade can still use a curtain wall framework behind the glass.

The difference is in how the glass is retained and how much of the framing remains visually expressed from the exterior.

In a conventional curtain wall, you may see:

Glass → pressure plate → cover cap

This creates a more visibly framed façade.

With structural glazing, the external appearance can be much cleaner because the glass is structurally bonded or mechanically retained within the system, depending on the specific solution.

AluK describes its SG50 as a structurally glazed curtain wall system using the same mullion and transom grid as its SL50, while allowing a more “all-glass” architectural appearance.

That is an important distinction:

Structural glazing does not necessarily mean there is no curtain wall behind the glass.

In many systems, the curtain wall remains the underlying structural framework.

The difference is how the glazing is integrated with that framework and how the façade is intended to appear externally.

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3. The Three Approaches at a Glance

Approach	Basic idea	Typical visual language	Key concept
Curtain Wall	Continuous non-load-bearing façade attached to the structure	Expressed or controlled grid	Façade framework
Window Wall	Glazed infill positioned between structural floor zones	Floor-to-floor / bay-by-bay expression	Infill between structure
Structural Glazing	Glazing integrated with a curtain wall or specialist support system to reduce visible external framing	Cleaner, more continuous glass appearance	Glazing retention + architectural expression

These categories should not be treated as a simple “better/worse” hierarchy.

The real question is:

What does the building require from its façade?

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4. Understanding Window Wizard’s Curtain Walling Range

Window Wizard’s curtain walling range includes SL60, W75U, SL50, SG50 and Unitized Façade systems.

These systems represent different ways of approaching the relationship between the building structure, façade framework, glazing and installation methodology.

SL60 — Conventional Curtain Walling

The SL60 is a conventional curtain walling system based around mullions and transoms.

AluK describes its SL60 system as having 60 mm mullion and transom widths, with applications including vertical curtain walls as well as sloping façades, roofs, domes, tunnels and polygonal constructions.

For a specifier, the important concept is straightforward:

A conventional framed curtain wall gives you a structured façade grid.

The visible rhythm of verticals and horizontals becomes part of the architectural language.

That can be useful where the design intentionally expresses the façade framework rather than attempting to make the building read as a continuous sheet of glass.

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SL50 — A More Compact Conventional Curtain Wall

The SL50 follows the same basic curtain wall principle, using mullions and transoms, but with a 50 mm frontal dimension.

AluK describes SL50 as a conventional curtain wall system suitable for vertical, inclined and polygonal façades, with options for different glass-retention and opening configurations.

In conceptual terms:

SL50 = conventional curtain walling with a 50 mm façade grid.

The system can accommodate different project conditions and architectural configurations, so the final specification still needs to be developed around the project’s structural, glazing, environmental and regulatory requirements.

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5. SG50 — When the Façade Needs a More Glazed Expression

The SG50 uses the same basic mullion and transom grid as the SL50, but introduces a structurally glazed approach.

According to AluK, the system can be used as a fully structurally glazed solution or combined with an expressed external cover in vertical or horizontal planes.

That gives the architect an important design choice.

You can decide how much of the underlying façade structure should remain visually apparent.

In broad terms:

SL50 → more visibly framed expression

SG50 → more continuous glazed expression

The choice therefore becomes part of the façade design—not simply a technical afterthought.

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6. W75U — Unitized Curtain Walling

Unitized curtain walling changes the way the façade is manufactured and installed.

Instead of assembling the entire façade framework progressively on site, unitized systems use prefabricated façade units that are assembled and glazed before arriving at the installation location.

AluK’s W75U is a 75 mm unitized curtain walling system designed for modern high-rise applications. Its system description includes male-female unit assembly, concealed drainage and a three-barrier gasket arrangement.

This is an important distinction:

Stick-built curtain walling is assembled substantially on site.

Unitized curtain walling relies much more heavily on factory fabrication and pre-assembly.

That difference can influence:

• Site logistics
• Installation sequence
• Programme
• Access requirements
• Quality-control processes
• Façade repetition
• Building height and scale
• Tolerance coordination

AluK specifically positions W75U for applications including tall multi-storey offices, hospitals and schools.

The right decision therefore requires looking beyond the elevation drawing and understanding how the façade will actually be delivered.

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7. Unitized Façade — Designing for Prefabrication

A unitized façade takes the prefabrication principle further.

AluK’s unitized façade system, for example, describes façade frames that are produced and glazed in the factory before being installed at site. Its AW86 series includes both structurally bonded and mechanically retained glazing variants.

For the architect and project team, this changes the conversation.

Instead of asking only:

“What should the façade look like?”

the team also needs to ask:

“How should this façade be manufactured, transported, sequenced and installed?”

That is why façade specification needs to begin early.

A system that looks straightforward in elevation may involve very different fabrication, logistics and installation requirements.

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8. How Should an Architect Approach the Decision?

Rather than beginning with a product name, start with the project requirements.

01 — Start with the architecture

What is the façade supposed to communicate?

Is the design based around:

• A visible structural grid?
• Large uninterrupted glazed surfaces?
• Repeated floor-to-floor modules?
• Deep horizontal bands?
• Sloping or faceted geometry?
• A more minimal external expression?

The desired architectural language should inform the system discussion.

02 — Understand the building structure

The relationship between the façade and the structural frame is fundamental.

Consider:

• Floor-to-floor heights
• Slab edges
• Structural grid
• Column positions
• Movement
• Façade zones
• Opening requirements

The façade should be developed in coordination with the structural design rather than treated as an isolated package.

03 — Consider performance requirements

The final façade specification may need to address:

• Wind loads
• Air infiltration
• Water penetration
• Thermal performance
• Solar control
• Acoustic requirements
• Glass safety
• Fire considerations
• Structural movement

The appropriate values cannot be selected generically. They need to be established for the particular building, location, geometry and applicable standards.

AluK’s own guidance similarly emphasises that façade solutions need to be matched to the requirements of the individual project rather than treated as a one-size-fits-all decision.

04 — Think about installation before construction begins

A façade system can look excellent in a drawing and still present significant challenges if installation methodology has not been considered.

Ask:

How will it arrive?

How will it be lifted?

Where will it be stored?

How will it be accessed?

How will tolerances be managed?

How will interfaces with other trades be coordinated?

For unitized systems in particular, prefabrication changes the relationship between factory production and site installation.

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9. There Is No Single “Best” Façade System

This is perhaps the most important point for a specifier.

Curtain wall, window wall and structural glazing solve different architectural and construction problems.

And even within curtain walling, conventional stick-built and unitized approaches involve different considerations.

The decision should therefore come from the intersection of:

Architectural intent
+
Structural conditions
+
Performance requirements
+
Building height and geometry
+
Installation methodology
+
Programme and project constraints

The product should follow the requirement—not the other way around.

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A Specifier’s Concept-Stage Checklist

Before moving from concept design into detailed façade specification, ask:

Architecture

• What visual language does the façade need?
• How much framing should remain visible?
• What glazing proportions are intended?

Structure

• Where are the slab edges and primary structural supports?
• What movements need to be accommodated?
• What façade loads need to be considered?

Performance

• What are the required air, water and wind criteria?
• What thermal and acoustic performance is required?
• What glazing configuration is appropriate?

Construction

• Is a stick-built or unitized installation methodology more appropriate to the project?
• What are the site access and lifting constraints?
• How will façade interfaces be coordinated?

Detailing

• How will corners, junctions and transitions be resolved?
• How will doors and opening elements integrate?
• How will the façade meet adjacent materials?

These questions help move the conversation from “Which window looks right?” to “Which façade system is appropriate for what this building needs to achieve?”

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The Takeaway

For architects, the most useful distinction is not simply between product names.

It is between different façade strategies.

Curtain walling provides a continuous non-load-bearing façade framework.

Window wall approaches the façade as an infill condition between structural zones.

Structural glazing changes the relationship between the glazing and the visible façade framework to create a more continuous glazed expression.

And within curtain walling, systems such as SL60, SL50, SG50, W75U and Unitized Façade offer different approaches to façade geometry, visual expression and construction methodology.

The right starting point is therefore the project itself.

What is the building trying to achieve?

Once that is clear, the façade system can be selected, detailed and executed around it.

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Share this guide

If you’re an architect, designer, façade consultant or developer working through façade options at concept stage, share this guide with your project team on LinkedIn or Threads.

The earlier the façade conversation starts, the more effectively architecture, performance and execution can be considered together.

Window Wizard
Crafting Views. Enhancing Spaces.

www.windowwizardbuild.com

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