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.
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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
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.
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?”
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.
Curtain Wall FAQ
What is the difference between a curtain wall and a window wall?
A curtain wall forms a continuous, non-load-bearing façade in front of the building’s floor slabs, anchored back to the structure. A window wall is an infill system that sits between the slabs or columns, within each floor-to-floor opening. The choice affects how slab edges, spandrel zones, fire stopping, insulation and façade interfaces are detailed.
Is structural glazing different from a curtain wall?
Not entirely. Structural glazing is mainly an appearance and fixing approach, and a structurally glazed façade can still use a curtain wall framework behind the glass. The difference is how the glass is retained and how much framing is visible from outside. AluK’s SG50, for example, uses the same mullion and transom grid as the SL50 but gives a more continuous, all-glass appearance.
What is the difference between stick-built and unitised curtain walling?
A stick-built curtain wall is assembled largely on site from mullions, transoms and infill panels. A unitised curtain wall uses façade units that are fabricated and glazed in the factory before installation. This affects site logistics, installation sequence, programme, access, quality control and tolerance coordination, which is why unitised systems such as AluK’s W75U are positioned for tall multi-storey buildings.
Which curtain wall systems does Window Wizard offer?
Window Wizard’s curtain walling range includes the SL60 and SL50 conventional curtain walls, the SG50 structurally glazed system, the W75U unitised system and a Unitised Façade system (AluK AW86). Each offers a different approach to façade geometry, visual expression and construction method.
How should an architect choose a façade system at concept stage?
Start with the project’s requirements rather than a product name. Consider the architectural intent, the building’s structure (slab edges, floor-to-floor heights, movement), performance needs such as wind loads, air and water tightness and thermal and acoustic needs, and how the façade will be delivered, lifted and installed. There is no single “best” system; the product should follow the requirement.
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The earlier the façade conversation starts, the more effectively architecture, performance and execution can be considered together.
Window Wizard
Crafting Views. Enhancing Spaces.
The Window Wizard Approach
At Window Wizard Building Solutions LLP, we believe that every opening should be designed around the architecture and the people who will use the space.
Our approach begins with understanding the project: the building type, opening dimensions, design intent, functionality, finishes and site conditions.
We work with homeowners, architects, builders, developers and consultants across residential, hospitality, healthcare and commercial applications.
From premium aluminium windows and doors to curtain walls and façade systems, our focus remains on three things:
The right solution. Precise execution. A finish that belongs to the architecture.
As a channel partner of AluK, Window Wizard brings together advanced aluminium system solutions with careful project planning, fabrication, installation and on-site coordination.
Whether the requirement is for a contemporary builder floor in Gurgaon, a luxury residence in Delhi NCR, a farmhouse, hospital or corporate façade, the objective is not simply to fill an opening. It is to create a solution that improves how the building looks, feels and functions.
Final Thoughts
Windows, doors and façades are among the most visible and frequently used elements of any building.
They shape the view from inside, the appearance from outside and the relationship between architecture, light and everyday life.
The right aluminium solution cannot be chosen by appearance alone. It must respond to the building type, opening size, glass requirement, expected usage and site conditions. Equally, it must be fabricated and installed with the precision needed to translate a design into a dependable finished result.
When all these elements come together, windows and façades stop feeling like separate products. They become an integral part of the architecture.
Planning Aluminium Windows, Doors or a Façade System?
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Frequently Asked Questions
Are aluminium windows suitable for premium homes?
Yes. Aluminium supports clean profiles, large glazed openings, multiple configurations and a wide range of finishes, making it suitable for builder floors, villas, farmhouses and premium residences. The correct system should be selected according to the opening dimensions and intended use.
Which is better: sliding or casement windows?
Neither is universally better. Sliding windows are useful where space efficiency and wider glazing are priorities. Casement windows may be preferred where controlled ventilation and hinged operation are required. Many homes use a combination of both.
What is the difference between a window system and ordinary aluminium fabrication?
A system-based solution uses coordinated profiles, accessories, hardware and fabrication details designed to work together. The actual outcome still depends on appropriate system selection, fabrication and installation.
Can aluminium doors be used for large farmhouse openings?
Yes, subject to the opening dimensions, system capability, glass selection, hardware and structural requirements. Large-format openings should be assessed and planned carefully rather than treated like standard doors.
What is a curtain wall façade?
A curtain wall is a non-load-bearing external system commonly used to create glazed façades on offices, hospitals, hotels and commercial buildings. It forms part of the building envelope but does not carry the primary structural load of the building.
When should a window or façade specialist join a project?
Ideally, the specialist should be involved during the design or early construction stage. Early coordination can help finalise opening sizes, system configurations, interfaces and installation requirements before civil finishes are completed.