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Curtain Wall vs Window Wall: What Is the Real Difference?

The most important difference in curtain wall vs window wall is not the glass. It is the load path and how the façade relates to the building structure.

A curtain wall is generally designe d as a continuous, non-load-bearing façade system supported by the primary structure through anchors. It can extend across multiple storeys and is engineered as a building-envelope system.

A window wall is installed within the floor-to-floor opening at each level. Each unit or group of units is supported by the slab or surrounding structure at that floor rather than forming one continuous mullion grid across multiple storeys.

That difference affects:

• Structural design
• Mullion geometry
• Anchoring
• Installation sequence
• Façade drainage
• Cost
• Maintenance
• Suitable building types

In Singapore, the current SS 654:2020+A1:2023 Code of Practice for Curtain Walls covers metal-framed curtain walls and includes requirements for air permeability, watertightness and structural performance, as well as brackets, anchors, flashings, gutters and other associated components. It replaced CP 96:2002.

Key principle: choose the façade system according to the building’s load path and envelope requirements—not simply the appearance of the elevation.

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Quick Comparison

Neither system is automatically the cheaper choice for every project. The final cost depends on span, glazing, anchors, thermal requirements, access, installation sequence and façade geometry.

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1. The Load Path Comes First

Every façade must answer the same question:

How are the dead load and wind load transferred from the façade to the building structure?

A curtain wall normally uses a continuous grid of mullions and transoms connected to the structure through engineered anchors.

The load path is broadly:

glass → framing → anchors → slab / structure

A window wall uses a different arrangement:

window assembly → local support / slab edge → structure

Because each floor can receive its own window units, window wall can simplify the structural organization of buildings with repeated floor-to-floor openings.

This is why the visual similarity between the two systems can be misleading.

Two buildings may both appear to have a continuous glass façade while using very different structural systems behind the glazing.

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2. Curtain Wall: When the Façade Needs to Act as One System

A curtain wall is designed as a coordinated building-envelope system rather than a collection of independent windows.

Typical components include:

• Aluminum mullions
• Transoms
• Pressure plates or glazing beads
• Gaskets
• Spandrel zones
• Anchors
• Flashings
• Drainage components

The curtain wall may be:

stick-built — assembled on site from individual profiles and components

or:

unitized — factory-assembled into larger panels and installed as prefabricated units.

Our guide to unitized vs stick-built curtain wall systems explains how the installation strategy changes procurement, factory assembly and site work.

Curtain wall is particularly relevant where a project requires:

• Continuous multi-storey glazing
• Large repetitive elevations
• Defined façade drainage
• Engineered slab-edge anchors
• Coordinated spandrel and vision areas

For Singapore projects, SS 654 is the relevant current curtain-wall code framework.

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3. Window Wall: The Floor-by-Floor Alternative

A window wall places the glazing within each floor-to-floor opening.

Instead of one continuous structural grid extending through several storeys, the façade is interrupted by the slab structure at each level.

This can make window wall attractive for:

• Residential towers
• Condominiums
• Repeated punched openings
• Mid-rise buildings
• Projects where installation is organized floor by floor

Its main procurement advantage is often repeatability.

Each level can use a similar opening schedule, with units fabricated and installed according to that floor’s dimensions.

However, window wall should not simply be selected because it is “cheaper.”

The project still needs to resolve:

• Water management
• Perimeter sealing
• Slab-edge conditions
• Thermal bridges
• Anchoring
• Fire and smoke separation where applicable
• Acoustic requirements

The façade strategy must work as a complete wall assembly.

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Curtain Wall vs Window Wall: Structural Decision Table

The word “may” matters. System selection should follow the project drawings, structural calculations and façade consultant’s requirements.

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4. Cost: Why Curtain Wall Is Usually More Complex

Curtain wall generally requires more continuous façade infrastructure.

The cost can increase because of:

• Mullion and transom depth
• Anchoring systems
• Pressure plates and covers
• More complex drainage
• Spandrel treatment
• Engineering
• Access equipment
• Site installation
• Factory assembly for unitized systems

Window wall can reduce some of those costs by treating each floor as a series of individual openings.

But the comparison should never be reduced to:

Curtain wall = expensive
Window wall = cheap

A high-rise window wall still requires substantial engineering, perimeter sealing, fire and acoustic coordination, and slab-edge detailing.

The right comparison is the complete installed façade system.

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5. Installation and Project Schedule

Installation strategy is another major difference.

Curtain Wall

Stick-built systems are assembled progressively at the façade.

Unitized systems arrive as larger factory-assembled panels.

The project therefore depends heavily on:

• Anchor accuracy
• Panel logistics
• Crane or hoist access
• Floor sequencing
• Tolerances
• Weather conditions

Window Wall

Window wall is generally installed more directly within each floor opening.

That can work well where:

• Floor layouts repeat
• Openings are standardized
• Installation follows the building floor sequence
• Window units can be delivered in manageable batches

For a high-volume residential project, this floor-by-floor approach can provide a straightforward relationship between the window schedule and installation schedule.

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6. Thermal and Weather Performance

Singapore’s climate makes façade performance particularly important.

BCA Green Mark 2021 is Singapore’s current green-building certification framework and is specifically tailored to the tropical climate. The current second edition applies to projects assessed from 1 June 2024 onward.

BCA’s energy-modelling guidance also identifies SS 212:2007 for aluminum alloy windows and SS 654 for curtain walls, and states that windows and curtain walls are to be designed so that air leakage does not exceed the applicable limits.

For either façade system, therefore, evaluate:

The correct thermal comparison is not simply:

curtain wall vs window wall

but:

complete façade build-up vs complete façade build-up.

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7. When Does a Window Wall Become the Wrong Choice?

Window wall becomes less attractive when the façade needs to behave as a continuous engineered skin.

Potential warning signs include:

• Large continuous spans
• Complex façade geometry
• Significant movement between floors
• Highly exposed elevations
• Extensive curtain-wall-like glazing
• Complex integrated drainage
• Extensive façade maintenance access requirements

Similarly, curtain wall can be excessive for a building that primarily consists of repeated floor-to-floor openings.

The strongest specification is therefore the one that solves the actual building problem without adding unnecessary structural or installation complexity.

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A Practical Procurement Framework

Before requesting quotations, define the façade requirements in one technical schedule.

This is more useful than asking a supplier simply:

“How much is curtain wall per square metre?”

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How to Compare Curtain Wall and Window Wall Quotes

Put both systems into the same procurement sheet.

A lower price is not necessarily a better quotation if the supplier has excluded structural calculations, premium glazing, drainage components or installation engineering.

For an accurate commercial quotation, use Starveil’s aluminum window and façade drawing submission guide.

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Singapore Facade Decision Guide

The correct design may also combine systems.

For example, a project can use:

curtain wall at the tower façade + window wall in residential zones + storefront at the podium.

That is often more efficient than forcing one system across the entire building.

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Frequently Asked Questions

What is the difference between a curtain wall and a window wall?

The main difference is the load path. A curtain wall is generally a continuous façade system supported by the primary structure through anchors, while window wall is installed within each floor-to-floor opening and supported at each level.

Which is cheaper, curtain wall or window wall?

Window wall is often less expensive for buildings with repetitive floor-to-floor openings because the system can be simpler and installed level by level. Curtain wall usually requires more continuous framing, anchoring and façade engineering. The actual cost depends on the complete project specification.

Can window wall be used on a high-rise?

Yes, depending on the building design and applicable requirements. It is common in some residential high-rise applications with repetitive floor-to-floor openings. The decision must account for structural loads, movement, weather performance, fire separation, acoustics and installation conditions.

What is a unitized curtain wall?

A unitized curtain wall is a façade system assembled into larger factory-built panels before delivery to the site. It can reduce site assembly and support rapid floor-by-floor installation on repetitive high-rise façades.

What is stick-built curtain wall?

Stick-built curtain wall is assembled on site from individual mullions, transoms, glazing components and related hardware. It offers flexibility for varying façade geometry but generally requires more site assembly than a unitized system.

What standard applies to curtain walls in Singapore?

The current Singapore standard is SS 654:2020+A1:2023, which covers metal-framed curtain walls, including design and installation and performance relating to air permeability, watertightness and structural performance.

Can curtain wall and window wall be used on the same building?

Yes. A mixed façade strategy can use curtain wall, window wall and storefront in different zones according to building height, geometry, structural requirements and architectural intent.

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Bottom Line

The curtain wall vs window wall decision should start with the load path, not the façade rendering.

Use curtain wall when the building needs a continuous, engineered façade skin spanning multiple storeys.

Use window wall when repeated floor-to-floor openings can be supported independently at each level.

For Singapore projects, also evaluate air, water, thermal performance, structural movement, installation sequence and the applicable SS 654/BCA requirements. BCA’s Green Mark 2021 framework and current energy-modelling guidance reinforce the need to consider the building envelope as a complete performance system rather than an isolated window product.

The most efficient project may not use one façade system everywhere.

Curtain wall + window wall + storefront can often be combined to match the actual building zones.

Request a Facade System Recommendation

Send Starveil your:

• Number of floors
• Building height
• Elevation drawings
• Opening schedule
• Project location
• Design wind information
• Glazing requirements

Our engineering team can compare the curtain wall vs window wall options, review the load path and prepare the appropriate system recommendation and quotation.

Request a Facade System Review →