Glass selection in curtain wall facades should not be based solely on color or exterior appearance. Glass directly affects the building’s thermal insulation, solar control, daylight utilization, indoor comfort, safety, acoustic performance, and architectural character.

Even within the same curtain wall system, different glass performances may be required depending on building orientation, function, glass dimensions, building height, wind loads, and architectural expectations.

Especially in offices, plazas, hotels, hospitals, showrooms, factory administration buildings, and commercial buildings with large glazed areas, incorrect glass selection may cause:

excessive solar heat gain,
high cooling loads,
glare,
insufficient daylight,
unwanted external reflection,
insufficient thermal insulation,
thermal breakage risk,
visible color differences between vision and spandrel zones.

For this reason, curtain wall glass selection should be evaluated together with the glass, aluminum supporting system, insulation, spandrel zone, drainage, anchoring, and fire safety details.

For the different systems applied by Optimal Mimarlık, see Curtain Wall Systems.

Why Is Glass Selection Important in Curtain Wall Facades?

A curtain wall is not merely a decorative building surface made of glass and aluminum. It is a technical building envelope that manages the relationship between the interior and exterior environment.

The following criteria should be evaluated together when selecting facade glass:

building function,
facade orientation,
solar exposure conditions,
daylight requirements,
solar control,
thermal insulation,
glass dimensions,
wind loads,
safety requirements,
acoustic performance,
external reflectance,
glass color,
visual consistency between vision and spandrel zones,
curtain wall system type.

Therefore, the first question should not simply be “Which glass color should be used?” but rather “What technical performance is expected from the facade?”

For the general criteria affecting system selection, see Curtain Wall Selection Guide.

What Is Vision Glass?

Vision glass is the transparent or semi-transparent section of a curtain wall that provides occupants with a view to the exterior.

Vision glass is commonly used in:

offices,
hotels,
showrooms,
lobbies,
retail stores,
hospitals,
educational buildings,
factory administration buildings.

A properly selected vision glass:

provides sufficient daylight,
limits excessive solar heat gain,
reduces heat losses,
provides acoustic performance where required,
creates an appearance compatible with the architectural design.

For this reason, visible light transmittance, solar factor, Ug value, external reflectance, internal reflectance, glass color, and safety characteristics should be assessed together.

What Is Spandrel Glass?

Spandrel glass is the glazed section of a curtain wall used to conceal floor slabs and opaque construction components located in front of the slab edge.

Depending on the project, the spandrel zone may include:

under-screed metal sheet,
fire-stop barrier,
stone wool providing sound insulation,
opacifying coating,
ceramic enamel or frit layer,
slab-edge closure and detailing.

The optical environment behind spandrel glass is therefore different from the interior space behind vision glass.

As a result, even when the same or a similar outer glass is used, vision glass and spandrel glass do not always appear identical from the exterior.

Why Do Vision Glass and Spandrel Glass Appear Different in Color?

One of the key architectural considerations in curtain wall design is achieving controlled visual consistency between vision and spandrel zones.

The perceived difference in color is determined by:

glass coating type,
external reflectance,
visible light transmittance,
base glass color,
coating surface position,
color of the backing layer in the spandrel zone,
ceramic enamel or frit color,
interior brightness or darkness,
angle of sunlight,
facade orientation,
reflections of the sky and surrounding buildings.

Reflective glass reduces the visibility of construction components located behind the spandrel zone.

On large projects, final color decisions should not be based solely on small glass samples. A full-scale mock-up should be evaluated whenever visual continuity is critical.

What Is Low-E Glass?

Low-E (Low Emissivity) glass is performance glass with a special coating that reduces long-wave radiant heat transfer.

Low-E glass improves thermal insulation performance.

However, Low-E glass and solar control glass are not the same.

A glass product may significantly reduce winter heat loss but may not provide the required solar control during summer conditions.

For this reason, thermal insulation and solar control should be considered together on extensively glazed buildings.

For current Low-E and Solar Low-E products, see the Şişecam Flat Glass Product Catalogue.

What Is Solar Control Glass?

Solar control glass limits the amount of solar energy entering the interior.

Solar control becomes particularly important on large glazed surfaces facing south, southwest, and west.

Excessive solar heat gain:

increases indoor temperatures,
increases cooling loads,
reduces occupant comfort,
causes glare on screens and work surfaces.

However, reducing light transmittance excessively in order to increase solar control is also undesirable.

The objective is not to select the darkest or most reflective glass available, but to establish the right balance between daylight, solar control, energy performance, and architectural appearance.

Şişecam Tentesol and Tinted Glass

Şişecam Tentesol is a family of reflective solar control glass. Its pyrolytic hard coating, applied during production to clear or tinted float glass, provides both solar control and a reflective exterior appearance.

This product family is used in curtain wall facades and insulating glass units. Depending on the project, tempering, heat strengthening, ceramic enameling, or laminating processes are also applied.

The glass products used in different Optimal Mimarlık projects demonstrate how the same 6+20+6 mm insulating glass configuration creates very different architectural appearances when different outer glass types are selected.

Maslak Plaza – Tentesol Blue

At Maslak Plaza, 6+20+6 mm Tentesol Blue glass was used.

Tentesol Blue combines a reflective appearance with solar control. Its blue-toned exterior appearance gives the glazed facade a stronger architectural identity.

Şişecam Tentesol Blue

Optimal Mimarlık – Maslak Plaza

Miletiket Factory – Tinted Grey

At Miletiket Factory, 6+20+6 mm Tinted Grey glass was used.

Tinted glass is colored float glass produced by adding coloring agents to the glass composition during manufacturing. In Şişecam’s current product range, the corresponding product is Şişecam Tinted Float Glass – Grey.

Grey tinted glass creates a darker, more neutral facade appearance and provides solar and light control.

Şişecam Tinted Float Glass

Optimal Mimarlık – Miletiket Factory

Gülsoy Mercedes Florya – Tentesol Silver

At Gülsoy Mercedes Florya, 6+20+6 mm Tentesol Silver glass was used.

Tentesol Silver creates a strong, homogeneous exterior appearance through its neutral silver tone and highly reflective character, particularly on showrooms, offices, and commercial facades.

Its reflective surface also reduces the visibility of slab-edge components in spandrel zones.

Şişecam Tentesol Silver

Optimal Mimarlık – Gülsoy Mercedes Florya

Although the same 6+20+6 mm basic configuration was used in all three applications, the blue, grey, and silver characteristics of the outer glass demonstrate that glass thickness alone does not define facade performance or architectural appearance.

What Does 6+20+6 mm Glass Mean?

In facade projects, 6+20+6 mm generally describes the following insulating glass configuration:

6 mm outer glass + 20 mm cavity + 6 mm inner glass

However, writing only “6+20+6” does not fully define the performance of the insulating glass unit.

The following should also be specified:

outer glass product type,
outer glass coating,
whether the inner glass is clear or Low-E,
whether the glass panes are tempered,
whether lamination is used,
whether the cavity contains air or gas,
spacer type,
coating surface position.

For this reason, two insulating glass units with the same 6+20+6 geometry may have very different Ug values, light transmittance, solar factor, and reflectance.

What Does Solar Low-E Glass Provide?

Solar Low-E glass combines solar control and low-emissivity thermal insulation in the same product structure.

Modern curtain wall facades are not limited to reflective solar control glass. Solar Low-E products are also used when a more neutral appearance, higher daylight transmission, or a lower Ug value is required.

Şişecam’s current range includes Solar Low-E product families such as Duosol and Ecosol.

Glass selection should therefore be based not only on color or product name, but also on technical data such as light transmittance, solar factor, Ug value, and reflectance.

Şişecam Flat Glass Product Catalogue

Which Technical Values Should Be Considered When Selecting Curtain Wall Glass?

Visible Light Transmittance

Visible light transmittance indicates how much visible light passes through the glass into the interior.

Higher light transmittance provides more daylight. However, high light transmittance alone does not indicate good facade performance.

Solar Factor – g-Value

The solar factor (g-value) indicates the proportion of total solar energy reaching the interior through the glass.

A lower g-value indicates stronger solar control.

TS EN 410 is one of the primary reference standards used to determine the luminous and solar characteristics of glazing.

Ug Value

Ug represents the thermal transmittance of the glass or insulating glass unit.

A lower Ug value indicates better thermal insulation.

EN 673 is one of the principal standards used to calculate the Ug value of glass.

Ug and Ucw Are Not the Same

Ug: thermal transmittance of the glazing unit.

Ucw: thermal transmittance of the entire curtain wall system, including glass, aluminum framing, glass edge zones, spandrel areas, and other system components.

Therefore, using glass with a low Ug value does not mean the entire facade has the same U-value.

EN 13830 – Curtain Walling is one of the primary reference standards for the overall performance assessment of curtain wall systems.

What Is Glass Selectivity?

In facade glass, selectivity describes the relationship between daylight transmission and solar energy control.

Particularly in offices and commercial buildings with large glazed areas, the combination of high visible light transmittance and a low solar factor provides a significant performance advantage.

For this reason, solar control should not be evaluated simply by looking at how dark the glass appears.

How Should Glass Color Be Selected?

Silver, blue, grey, bronze, neutral grey, and other glass colors are important elements of architectural design.

However, glass does not appear exactly the same on a building as it does in a small sample.

The perceived glass color changes depending on:

the sky,
facade orientation,
solar angle,
surrounding buildings,
interior brightness,
coating surface position,
layers behind the spandrel zone.

For this reason, on projects where visual consistency between vision and spandrel glass is important, large-format samples or full-scale mock-ups should be evaluated.

When Should Tempered Glass Be Used?

The decision to temper glass depends on:

glass dimensions,
wind loads,
solar energy absorption,
shading conditions,
support conditions,
safety requirements,
thermal stresses.

In solar control glass, high solar energy absorption increases the risk of thermal breakage when the glass configuration is not properly designed.

The TS EN 12150 series is one of the main standards covering thermally toughened soda-lime silicate safety glass.

When Should Laminated Glass Be Used?

Laminated glass is a safety glass made by bonding two or more glass panes with interlayers.

When breakage occurs, the glass fragments remain attached to the interlayer.

For this reason, laminated glass or tempered-laminated glass combinations are used in:

areas with fall risk,
spandrels,
glass balustrades,
entrance canopies,
skylight systems,
glass roofs,
facade areas requiring enhanced safety.

TS EN 14449 is among the relevant standards for laminated glass products, while TS EN 12600 addresses impact behavior and classification.

Standards for Insulating Glass Units

The performance of double- and triple-glazed insulating glass units depends on more than the properties of the individual glass panes.

The following components also affect performance:

cavity width,
spacer system,
gas fill,
primary seal,
secondary seal,
edge construction.

The EN 1279 / TS EN 1279 standard series is one of the principal references for insulating glass units.

For coated glass products, the TS EN 1096 – Glass in Building – Coated Glass series is also important.

Technical data provided in product data sheets should be assessed together with these standards.

Should the Same Glass Be Used on Every Facade Orientation?

The same glass is not required on every project orientation.

North-, south-, east-, and west-facing facades are exposed to different solar conditions.

For example, west-facing facades are exposed to significant afternoon solar loads during summer, while the solar control requirement on a north facade is different.

For this reason, different performance glass may be used on different orientations in large projects.

However, differences in:

color,
external reflectance,
visible light transmittance

should not create unwanted visual inconsistency across the facade.

Technical performance and architectural continuity should therefore be evaluated together.

How Is Curtain Wall Glass Thickness Determined?

Glass thickness should not be selected based on standard practice alone.

The following parameters should be evaluated together:

glass width,
glass height,
wind load,
support conditions,
glass type,
tempering,
lamination,
insulating glass configuration,
allowable deflection,
safety requirements.

For this reason, the general assumption that “6 mm glass is always used in curtain walls” is technically incorrect.

For the effect of wind loads and other design criteria on facade systems, see Common Mistakes in Curtain Wall Systems.

Glass Selection in Capped, Semi-Capped and Structural Silicone Curtain Walls

Although the core glass performance criteria remain the same, the way the glass is connected to the curtain wall system changes.

Capped Curtain Wall

Glass panes are mechanically retained by external pressure plates and cover caps.

Semi-Capped Curtain Wall

A mechanical cap is used in one direction and a silicone joint in the other, creating different architectural expressions.

At Miletiket Factory, 6+20+6 mm Tinted Grey glass was used in combination with a semi-capped curtain wall system.

Structural Silicone Curtain Wall

The continuous appearance of exterior aluminum caps is reduced, creating a more glass-dominant and visually uninterrupted facade.

At Maslak Plaza, 6+20+6 mm Tentesol Blue was used, while at Gülsoy Mercedes Florya, 6+20+6 mm Tentesol Silver was applied with structural silicone curtain wall systems.

For technical details, see Capped, Semi-Capped and Structural Silicone Curtain Wall Systems.

For high-rise buildings or projects where modular fabrication provides advantages, Unitized Glass Curtain Wall Systems are also used.

Comparing Glass Performance with Şişecam GlassTool

Manufacturer technical data should be used when evaluating glass combinations.

Şişecam’s GlassTool allows different glass combinations to be compared based on:

light transmittance,
solar factor,
U-value,
performance of different glass and coating combinations.

Şişecam GlassTool

Such calculation tools are useful during preliminary selection. Final product selection should be made by evaluating the project specification, facade system, structural requirements, and manufacturer technical data together.

How Should the Correct Curtain Wall Glass Be Selected?

There is no single “best curtain wall glass.”

The correct glass is the glass that meets the project’s architectural and technical requirements together.

The selection process generally follows these stages:

Determine the building function.
Analyze facade orientations and solar exposure.
Define thermal and solar control targets.
Evaluate daylight requirements.
Determine architectural color and reflectance.
Define safety requirements.
Evaluate acoustic requirements.
Design vision and spandrel zones together.
Perform structural checks based on glass dimensions and wind loads.
Check compatibility between the glass and curtain wall system.
Prepare a mock-up where required.
Verify the final glass configuration against manufacturer technical data, relevant standards, and the project specification.

Optimal Mimarlık Curtain Wall Solutions

Optimal Mimarlık considers glass selection not as an isolated material choice, but as a part of the complete curtain wall system design.

A properly designed system is created by coordinating:

glass + aluminum supporting system + anchoring + insulation + spandrel + drainage + fire safety + installation details

as an integrated whole.

In capped, semi-capped, structural silicone, and unitized curtain wall systems, selecting glass according to:

wind loads,
solar and thermal performance,
architectural design,
building use,
facade orientation,
safety criteria,
maintenance conditions

provides durable and controlled facade performance.

For Optimal Mimarlık’s approach to system selection, design, fabrication, and installation, see Curtain Wall Services.

Quick Answers

What is vision glass?

Vision glass is the glazed curtain wall zone through which occupants can see from the interior to the exterior.

What is spandrel glass?

Spandrel glass is the glazed area used to conceal floor slabs and opaque construction components located at the slab edge.

What is Tentesol glass?

Tentesol is Şişecam’s reflective solar control glass family. It is available in blue, silver, and other color/coating options.

Are Low-E glass and solar control glass the same?

No. Low-E glass reduces heat loss. Solar control glass limits solar energy entering the interior. Solar Low-E products combine both functions.

What does 6+20+6 glass mean?

It generally refers to an insulating glass configuration consisting of 6 mm outer glass + 20 mm cavity + 6 mm inner glass. It does not, by itself, define coating, tempering, lamination, or Low-E properties.

What is the difference between Ug and Ucw?

Ug refers only to the thermal transmittance of the glazing unit. Ucw refers to the thermal transmittance of the entire curtain wall, including glazing, framing, and other components.

Do vision and spandrel glass appear exactly the same in color?

Not always. Under-screed metal sheets, fire-stop barriers, stone wool, opacifying layers, and other slab-edge details behind the spandrel zone change the optical background. Glass reflectance and exterior lighting conditions also affect perceived color.

How is curtain wall glass thickness determined?

Glass thickness is determined by evaluating glass dimensions, wind loads, support conditions, glass type, tempering, lamination, safety requirements, and allowable deflection together.

Technical Editor and Content Review:
Mehmet Beşe Polatkan, Architect (YTU)

Copyright and Use

This content belongs to Optimal Mimarlık Yapı ve Tic. A.Ş. and is protected under Law No. 5846 on Intellectual and Artistic Works of the Republic of Türkiye.

It may not be copied, reproduced, or republished without permission. For quotations made within the scope of Article 35 of Law No. 5846, the source must be cited as Optimal Mimarlık – www.optimalmimarlik.com.