Structural silicone, capped and semi-capped curtain wall systems are widely used in offices, plazas, hotels, residential buildings, showrooms, hospitals, educational facilities, factory administration buildings and commercial projects.
Although glass and aluminium define the architectural appearance of these systems, the performance and service life of a curtain wall are not determined solely by the quality of the glass or aluminium profiles.
A curtain wall is an integrated building-envelope system consisting of:
glass + aluminium mullions and transoms + anchors + connection components + gaskets + sealants + pressure plates + drainage system + insulation + fire-stopping details + installation tolerances.
In a capped curtain wall, glass units are supported on aluminium framing and mechanically retained by pressure plates and external caps. In a structural silicone curtain wall, visible external caps are eliminated or reduced to create a more continuous glazed surface.
The basic characteristics and application principles of these systems are explained in Capped, Semi-Capped and Structural Silicone Curtain Wall Systems.
The correct facade solution therefore begins not simply with selecting glass and aluminium profiles, but with understanding how the glazing, supporting structure, wind and seismic actions, connections, drainage, thermal and acoustic performance, fire safety and installation details will work together.
1. Treating a Curtain Wall as Simply Glass and Aluminium Cladding
One of the most fundamental mistakes is treating a curtain wall as a decorative glazed surface attached to the outside of a building.
A curtain wall is a non-load-bearing building-envelope system. It must transfer its own weight and environmental actions, including wind pressure and suction, through its connections to the primary building structure.
The facade therefore requires a continuous and calculated load path:
glass → glazing supports and fixings → mullions and transoms → brackets and anchors → primary structure.
The different systems used to create this building envelope are described in Curtain Wall Systems.
A successful facade must be considered as a complete engineered system rather than a collection of individual products.
2. Selecting Aluminium Profiles Without Structural Calculations
Using an aluminium profile simply because it performed successfully on another project is not a sufficient basis for profile selection.
Profile sections are influenced by:
- building height,
- project location,
- facade orientation,
- facade geometry,
- mullion spacing,
- floor-to-floor height,
- glass module dimensions,
- support conditions,
- wind pressure and suction,
- allowable deflection criteria.
A profile suitable for one facade geometry may not be suitable for another.
In Türkiye, structural loading must be evaluated according to the regulations, standards and project requirements applicable to the building. TS 498 – Design Loads for Buildings is among the references used in determining building loads.
However, determining the design load does not itself determine the aluminium profile. The resulting actions must be evaluated according to the actual facade geometry, spans, support conditions and structural system.
For project-specific design and implementation processes, see Curtain Wall Services.
The correct profile is not the heaviest profile. It is the calculated profile that satisfies the required strength and deformation criteria for the project.
3. Selecting Glass Thickness by Habit
“We used this glass composition on another project” is not a substitute for glass design.
Glass selection must consider:
- panel width and height,
- wind actions,
- support conditions,
- heat treatment,
- laminated glass requirements,
- insulating glass configuration,
- safety requirements,
- solar control,
- Low-E performance,
- acoustic requirements.
As glass dimensions increase, its behaviour under wind loading changes.
Therefore:
glass dimensions + glass composition + support conditions + facade structure
must be evaluated together.
Large glass dimensions may also affect transportation, lifting, installation methods and replacement procedures. These considerations should be addressed before the facade module is finalised.
4. Treating Structural Silicone as Ordinary Weather Sealant
This is one of the most critical mistakes in structural silicone glazing.
Structural silicone is not simply a sealant used to fill a joint.
In a Structural Sealant Glazing (SSG) system, structural silicone forms part of the engineered connection between the glazing and its supporting frame.
The European Organisation for Technical Assessment provides technical assessment documents covering bonded glazing kits and bonding sealants.
EOTA – European Assessment Documents
Structural glazing technical guidance from Dow also addresses project review, substrate compatibility, joint design, application procedures, quality control and documentation.
Structural silicone is not merely a gap-filling material. It is part of an engineered facade connection.
5. Determining Structural Silicone Joint Dimensions Without Calculation
Using the same structural silicone joint dimensions on every project is incorrect.
The required joint geometry depends on factors including:
- glass dimensions,
- design wind load,
- facade geometry,
- silicone design properties,
- expected movement,
- supporting frame configuration.
Structural bite and joint geometry must therefore be established specifically for the project and the selected system.
There is no single universal structural silicone joint dimension that is correct for every facade.
6. Failing to Verify the Bonding Surfaces
Selecting the correct structural silicone does not guarantee a correct structural glazing connection.
The actual substrates must also be evaluated. These can include glass, coated or fritted glass surfaces, anodised aluminium, painted aluminium and other materials that come into contact with the silicone.
Oil, dust, moisture, manufacturing residues or unsuitable cleaning products compromise surface preparation and adhesion.
Cleaning, priming and application procedures must follow the requirements established for the selected silicone and substrates.
Structural silicone adhesion is not assumed; it is verified through the required project and quality-control procedures.
7. Ignoring Compatibility Between Silicone and Other Facade Components
Structural silicone can interact with more materials than simply glass and aluminium.
These can include:
- spacers,
- gaskets,
- setting materials,
- insulating-glass edge seals,
- backing materials,
- other sealants.
Material incompatibility can adversely affect adhesion or long-term silicone performance.
The materials in contact with one another must therefore be checked for compatibility before production begins.
8. Moving or Installing Glazed Frames Before Adequate Silicone Cure
Structural silicone requires adequate curing before glazed frames or cassettes are subjected to loads that the connection is not yet ready to resist.
Curing depends on factors such as:
- silicone type,
- joint geometry,
- temperature,
- relative humidity,
- manufacturer's requirements.
Production and installation schedules must therefore be coordinated with the specified curing and quality-control procedures.
The required curing process cannot be shortened simply to accelerate the construction programme.
9. Incorrectly Transferring the Dead Load of the Glass
The self-weight of the glass and the transfer of wind loads are different engineering issues.
Depending on the structural glazing system, the glass dead load must be transferred through the support arrangement defined in the approved facade design.
Setting blocks, mechanical supports and cassette geometry are therefore not secondary accessories.
Incorrect support causes:
- excessive edge stresses,
- deformation of insulating glass units,
- unintended loading of structural silicone,
- displacement of glazing units.
The load-transfer mechanism must be clearly defined in the project details.
10. Incorrect Installation of Pressure Plates in Capped Curtain Walls
Pressure plates are critical components of mechanically retained capped curtain wall systems.
Incorrect fastener type, spacing or tightening causes:
- uneven gasket compression,
- incorrect glass seating,
- reduced air and water performance,
- visual irregularities in the facade.
The fastening method must follow the technical requirements of the selected curtain wall system.
Tighter does not automatically mean more watertight.
11. Stretching EPDM Gaskets During Installation
EPDM gaskets are relatively small components with a major influence on facade performance.
If a gasket is stretched during installation, it tends to recover towards its original length over time. This creates gaps, particularly at joints and corners.
These openings cause air and water leakage.
Gaskets must therefore be installed without uncontrolled stretching, and their joints and corners must be completed according to the system requirements.
12. Blocking Drainage Channels and Weep Paths
Curtain walls should not be designed on the assumption that absolutely no water will ever reach the internal drainage zones of the system.
Water reaching these zones must be collected and discharged safely.
Drainage paths can be blocked by:
- excess silicone,
- incorrectly positioned gaskets,
- manufacturing debris,
- installation residues.
Blocked drainage results in water accumulation, moisture, corrosion, wet insulation and interior leakage.
A correctly designed curtain wall does not merely resist water; it manages and drains the water that reaches its controlled drainage zones.
13. Incorrect Mullion-to-Transom Connections
Connections between vertical mullions and horizontal transoms are not merely mechanical junctions.
They are also part of the water-management strategy of many curtain wall systems.
Incorrect sealing or unapproved modification of these junctions disrupts the intended drainage path.
Filling every visible cavity with sealant on site is not good facade practice.
The drainage principle of the selected curtain wall system must be preserved.
14. Relying Only on External Silicone at Perimeter Joints
Curtain wall interfaces with reinforced concrete, masonry, parapets, roofs, entrance canopies, aluminium windows and other facade claddings cannot be resolved simply by applying a bead of silicone to the external surface.
These interfaces must coordinate:
air tightness + water management + thermal insulation + movement accommodation + drainage.
The perimeter detail must therefore be designed as part of the complete building envelope.
15. Transferring Structural Construction Tolerances Directly to the Facade
The primary structure is not built with zero tolerance.
Slab edges, columns and other structural elements deviate from their theoretical positions within construction tolerances.
The facade bracket and anchoring system must accommodate these differences.
Otherwise, the result is:
- incorrect vertical alignment,
- irregular glass joints,
- misaligned caps,
- steps between facade modules.
Correct curtain wall installation starts with site measurement and establishment of reference axes.
16. Selecting Anchors Without Engineering Calculations
Anchors form a critical part of the load path between the facade and the primary structure.
Anchor design must consider:
- bracket reactions,
- connection geometry,
- substrate properties,
- edge distances,
- anchor resistance,
- adjustment requirements,
- installation tolerances.
The connection cannot be selected solely according to installer preference or previous projects.
A safe curtain-wall load path starts at the facade and ends at a verified connection to the primary structure.
17. Ignoring Thermal Expansion and Fixed/Sliding Connection Principles
Aluminium expands and contracts as temperature changes.
If long mullions are restrained incorrectly, additional stresses develop in the profiles and their connections.
Profile joints, fixed points and sliding connections must therefore follow the engineering principles of the selected system.
Completely locking the facade does not make it safer.
A correctly engineered facade carries the required loads while allowing calculated movements to occur.
18. Ignoring Seismic Movement and Inter-Storey Drift
A curtain wall is not the primary structural frame.
When the reinforced-concrete or steel structure moves during an earthquake, the facade must accommodate the relevant project movements without uncontrolled contact or damage.
Failure to consider inter-storey movement causes:
- glass edge contact,
- profile deformation,
- excessive movement in silicone joints,
- gasket separation,
- overstressed connections.
The curtain wall must therefore be coordinated with the structural movement criteria established for the building.
19. Treating the Insulating Glass Edge Seal Independently from Structural Glazing
In a structural silicone facade, it is not sufficient to consider only the visible structural silicone connection.
The edge-seal system of the insulating glass unit must also be compatible with the structural glazing application.
The requirements of the glass manufacturer, insulating-glass manufacturer, structural silicone manufacturer and curtain wall system must be coordinated.
Facade glazing is not simply a pane of glass. It is an engineered component of the complete facade system.
20. Selecting Vision and Spandrel Glass Independently
Vision glass and spandrel glass are perceived together on the completed elevation.
Colour, reflection and visual uniformity can be affected by:
- glass coating,
- frit or opacifier,
- insulation behind the spandrel,
- shadow-box configuration,
- internal backing surfaces,
- external lighting conditions.
Vision and spandrel areas should therefore be assessed together.
For significant projects, full-scale samples or mock-ups provide a more reliable basis for evaluating the final facade appearance.
21. Inadequate Perimeter Fire-Stopping at Floor Slabs
The junction between a curtain wall and a floor slab is a critical fire and smoke-control zone because the facade continues vertically past the slab edge.
The gap between the slab and facade must be addressed in accordance with the project's fire strategy, applicable regulations and tested system requirements.
In Türkiye, the Regulation on Fire Protection of Buildings is one of the principal regulatory references, together with the standards and approved systems applicable to the project.
Simply placing mineral wool into the slab-edge void does not by itself define a complete fire-stopping system.
The solution must consider:
materials + dimensions + fixing + continuity + smoke control + facade geometry.
22. Ignoring Thermal Bridges
Curtain-wall energy performance is not determined solely by the Ug value of the glazing.
Overall performance is also influenced by:
- aluminium framing,
- thermal breaks,
- pressure plates,
- spandrel zones,
- brackets,
- perimeter interfaces.
High-performance glass combined with poorly designed opaque and perimeter details still produces a poorly performing building envelope.
Energy performance must therefore be evaluated at system level rather than product level.
23. Treating Opening Vents as Add-On Windows
Concealed vents and outward-opening facade vents must be designed as part of the curtain wall.
The design must consider:
- sash dimensions,
- sash weight,
- hardware capacity,
- opening configuration,
- gaskets,
- drainage,
- wind actions,
- safety requirements.
An opening vent is not simply a conventional window inserted into an available curtain-wall opening.
It is an engineered component of the facade system.
24. Ignoring Galvanic Corrosion Between Different Metals
Curtain walls can contain aluminium, galvanised steel, stainless steel and different fasteners within the same assembly.
Inappropriate contact between dissimilar metals, particularly in the presence of moisture, increases galvanic-corrosion risk.
Material compatibility, protective finishes and separation materials must therefore be established during design.
The service life of a facade is influenced not only by the glass and aluminium, but also by its most vulnerable connection detail.
25. Failing to Resolve Interfaces Between Different Facade Systems
Modern buildings rarely use only one facade material.
Structural silicone or capped curtain walls can meet Aluminium Composite Panel Systems, Perforated Facade Systems, Mesh Facade Systems, Ceramic, Neolith and Sinterflex Facades, fibre cement cladding, aluminium windows and entrance canopies.
At these junctions, designers must coordinate:
drainage + thermal continuity + differential movement + substructures + installation sequence + architectural finish.
The transition between two facade systems deserves the same level of engineering attention as the systems themselves.
26. Failing to Continuously Check Alignment During Installation
Small installation errors repeated across multiple facade modules develop into substantial deviations.
During installation, teams must continuously check:
- vertical axes,
- horizontal levels,
- mullion planes,
- glass joints,
- cap alignment,
- module dimensions.
Quality control is not something performed after the facade has been completed. It is part of every stage of installation.
27. Ignoring Cleaning, Inspection and Maintenance
A glazed facade requires cleaning, inspection and occasional repair throughout its service life.
Particularly on high-rise buildings, access requirements should be considered during design.
Structural silicone joints, weather seals, gaskets, caps, opening vents and external connections should remain inspectable.
A correctly designed curtain wall must not only be installable. It must also be cleanable, inspectable, maintainable and repairable.
28. Proceeding to Full Production Without a Mock-Up or Required Performance Verification
For large or performance-critical projects, a representative facade mock-up can be used to evaluate:
- glass appearance,
- vision/spandrel uniformity,
- silicone joints,
- external caps,
- corners,
- interfaces with other materials,
- workmanship quality.
Where required by the project specification, air permeability, water penetration and structural-performance tests can also be performed on representative assemblies.
A problem identified during the mock-up stage can be corrected before it is repeated across the building.
Correct Application Process for Structural Silicone Curtain Walls
A controlled structural silicone glazing process should follow a sequence such as:
architectural modulation → wind and facade structural calculations → glass design → aluminium profile selection → anchor design → structural silicone joint design → substrate compatibility and adhesion evaluation → cassette fabrication → controlled silicone application → curing and quality control → site installation → drainage and perimeter detailing → required performance verification.
The selected silicone brand or product code alone does not make a structural glazing application correct.
The correct product must be applied to the correct substrates, with the correct joint geometry, under the manufacturer's specified conditions and quality-control procedures.
For further technical information:
EOTA – European Assessment Documents
Correct Application Process for Capped Curtain Walls
A capped curtain wall should be considered through the following coordinated sequence:
facade modulation → structural calculations → glass design → mullion/transom selection → anchors and brackets → glazing supports → EPDM gaskets → pressure plates → external caps → drainage → perimeter sealing → quality control.
Mechanical retention does not make a capped system automatically problem-free.
Errors involving pressure plates, gaskets, drainage and connections directly affect facade performance.
The basic construction principles can be examined in Capped, Semi-Capped and Structural Silicone Curtain Wall Systems.
What Should Be Considered in Semi-Capped Curtain Walls?
Semi-capped curtain walls combine characteristics of capped and structural silicone facade systems.
Depending on the architectural system, one direction can be expressed with an external cap while the perpendicular direction uses a silicone joint.
Both the mechanically retained direction and the silicone-jointed direction must therefore be detailed according to their respective system requirements.
This configuration can also be used deliberately to emphasise the horizontal or vertical rhythm of a building facade.
Examples of Structural Silicone, Capped and Semi-Capped Curtain Walls
Structural silicone and capped systems can be used independently or combined with other facade materials according to the architecture of the building.
In the Maslak Plaza – Structural Silicone Curtain Wall and A2 Composite Panel project, glazed facade areas were combined with aluminium composite cladding.
The Gülsoy Mercedes Florya project is another example of structural silicone glazing used within a commercial building facade.
Capped curtain wall systems can also be integrated with metal cladding and aluminium joinery. The completed projects section contains further examples of different facade combinations and building types.
View Optimal Mimarlık References
Structural Silicone or Capped Curtain Wall?
There is no single solution suitable for every building.
A structural silicone facade creates a more continuous external glass appearance, while a capped curtain wall introduces visible horizontal and vertical aluminium lines into the architectural composition.
Selection should consider:
architectural intent + building height + glazing module + wind actions + energy performance + maintenance + installation conditions + budget.
The appropriate system is the one that satisfies the architectural and technical requirements of the specific project.
Why Should Two Curtain Wall Quotations Not Be Compared Only by Price per Square Metre?
Two quotations for a visually similar curtain wall can represent substantially different technical scopes.
A proper comparison should include:
- aluminium system and profile series,
- calculated profile sections,
- aluminium quantities,
- glass composition,
- heat-treated or laminated glass requirements,
- Low-E and solar-control performance,
- structural silicone system,
- gaskets,
- anchors and brackets,
- fasteners,
- perimeter fire-stopping,
- spandrel construction,
- thermal and acoustic requirements,
- structural calculations,
- shop drawings,
- scaffolding, platforms or lifting equipment,
- testing,
- installation scope.
A lower price per square metre does not necessarily represent a more economical facade when important technical components are excluded from the scope.
Conclusion: System Before Glass
Glass is the dominant architectural material in structural silicone and capped curtain walls.
But glass alone does not create a safe and durable facade.
A correctly designed curtain wall is:
architecturally coordinated, structurally calculated, glazed according to project loads, securely connected to the primary structure, capable of accommodating building and thermal movement, designed to manage and drain water, detailed for air tightness, evaluated for energy and acoustic performance, coordinated with the project's fire strategy, cleanable, inspectable, maintainable and repairable.
Therefore, the first question in a curtain wall project should not be:
“Which glass and profile should we use?”
The more important question is:
“Which facade system, calculations and construction details will allow the architectural design, glass, supporting structure, wind and seismic actions, connections, water management, insulation and installation to function together correctly?”
Optimal Mimarlık approaches structural silicone, capped and semi-capped curtain wall projects as a complete process covering system selection, detailing, engineering coordination, material selection, fabrication and installation.
For system details, see Capped, Semi-Capped and Structural Silicone Curtain Wall Systems.
For project-specific services, see Curtain Wall Services.
For completed applications, visit References.
Frequently Asked Questions
Does structural silicone carry the glass in a structural silicone facade?
Structural silicone performs a structural bonding function in the designed SSG system and transfers specified actions between the glazing and its supporting frame. The method used to support and transfer the dead load of the glass depends on the selected system and its approved details.
Are structural silicone and ordinary weather-sealing silicone the same?
No. Structural glazing silicone forms part of an engineered structural bond. Weather-sealing products primarily provide environmental sealing and accommodate movement at joints. Product selection and application must follow the intended use and manufacturer's technical requirements.
Does a capped curtain wall require drainage?
Yes. Water reaching controlled internal zones of the curtain wall must be directed towards the designed drainage and discharge paths. Blocking these paths compromises facade performance.
Are structural calculations necessary for curtain walls?
Yes. Glass dimensions, mullions and transoms, anchors, brackets and connections must be evaluated according to building geometry, support conditions and applicable project loads.
Which is better: structural silicone or capped curtain wall?
The systems have different architectural expressions and connection principles. Selection depends on the building geometry, loads, facade modules, performance requirements, maintenance conditions, construction method and architectural design.
Author: Mehmet Beşe POLATKAN / Architect – YTU
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