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Choosing the Right Seal for a High-Performance Glazed Facade

The seal around a glazed facade affects far more than its appearance. It helps control water, air, noise, movement, heat loss and the long-term stability of the building envelope. Selecting between a siliconised seal and structural silicone glazing therefore requires a clear understanding of how the facade is designed to transfer loads and resist weather.

These solutions can look similar once installed, but they perform different roles. A siliconised gasket is generally a preformed seal installed within a pressure-glazed or mechanically retained system. Structural silicone glazing uses a specially formulated adhesive to bond the glass to a framing system, transferring defined loads through the cured silicone joint.

For developers, architects and main contractors, the correct decision should be made during facade design rather than left to the installation stage. Glass type, panel size, wind loading, movement, drainage, fire strategy, maintenance access and compatibility between adjacent materials all influence the specification.

Understand The Difference In Function

A siliconised seal is usually based on a preformed elastomeric gasket, commonly EPDM or a related material, with a silicone treatment, coating or lubricant that assists installation and improves sealing performance. The gasket is compressed mechanically into a glazing pocket. Retaining beads, pressure plates or other framing components hold the glass in place, while the gasket provides the weather and air seal.

This approach is widely used in curtain walling, windows, doors and rainscreen interfaces. It is relatively fast to install, can be replaced during maintenance and offers a predictable solution when the frame has been designed around mechanical retention. The glass load is primarily carried by setting blocks, beads or pressure plates rather than by the seal itself.

Structural silicone glazing, often abbreviated to SSG, follows a different principle. A compatible silicone adhesive forms a continuous bond between the glass and a supporting frame or carrier. The joint is designed to resist wind load and, depending on the system, may contribute to the transfer of dead load and other forces. Mechanical retainers may still be required for safety, restraint or system-specific reasons, but they are not the primary weather-sealing mechanism in the same way as a conventional gasket.

Assess Weather And Movement Requirements

Both systems can provide strong resistance to wind-driven rain when correctly designed and installed. The key difference is how they accommodate movement. A gasket relies on compression and the elasticity of its profile, while a structural silicone joint relies on the cured adhesive maintaining its bond and elastic performance over the expected movement range.

Facade movement may arise from thermal expansion, inter-storey deflection, frame tolerances, glass deformation and differential movement between materials. Silicone is highly elastic, which makes it useful for movement joints and bonded glazing applications. However, the joint must have the correct width and depth, and the silicone must be able to extend and compress without excessive stress.

A siliconised gasket is often the practical choice where regularised frame profiles and replaceable components are priorities. It can also be advantageous where glazing units may need to be removed without cutting through a bonded joint. Structural silicone may offer cleaner external lines and reduced sightlines, but its performance depends heavily on joint geometry, curing conditions and strict control of substrate preparation.

Weathering should be considered as part of the complete envelope rather than as an isolated seal detail. The glazing interface must work with flashings, drainage paths, cavity barriers, insulation and membranes. Designers should also review vapour barrier guidance when developing junctions between glazing, cladding and internal finishes.

Consider Appearance, Thermal Performance And Acoustics

Siliconised gasket systems usually show a visible frame, pressure plate or bead at the external face. This can suit commercial buildings where a modular curtain wall grid is part of the architectural language. Gaskets are available in different colours, but the visual result remains influenced by the profile depth, joint lines and retention method.

Structural silicone glazing can create a more flush facade with narrower apparent joints and less visible framing. This is often selected for premium commercial, residential, retail and civic schemes where uninterrupted glass surfaces are important. The visual benefit must be balanced against more demanding design controls and the need for specialist installation.

Thermal performance depends on the whole framing system, not simply on the seal material. A thermally broken aluminium profile, insulated spandrel zone, warm-edge spacer, suitable glass specification and correctly designed perimeter interface will usually have a greater effect on U-values than the choice between two seal types alone. Air leakage and condensation risk also depend on continuity through the frame and surrounding wall.

Acoustic performance follows a similar principle. Glass thickness, laminated interlayers, unit configuration, frame design and installation tolerances all contribute. A structural silicone joint can help reduce visible framing and may support a highly sealed facade, but it does not automatically produce better acoustic results than a well-designed gasketed system.

Compare The Main Selection Factors

The correct choice depends on the project’s risk profile, appearance, access requirements and construction sequence. A system that performs well on a low-rise residential building may be unsuitable for a tall commercial facade with high wind pressures and significant floor movement.

Selection factor Siliconised gasket seal Structural silicone glazing
Primary function Compressed weather and air seal within a mechanically retained system Bonded connection and weather seal between glass and supporting frame
Glass retention Mechanical retention, beads, pressure plates and setting blocks Silicone bond, often supported by secondary safety or restraint measures
External appearance More visible framing, beads or pressure plates Cleaner, flush appearance with reduced visible retention
Movement response Elastic gasket compression and profile flexibility Elastic movement within a designed silicone joint
Installation control Profile placement, corner joints, compression and drainage are critical Substrate preparation, primer, joint dimensions, adhesion and curing are critical
Replacement and repair Gaskets and glass are generally easier to remove or replace Bonded units require controlled cutting, cleaning and resealing
Design dependency Relies on compatible proprietary frame and gasket profiles Requires engineered joint sizing, tested materials and approved procedures
Typical suitability Standard curtain walling, windows and robust modular facades Feature facades, flush glazing and visually demanding bonded systems

Neither option should be selected solely because it appears cheaper or produces a smaller sightline. Whole-life cost may be influenced by fabrication, access, inspection, replacement, testing, remedial work and programme constraints. A facade contractor with experience in glazing and cladding can help coordinate these factors before procurement.

Check Compatibility And Compliance

Silicone products must be compatible with glass coatings, insulating glass unit edge seals, spacers, gaskets, setting blocks, paints, powder coatings, membranes and adjacent cladding materials. Contamination or chemical interaction can weaken adhesion, stain surfaces or reduce service life. Compatibility testing should be required where materials come from different manufacturers or where the proposed combination has not already been approved.

Structural silicone glazing requires documented evidence that the selected adhesive is suitable for the intended application. This may include manufacturer approvals, project-specific adhesion and compatibility tests, and calculations for wind load, glass weight and movement. The design should identify the required bite, joint depth, cure time and substrate preparation method.

For mechanically retained glazing, attention should turn to gasket compression, corner joints, end laps, drainage openings and the continuity of seals at interfaces. A correctly specified gasket can underperform if it is stretched, cut inaccurately, fitted with open corners or compressed outside the manufacturer’s tolerances.

The wider regulatory context also matters. The facade should be assessed against relevant UK Building Regulations, project performance specifications, fire requirements, safety provisions and applicable product standards. Structural silicone should never be treated as a decorative sealant, and a siliconised gasket should not be assumed to provide structural restraint unless the system documentation explicitly states that it does.

Plan Installation And Quality Control

Site conditions are especially important for structural silicone. Surfaces must be clean, dry and prepared according to the adhesive manufacturer’s instructions. Temperature, humidity, curing time and protection from movement during cure all need to be controlled. The glazing unit should not be loaded or exposed to service conditions before the bond has achieved the required strength.

Quality assurance should include batch tracking, substrate checks, bead inspection and records of application conditions. Where the system requires it, adhesion tests and peel tests should be completed at defined intervals. The installer should also confirm that silicone joints are continuous, free of voids and correctly tooled without damaging adjacent finishes.

Gasket installation has its own quality risks. Profiles must be cut and joined correctly, with sufficient compression at corners and around changes in direction. Glass should sit on correctly positioned setting blocks, and drainage routes must remain open. Stretching a gasket during installation can cause shrinkage at corners later, creating leakage or visible gaps.

Inspection should continue after glazing is complete. Water testing, air permeability checks, visual reviews and interface inspections can identify defects before internal finishes conceal them. Clear records at handover help the building owner understand which seals are bonded, which are replaceable and how future repairs should be carried out.

Make The Decision At The Design Stage

A practical selection process starts with the building’s performance brief and architectural intent. The team should establish whether the glazing is intended to be mechanically retained, bonded, or used in a hybrid system. It should then confirm the load path, movement allowances, drainage strategy, thermal targets and access arrangements.

The following recommendations help keep the decision evidence-based:

An integrated package can reduce gaps between design intent, material procurement and site installation. Bak Cladding Solutions provides integrated envelope services covering cladding, roofing and architectural glazing, allowing these interfaces to be reviewed as part of one coordinated building envelope.

The most suitable seal is the one that provides the required performance with an achievable installation method and a realistic maintenance plan. Siliconised gaskets offer proven mechanical retention and easier replacement, while structural silicone glazing can deliver a refined appearance and flexible bonded performance when engineered correctly.

Bring the glazing, cladding and roofing teams into the discussion early, before frame profiles and facade details are fixed. A project-specific review of loads, movement, material compatibility, testing and handover requirements will help turn the preferred seal type into a durable, compliant facade solution.