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ISO 28278-1: Glass Products for Structural Sealant Glazing
Requirements for supported and unsupported monolithic and multiple glazing in SSG systems
Understanding Structural Sealant Glazing and ISO 28278-1
ISO 28278-1:2011 specifies requirements for the suitability of supported and unsupported glass products used in structural sealant glazing (SSG) systems. Developed by ISO/TC 160 (Glass in building), this standard addresses only soda-lime silicate glass and focuses on verifying that glass products meet the rigorous demands of SSG applications where the sealant bears structural loads. The standard is an essential reference for architects, facade engineers, and building envelope consultants worldwide.
SSG systems transfer wind loads and other forces from the glass to the building framework exclusively through the structural silicone sealant — there are no mechanical fasteners penetrating the glass surface, creating the seamless aesthetic that defines modern curtain-wall architecture.
The standard covers both monolithic and laminated glass products, as well as insulating glass units (IGUs), for use in supported (mechanical restraint present) and unsupported (fully bonded) configurations. Key parameters include dimensional tolerances, edge quality, glass shape limitations, and UV radiation resistance of the sealant-glass interface. The standard works in conjunction with ISO 28278-2 which provides the assembly rules for actual installation.
| Glass Configuration | Description | Typical Applications |
|---|---|---|
| Supported monolithic | Single pane with mechanical support | Low-rise curtain walls |
| Unsupported monolithic | Single pane, fully bonded | High-rise facades |
| Supported IGU | Insulating unit with mechanical restraint | Energy-efficient buildings |
| Unsupported IGU | Insulating unit, fully bonded | Modern high-performance glazing |
| Laminated glass | Multiple panes with interlayer | Safety and security glazing |
Engineering Design Insights for SSG Glass Selection
The standard establishes that structural, weatherproofing, and sealant products for SSG are primarily based on organo-siloxane (silicone) polymers. Engineers must verify that glass products conform to the applicable product standards while also meeting supplementary SSG-specific requirements for UV stability, adhesion durability, and tolerance consistency. The glass must be compatible with the structural sealant and must not contain surface contaminants that could compromise the adhesive bond.
ISO 28278-1 explicitly notes that where there is a risk of earthquake, the sealant design may not be sufficient to resist the loads, and complementary mechanical arrangements may be necessary. This is a critical safety consideration for seismic regions where additional restraint devices should be specified.
UV radiation testing is specified for three distinct exposure situations: Situation 1 (IGU with UV exposure on the seal), Situation 2 (IGU with UV-protected seal), and Situation 3 (laminated or monolithic glass). Each situation requires different test protocols for assessing sealant-glass adhesion after UV ageing. The standard references test methods including ISO 527-3 for tensile properties and ASTM C1184 for structural silicone specifications. These tests ensure long-term durability of the bond under real-world environmental conditions.
Design Calculation Methodology
Clause 8 provides the calculation framework for determining glass thickness based on the support conditions, and the critical dimension of the outer seal height for IGUs. For unsupported glazing, the seal dimensions must be calculated considering wind load, dead load, thermal movement, and sealant modulus. The standard provides formulas relating sealant bite depth and width to the anticipated stresses, enabling engineers to size the structural seal for the specific project conditions and local building code requirements.
The Annex system in ISO 28278-1 is extensive, covering assembly requirements (Annex A), structural/UV-resistant sealant specifications (Annex B), factory production control (Annex E), and IGU outer seal category differentiation (Annex F). Engineers should consult the relevant annex for their specific application. Annex B is particularly important for specifying the correct silicone sealant grade.
Quality Assurance and Factory Production Control
ISO 28278-1 mandates that sealant manufacturers provide documented evidence of product suitability, including initial type testing results. The factory production control requirements (Annex E) ensure that sealant production maintains consistent quality through regular testing of tensile strength, elongation, hardness, density, and UV resistance. This systematic approach to quality assurance is essential for maintaining the safety and performance of SSG systems over their service life, which typically exceeds 25 years for modern installations.
Frequently Asked Questions
Q1: What glass types are covered by ISO 28278-1?
A: Only soda-lime silicate glass is within scope. This includes monolithic, laminated, and insulating glass units (IGUs). Plastic glazing is explicitly excluded from the standard.
A: Only soda-lime silicate glass is within scope. This includes monolithic, laminated, and insulating glass units (IGUs). Plastic glazing is explicitly excluded from the standard.
Q2: How does ISO 28278-1 relate to ISO 28278-2?
A: Part 1 covers the suitability of glass products for SSG, while Part 2 provides assembly rules for installation and bonding. Together they form a comprehensive framework for SSG system quality.
A: Part 1 covers the suitability of glass products for SSG, while Part 2 provides assembly rules for installation and bonding. Together they form a comprehensive framework for SSG system quality.
Q3: What is the significance of the three UV exposure situations?
A: The three situations reflect different real-world configurations: exposed IGU seals, protected IGU seals, and monolithic/laminated glass. Each has different UV degradation risks requiring tailored testing protocols.
A: The three situations reflect different real-world configurations: exposed IGU seals, protected IGU seals, and monolithic/laminated glass. Each has different UV degradation risks requiring tailored testing protocols.
Q4: Can non-silicone sealants be used in SSG systems?
A: Yes, ISO 28278-1 does not preclude other sealant types, provided they can demonstrate suitability for service according to the standard and are used following the manufacturer’s recommendations.
A: Yes, ISO 28278-1 does not preclude other sealant types, provided they can demonstrate suitability for service according to the standard and are used following the manufacturer’s recommendations.
