- 1. Introduction
- 2. Summary of Major Glazing Systems
- 3. Supporting Systems
- 4. Performance Summary
- 5. Essence
- 6. Key components & sub-systems (and the role each plays)
- 7. Structural behavior & load path (concise engineering logic)
- 8. Sealing hierarchy & water management (best practice)
- 9. Movement & tolerances (practical rules)
- 10. Fabrication, QC & on-site QA
- 11. Testing & standards (must cite)
- 12. Selection criteria — how to pick a system for a project
- 13. Procurement & roles (who owns what)
- 14. Common failure modes & preventive actions
- 15. Recommended spec language (copy-paste friendly — tweak for project)
- 16. Practical annex (links & references)
- Disclaimer
Purpose: Ready overview of glazing systems.
1. Introduction
Glazing systems define how glass is fixed, supported, and sealed within a façade.
While the glass provides transparency and performance, the glazing system ensures structural integrity, weatherproofing, and aesthetics.
The choice of system depends on:
- Building height & wind load
- Site installation speed
- Maintenance strategy
- Desired façade appearance (framed vs frameless)
Every glazing system transfers load from glass → framing → anchors → structure, while ensuring air-tightness, water-tightness, and thermal stability.
2. Summary of Major Glazing Systems
Type | Description | Key Features | Advantages | Limitations / Use Case |
1. Stick Glazing System | Framing (mullions & transoms) fabricated on-site; glass installed piece-by-piece | Site-assembled, modular | Flexible for complex geometries; lower initial cost | Slower installation, quality depends on workmanship; best for low-mid rise |
2. Unitized Glazing System | Factory-assembled, pre-glazed panels (usually 1 floor high) hung on anchors | Prefabricated, high precision | Faster installation, consistent quality, minimal scaffolding | Higher logistics cost; needs cranes; ideal for high-rises |
3. Semi-Unitized Glazing System | Vertical mullions fixed on-site, panels pre-glazed and clipped | Hybrid of stick & unitized | Balanced cost & performance | Limited design complexity; common in commercial façades |
4. Structural Silicone Glazing (SSG) | Glass bonded to frame using structural silicone (2-sided or 4-sided) | Frameless exterior, clean aesthetics | Seamless façade look, weather-tight | Requires controlled factory environment; skilled application |
5. Point-Fixed / Spider Glazing | Glass held by point fittings or spider arms to a steel sub-structure | Minimal framing, maximum transparency | Iconic look; ideal for atriums, airports, showrooms | High precision, expensive detailing, limited height |
6. Panelized / Ribbon Glazing | Pre-fabricated panels spanning between columns or slabs | Integrated spandrel + vision panels | Fast site installation, repeatable design | Less flexibility; best for modular façades |
3. Supporting Systems
Subsystem | Purpose / Function |
Anchorage System | Transfers load from frame to slab/structure |
Sealants & Gaskets | Ensure weatherproofing and thermal separation |
Drainage & Pressure Equalization | Prevents water stagnation and leakage |
Thermal Breaks | Avoids condensation and improves insulation |
Spandrel Glass / Panels | Conceals floor slabs, maintains continuity |
4. Performance Summary
Parameter | Requirement / Check | Testing Standard |
Air Infiltration | ≤ 1.5 L/s·m² at 75 Pa | ASTM E283 |
Water Penetration | No leakage at 300 Pa | ASTM E331 |
Structural Performance (Wind Load) | Deflection ≤ L/175 | ASTM E330 |
Seismic / Movement Capability | Frame + sealant must allow inter-storey drift | CWCT Guidelines |
Thermal Performance | Minimize U-value, SHGC | EN 673 / EN 410 |
5. Essence
- Stick → flexible but labor-intensive
- Unitized → precise and fast, best for high-rises
- Structural → frameless, premium look, high QC need
- Point-fixed → iconic, transparent, specialized
6. Key components & sub-systems (and the role each plays)
- Mullions & transoms: primary framing members; resist wind bending and transmit loads to anchors.
- Anchors / brackets: connect frame to slab/structure — must allow movement, transfer shear and be corrosion-protected.
- Pressure plates & cover caps: mechanical retention and finished aesthetic.
- Gaskets / EPDM seals: primary water/air seals — specify shore hardness, compression set, and temperature range.
- Secondary seals (silicone, PU): weather barrier and durability; specify primer compatibility.
- Thermal breaks: minimize thermal bridging in metal frames.
- Drainage & cavities: pressure-equalized system or drainage gullets to avoid driving water into seals.
7. Structural behavior & load path (concise engineering logic)
- Wind/pressure → transmitted to glass → to mullion/transom framing → to anchor/bracket → slab/structure.
- Self-weight → supported at transoms / shelf angles or by mullion vertical reactions.
- Thermal & seismic movement → accommodated by movement joints, slip anchors, elongated holes, compressible gaskets.
- Design checks: mullion bending & deflection limits (commonly L/175 to L/240 as per project), glass edge loads, anchor shear & pullout, gasket compression. (Refer to CWCT installation guidance for movement and tolerance controls.)
8. Sealing hierarchy & water management (best practice)
- Primary seal (gasket): first line against wind-driven rain — specify continuous compression gaskets where possible.
- Secondary seal (silicone / structural sealant): backup, bond & weatherproof. For SSG, structural silicone is primary bonding.
- Drainage plane / pressure equalization: for stick systems, provide drainage paths at sill gutters; unitized systems may use internal gaskets with external cap.
- Weep holes & gutters: ensure water collected is routed out of the system.
- Testing: perform full PMU and water-penetration tests (ASTM E331 / E547 or EN equivalents) during mock-ups.
9. Movement & tolerances (practical rules)
- Allow for ±10–20 mm per floor vertical/horizontal movement in connections depending on expected thermal & seismic movement. Use slotted anchor holes allowing ± range.
- Glass edge clearances: minimum bite/setting blocks and edge clearances based on glass thickness (follow manufacturer recommendations).
- Tolerance management: strict QC on slab flatness & co-ordinate points — unitized systems demand tighter tolerances than stick systems.
10. Fabrication, QC & on-site QA
- Factory QC: dimensional checks, sealant adhesion, silicone cure, IGU gas fill verification, HST if tempering. Unitized panels should be fully tested (air/water/structural) at factory if possible.
- On-site QA: alignment checks, torque to pressure plate fasteners, continuous sealant continuity, mock-up approval (PMU & VMU). CWCT/industry guides give detailed installation procedures.
11. Testing & standards (must cite)
- EN 13830 — product standard defining curtain wall kit requirements: weather resistance, safety, energy performance (apply for Europe & widely used as reference).
- EN 410 / EN 673 — determine luminous/solar characteristics and thermal transmittance of glazing (use when specifying SHGC/VLT/U-value).
- ASTM E283 (Air leakage), ASTM E331 (Static water penetration), ASTM E330 (structural performance) — common US/International lab tests for glazing systems; use these for PMU acceptance criteria.
- CWCT guidance — practical installation & testing guidance (tolerances, drainage, sealant protocols).
(Recommendation: include explicit pass/fail criteria in contract: e.g., “Air infiltration ≤ 1.5 L/s·m² @75 Pa; No water leakage at 300 Pa; Structural deflection ≤ L/175 under design wind load.” — tie to the PMU acceptance.)
12. Selection criteria — how to pick a system for a project
Checklist (ranked):
- Performance needs: wind loads, air & water tightness, thermal goals (U & SHGC).
- Height & schedule: unitized for tall buildings / aggressive schedules.
- Budget & logistics: stick for smaller/irregular façades.
- Aesthetics: SSG / point fixed for frameless transparency.
- Maintenance & replacement strategy: ease of access for replacement; consider unitized removable panels for future access.
- Local fabrication & warranty ecosystem: availability of tested processors & applicators.
13. Procurement & roles (who owns what)
- Architect / Façade Consultant: system selection, mock-up acceptance criteria, performance targets.
- System supplier: shop drawings, compatibility data, factory testing.
- Glass processor: glass tempering/lamination/coating certification.
- Contractor / Applicator: on-site assembly, sealing, final commissioning.
- Testing agency: independent PMU & site tests (air/water/structural). (Include these roles in the contract with deliverables & acceptance tests mapped to each.)
14. Common failure modes & preventive actions
- Water leaks → poor joint detailing / blocked drainage → fix with pressure equalization + proper weeps.
- Sealant adhesion failure → incompatible primer/substrate → enforce manufacturer compatibility & adhesion tests.
- Glass breakage (NiS) → tempered glass spontaneous breakage → use Heat Soak Testing (HST) for tempered glass.
- Fastener corrosion & anchor failure → incorrect material spec / galvanic corrosion → specify stainless grades and protection.
- Thermal stress cracking → improper insulating edge, coating orientation errors → control coating face and IGU build.
15. Recommended spec language (copy-paste friendly — tweak for project)
Glazing system: Unitized curtain wall, factory-assembled, pre-glazed units to be fixed to slab face with adjustable stainless steel brackets. Units shall be pressure-equalised, have primary EPDM glazing gaskets and secondary structural silicone seals. Unit tests: air infiltration ≤1.5 L/s·m² @75 Pa, no water penetration @300 Pa, structural load per ASTM E330. Mock-up: 2.5 m × 2.5 m full-height PMU to be tested for air/water/structural performance and approved before production. Submit manufacturer’s product data, test certificates, and installation method statement.
16. Practical annex (links & references)
- EN 13830 — Curtain walling product standard.
- EN 410 / EN 673 — glazing luminous/thermal properties.
- ASTM E283 / E330 / E331 — air, structural, water standards (PMU tests).
- CWCT guidance documents — tolerance & installation best practice.
Disclaimer
Conix is an industry initiative & a neutral resource, compiled from industry references and best practices. It is not brand-specific. Always cross-check with project requirements and local codes before finalizing specifications.