Glazing Systems

Glazing Systems

  • 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)

Purpose: consultant-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

  1. Stick → flexible but labor-intensive
  2. Unitized → precise and fast, best for high-rises
  3. Structural → frameless, premium look, high QC need
  4. 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)

  1. Wind/pressure → transmitted to glass → to mullion/transom framing → to anchor/bracket → slab/structure.
  2. Self-weight → supported at transoms / shelf angles or by mullion vertical reactions.
  3. Thermal & seismic movement → accommodated by movement joints, slip anchors, elongated holes, compressible gaskets.
  4. 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):

  1. Performance needs: wind loads, air & water tightness, thermal goals (U & SHGC).
  2. Height & schedule: unitized for tall buildings / aggressive schedules.
  3. Budget & logistics: stick for smaller/irregular façades.
  4. Aesthetics: SSG / point fixed for frameless transparency.
  5. Maintenance & replacement strategy: ease of access for replacement; consider unitized removable panels for future access.
  6. 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.