Specialty Glazing and Applications

Specialized Glazing and Applications

Introduction to the Chapter

Specialized glazing encompasses all glass products and installation techniques that go beyond standard residential glazing. For the Red Seal exam, you must master not only the physical properties of these glasses, but also the regulatory requirements, structural calculation methods, and installation procedures specific to each application. This chapter covers safety glass, laminated and tempered glass, insulating glazing units, structural glazing, curtain walls, specialty glass (thermochromic, electrochromic, photovoltaic), and special applications such as guardrails and glass roofs.

Safety Glass: Tempered and Laminated

Tempered Glass (Thermal Tempering)

Tempered glass is produced through a thermal treatment that brings the glass to a temperature of approximately 620 °C to 650 °C, followed by rapid, controlled air cooling. This process creates surface compression and internal tension within the glass. The flexural strength of tempered glass is 4 to 5 times greater than that of annealed glass of the same thickness.

Typical mechanical properties:

Key points for the exam:

Laminated Glass

Laminated glass consists of two or more glass plies bonded together with a polyvinyl butyral (PVB) interlayer or resin. The interlayer holds fragments in place upon breakage, preventing the projection of debris.

Common interlayer thicknesses:

Regulatory requirements: Safety laminated glass must meet the requirements of CAN/CGSB-12.10 for impact resistance. The sandbag drop test (45 kg bag dropped from a height of 1.2 m) is the reference method.

Advantages of laminated glass:

Tempered-Laminated Combination

Tempered-laminated glazing combines both treatments: tempered glass plies bonded with a PVB interlayer. This configuration offers maximum mechanical strength and fragment retention. It is used for guardrails, skylights, glass floors, and ballistic applications.

Insulating Glazing Units (Double and Triple)

Construction and Principles

An insulating glazing unit (IGU) consists of two or three glass lites separated by spacers creating an air or gas cavity. The assembly is hermetically sealed to prevent moisture penetration and internal condensation.

Main components:

Thermal Performance

The performance of an insulating glazing unit is expressed by the thermal transmittance coefficient U (W/m²·K). The lower the U-value, the better the insulation.

Solar Heat Gain Coefficient (SHGC): the proportion of solar energy transmitted to the interior. A low SHGC (0.30 or less) is sought for hot climates; a high SHGC (0.60 and above) for cold climates.

Note: The SHGC is the American equivalent of the solar factor (g). For the exam, remember the relationship: SHGC = g × 0.87 (approximation).

National Building Code Requirements

The National Building Code of Canada (NBC 2020) imposes maximum U-values for windows and doors according to climatic zones:

Rule 9.7.3.1 of the NBC: windows must comply with thermal performance and condensation requirements. The condensation resistance factor (I) must be verified for each project.

Installation Procedures

Detecting Failures

Signs of insulating glazing unit failure include:

The typical lifespan of an insulating glazing unit is 15 to 25 years. Standard warranties cover sealant failure for 10 to 20 years.

Structural Glazing and Curtain Walls

Definitions

Structural glazing is a technique where glass is bonded to the frame or supporting structure using structural silicone. There is no mechanical pressure applied to the glass.

A curtain wall is a non-load-bearing exterior envelope that supports its own weight and wind loads, but does not support any building loads. It is attached to the main structure with anchors.

Types of Curtain Walls

Structural Silicone

Structural silicone is an elastomeric adhesive based on silicone that provides the bond between glass and frame. Its characteristics:

Application requirements:

Adhesion test (peel test): performed on a site sample, the test involves pulling the silicone at 90° and verifying cohesive failure (within the silicone mass) rather than adhesive failure (at the interface).

Wind Load Calculations

Wind pressure on glazing is calculated using the formula:

p = q × Cg × Cp

Where:

Dynamic pressure is given by:

q = 0.5 × ρ × V²

Where:

Example: For a wind speed of 40 m/s:

q = 0.5 × 1.225 × 40² = 0.5 × 1.225 × 1600 = 980 Pa

With Cg = 2.2 and Cp = 1.2:

p = 980 × 2.2 × 1.2 = 2587 Pa

Glass Thickness Based on Load

The flexural resistance of glass is calculated using the simplified formula:

σ = (3 × p × L²) / (4 × t²)

Where:

The allowable stress for annealed glass is 16 MPa (safety factor included). For tempered glass, it is 50 MPa.

Example: Panel of 1200 mm × 1500 mm subjected to a pressure of 2.6 kPa (0.0026 MPa):

σ = (3 × 0.0026 × 1200²) / (4 × t²) = (3 × 0.0026 × 1,440,000) / (4 × t²) = 11,232 / (4 × t²)

For σ = 16 MPa: t² = 11,232 / 64 = 175.5 → t = 13.2 mm → choose 15 mm glass (or 12 mm tempered).

Specialty and Smart Glass

Low-Emissivity Glass (Low-E)

Low-E glass has a microscopic coating (metal oxide) that reflects infrared radiation while allowing visible light to pass through.

Types of coatings:

Coating position in a double glazing unit: The Low-E coating is placed on the interior face of the exterior lite (surface 2) for cold climates, or on the interior face of the interior lite (surface 3) for hot climates. Surfaces are numbered from exterior to interior.

Electrochromic Glass

Electrochromic glass changes its tint upon application of an electrical voltage. It consists of several layers:

Characteristics:

Installation requirements: Wiring must comply with the Canadian Electrical Code, Part I (CE Code) (Rule 8-200 for conductors). Connections must be accessible for maintenance.

Thermochromic Glass

Thermochromic glass changes tint based on temperature. It contains a thermochromic gel or film that becomes opaque when the temperature exceeds a threshold (typically 30 °C to 35 °C). No electrical supply is required.

Photovoltaic Glass

Photovoltaic glass integrates solar cells (amorphous silicon, CdTe, CIGS) between two glass lites. It generates electricity while allowing part of the light to pass through.

Typical characteristics:

Electrical requirements: Building-integrated photovoltaic systems must comply with the Canadian Electrical Code, Part I (CE Code), Section 50 (Rule 50-000 and following).

Safety Glass for Guardrails

Glass guardrails must meet the requirements of NBC 2020, Article 3.3.1.18:

Maximum deflection calculation: The deflection of glazing under load must not exceed 25 mm or L/100 (whichever is smaller), where L is the span.

Glass Roofs and Skylights

Structural Requirements

Glass roofs must support:

Minimum slope: The slope of a glass roof must be at least 10° to ensure water runoff and prevent debris accumulation.

Safety Glass for Roofs

Glass used in glass roofs must be:

Fall protection: If the roof is accessible, a guardrail or fall protection system is required (NBC, Article 3.3.1.18).

Water Drainage

The drainage system must be designed for a 100-year rainfall event (intensity according to region). Gutters and downspouts must have sufficient capacity. The minimum 10° slope ensures rapid runoff.

Special Applications

Shower Glazing

Shower glazing must be tempered glass with a minimum thickness of 6 mm (NBC, Article 9.7.2.1). Shower doors must swing outward to allow evacuation in case of emergency.

Glass Floors

Glass floors use tempered-laminated glass with a minimum interlayer of 1.52 mm. The design load is 4.8 kPa (occupancy load) plus impact load. The glass must be slip-resistant (surface treatment or film).

Security Partitions

Security partitions (protective glazing) use laminated glass with reinforced interlayers. Classification is based on CAN/CGSB-12.11:

Aquariums and Display Cases

Public aquariums use acrylic glass (polymethyl methacrylate) or thick laminated glass. The thickness is calculated based on hydrostatic pressure:

p = ρ × g × h

Where:

Example: For a depth of 2 m:

p = 1000 × 9.81 × 2 = 19,620 Pa = 19.6 kPa

Applicable Standards and Codes

Reference Canadian Standards

NBC Requirements for Safety Glazing

Article 9.7.2.1 of the NBC requires safety glass in the following locations:

Exception: Annealed glass is permitted if the glazing is protected by a barrier (guardrail, handrail) or if the glazed area is less than 0.5 m².

Common Pitfalls to Avoid

Summary

Final exam tip: Memorize the key numerical values (minimum thicknesses, heights, loads, temperatures) and the formulas for stress and deflection calculations. Red Seal exam questions often focus on practical applications of these values. Practice solving glass thickness calculation problems and insulating glazing unit sizing problems.