Glazing Systems and Components

Glazing Systems and Components

Chapter Introduction

This chapter covers all glazing systems and their components as assessed in the Red Seal exam for the glazier trade. You must master the terminology, design principles, installation methods, dimension calculations, and Canadian regulatory requirements. This chapter is structured to follow the logical progression of the trade: from glazing types to fastening systems, including clearance calculations and tolerances.

Glazing Types and Their Applications

Annealed Glass (Float Glass)

Annealed glass is the base product produced by the float process (floating on a tin bath). It is cooled slowly to eliminate internal stresses. Its nominal flexural strength is approximately 41 MPa (6,000 psi), but this theoretical value is never used in practical calculations due to the presence of micro-cracks on the surface. In practice, an allowable stress of 17 MPa is used for wind-load glass calculations.

Annealed glass breaks into long, sharp fragments. It must never be used in applications where there is a risk of human injury unless it is tempered or laminated. Its nominal thickness ranges from 2 mm to 25 mm, with common thicknesses being 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 15 mm, 19 mm, and 25 mm.

Tempered Glass (Safety Glass)

Tempered glass undergoes a thermal treatment (heating to approximately 650 °C followed by rapid air cooling). This process creates surface compression and internal tension. Its strength is 4 to 5 times greater than annealed glass of the same thickness. The allowable flexural stress is approximately 68 MPa.

Key characteristics:

Laminated Glass

Laminated glass consists of two or more glass sheets (annealed, tempered, or heat-strengthened) bonded together with an interlayer of polyvinylbutyral (PVB), ionomer (SentryGlas®), or resin. The interlayer holds fragments in place upon breakage, preventing debris from falling.

Typical applications:

The standard PVB interlayer thickness is 0.38 mm (0.015 in) or multiples: 0.76 mm, 1.14 mm, 1.52 mm. For guardrails, a minimum interlayer of 1.52 mm is generally required.

Heat-Strengthened Glass

Heat-strengthened glass is thermally treated but cooled more slowly than tempered glass. Its strength is approximately 2 times that of annealed glass. It breaks into larger fragments than tempered glass but remains stronger than annealed glass. It is used in applications where increased strength is needed without the safety requirements of tempered glass, particularly in large insulating glazing units.

Coated Glass (Solar Control Glass, Low-Emissivity)

Coated glasses are annealed or tempered glasses onto which thin layers of metals or metal oxides are deposited. Two types are distinguished:

Low-emissivity (Low-E) glasses reduce heat transfer by radiation. The typical emissivity value is 0.04 to 0.20 (compared to 0.84 for clear glass). The solar heat gain coefficient (SHGC) and visible light transmittance (VLT) are critical parameters for glazing selection.

Insulating Glass (Double and Triple Glazing)

Insulating glass (IG) consists of two or three glass sheets separated by spacers creating a cavity filled with dry air or gas (argon, krypton). The typical cavity is 12 mm or 16 mm. Noble gases improve thermal performance:

The U-value (thermal transmittance coefficient) of a standard insulating glazing unit (6 mm clear + 12 mm air + 6 mm clear) is approximately 2.8 W/m²·K. With Low-E glass and argon, values of 1.4 W/m²·K can be achieved. In triple glazing with two Low-E coatings and krypton, values drop to 0.7 W/m²·K.

Glazing System Components

Sealants and Caulking

Sealants are classified according to their modulus of elasticity and movement capability:

Structural silicone is used to bond glass to the frame without mechanical support. It must be applied under controlled conditions (temperature between 5 °C and 40 °C, relative humidity < 80%). The minimum structural joint width is 6 mm, and the minimum depth is 6 mm.

Profiles and Frames

Frames can be made of aluminum, steel, wood, PVC, or composite materials. For the exam, you must know aluminum profiles:

Spacers for Insulating Glass

Spacers maintain the gap between glass sheets and contain the desiccant (molecular sieve or silica gel) that absorbs residual moisture. Common types:

The spacer width determines the cavity width. Standard widths are 6 mm, 9 mm, 12 mm, 15 mm, 16 mm, and 20 mm. The minimum width for acceptable thermal performance is 12 mm.

Setting Blocks and Location Blocks

Setting blocks support the weight of the glazing. They are placed at the quarter points of the glazing width from each bottom edge. Their minimum width equals the glazing thickness plus 3 mm, and their length ranges from 50 mm to 100 mm depending on weight.

Location blocks hold the glazing in lateral position. They are placed on each side edge, approximately 150 mm from the bottom corners. They must never support the weight of the glazing.

The block material must be compatible with the sealant and glass. Neoprene, EPDM, or silicone are commonly used. Wood and metal are prohibited because they cause stress concentrations.

Calculations and Dimensions

Glazing Clearance Calculation (Perimeter Sizing)

Glazing clearance is the space between the glass edge and the bottom of the rebate. It must accommodate thermal expansion of the glass and building movements. The basic formula:

Minimum clearance = (Thermal expansion coefficient of glass) × (Glazing dimension) × (Maximum ΔT) + Manufacturing tolerance

The thermal expansion coefficient of glass is 9 × 10⁻⁶ m/m·°C (0.000009 per °C). For a 1,500 mm glazing with a ΔT of 50 °C:

Expansion = 1,500 mm × 0.000009 × 50 °C = 0.675 mm

The recommended minimum clearance is 3 mm per side for glazing under 1 m², and 5 mm per side for larger glazing. For insulating glass units, the clearance must be increased by 1 mm per side to compensate for internal pressure.

Allowable Deflection Calculation

Deflection (deformation) of glazing under wind load is limited to L/175 where L is the smallest dimension of the glazing, with a maximum of 25 mm. For a 1,200 mm × 1,500 mm glazing, the maximum deflection is:

Maximum deflection = 1,200 mm / 175 = 6.86 mm

This limit is important to avoid glazing failure and loss of weathertightness.

Wind Pressure Calculation

Wind pressure is calculated according to the National Building Code of Canada (NBCC). The simplified formula:

P = q × Ce × Cg × Cp

Where:

For the exam, you must know that wind pressure increases with building height and that edge zones (corners) experience higher pressures than central zones.

Glazing Strength Calculation

The strength of glazing under wind load is determined from the allowable stress and the section modulus. For a rectangular glazing simply supported on all four sides:

σ = (k × P × a²) / t²

Where:

For annealed glass, σ must be ≤ 17 MPa. For tempered glass, σ must be ≤ 68 MPa.

Applicable Standards and Codes

National Building Code of Canada (NBCC)

The NBCC (Part 9 for small buildings, Part 4 for large buildings) imposes requirements on:

CAN/CGSB Standards

The Canadian General Standards Board (CGSB) standards define manufacturing and performance requirements:

CSA A440 Standard

The CSA A440 (Windows) standard specifies performance requirements for windows and sliding doors. Classifications are based on:

For the exam, remember that the complete classification is written in the form A3-B7-C5-D5 (example of maximum performance).

Installation Procedures

Installing Glazing in a Frame

The standard procedure includes:

Structural Glazing Installation

Structural glazing bonds the glass to the frame using silicone only. Requirements are:

Insulating Glass Unit Installation

Insulating glass units must be handled with care to avoid damaging the perimeter seal. Rules:

Common Pitfalls to Avoid

Summary

This chapter covers the fundamentals of glazing systems. Make sure you master clearance and deflection calculations, NBCC requirements, and CSA A440 classifications before moving on to the following chapters on curtain walls and guardrails.