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CAN CGSB 12.2-M91 (2017): Technical Specifications for Flat, Transparent Sheet Glass
A Comprehensive Guide to the Canadian Standard for Flat Glass in Building Glazing and General Applications
Scope and General Overview
CAN CGSB 12.2-M91 (2017), developed by the Canadian General Standards Board (CGSB), specifies requirements for flat, transparent sheet glass intended for general glazing, picture framing, and other applications where optical clarity and dimensional consistency are essential. This standard covers both single-strength and double-strength sheet glass, as well as other nominal thicknesses, and addresses the criteria for quality, thickness tolerances, allowable defects, and visual distortion. Originally published in 1991 and reaffirmed in 2017, it remains a key reference for glass manufacturers, distributors, and building regulators across Canada.
The standard applies to clear, flat glass produced by the sheet (drawing) process, as distinct from float glass or plate glass. While float glass has largely replaced drawn sheet glass in modern construction, the standard still applies to legacy products, specialty glazing, and certain industrial applications. The scope of the standard includes all sheet glass with nominal thicknesses from 1.5 mm to 6.0 mm.
Technical Requirements and Material Specifications
Thickness Designations and Tolerances
The standard defines specific nominal thicknesses and tolerances for flat, transparent sheet glass. The thickness designation corresponds to the approximate weight per unit area (e.g., “single strength” is approximately 2.5 mm, “double strength” is approximately 3.0 mm). The allowed deviation from nominal is strictly controlled to ensure consistent performance in glazing.
| Nominal Designation | Nominal Thickness (mm) | Thickness Tolerance (mm) | Maximum Waviness (per 300 mm) |
|---|---|---|---|
| Single Strength (SS) | 2.5 | ±0.20 | 0.40 mm |
| Double Strength (DS) | 3.0 | ±0.25 | 0.40 mm |
| Medium | 4.0 | ±0.30 | 0.30 mm |
| Heavy | 5.0 | ±0.35 | 0.25 mm |
| Extra Heavy | 6.0 | ±0.40 | 0.25 mm |
Note: Thickness tolerances and waviness limits are essential for ensuring proper fit in glazing channels and minimizing optical distortion after installation.
Optical Quality and Visual Defects
The standard includes detailed requirements for visual inspection of glass sheets. Defects such as bubbles, stones, knots, scratches, and string lines are categorized by size, frequency, and location within the sheet. A grading system may allow minor defects in peripheral areas while specifying stricter limits for the central vision area. Distortion due to waviness or thickness variation is controlled to maintain acceptable optical clarity.
Tip: When specifying glass for high-visibility storefronts or display cases, consult the defect allowance tables in CAN CGSB 12.2-M91 (2017) to select a quality grade appropriate for the application.
Workmanship and Finish
All glass must be free from cracks, chips at edges, and open bubbles. Cut edges must be clean and free from deep checks. The standard also addresses permissible bowing and squareness deviations for cut pieces.
Implementation and Testing Highlights
To claim compliance with CAN CGSB 12.2-M91 (2017), manufacturers must implement a quality control program that encompasses raw material verification, process control during forming, and final inspection of cut sheets. Testing involves both dimensional measurement and visual inspection under specified lighting conditions.
Dimensional Testing
Thickness is measured with a micrometer or dial gauge at multiple points along the sheet edges and center. Length and width are measured with a steel rule or calibrated tape; squareness is checked by measuring diagonal differences. Waviness is assessed using a straightedge and feeler gauge.
Visual Inspection
Visual inspection for defects is performed under controlled lighting (diffuse transmitted light) against a black background. The inspector identifies and counts defects per unit area, comparing against the thresholds in the standard.
Important: Visual inspection is subjective to some degree. It is recommended to have at least two trained inspectors for critical quality verifications, and to reference limit samples when possible.
Compliance and Quality Assurance Notes
While CAN CGSB 12.2-M91 (2017) is not incorporated by reference in all Canadian building codes, it is widely recognized as a benchmark for sheet glass quality. Many provincial regulators and municipal building departments accept compliance with this standard as satisfying the performance requirements for glazing materials listed in the National Building Code of Canada (NBC).
Manufacturers intending to label their product as meeting CAN CGSB 12.2-M91 should maintain a documented quality management system and retain records of inspection results. Third-party certification, such as that provided by certified laboratories, is advisable for significant projects.
Compliance Tip: Ensure that the glass supplier provides a certificate of conformance referencing the standard number and reaffirmation year (2017) to demonstrate traceability.
Non-Compliance Risk: Use of sheet glass that does not meet the thickness tolerance or defect limits of the standard can lead to premature breakage, seal failure in insulating glass units, and increased liability in the event of glazing failure.
The standard also notes that it is subject to periodic review by the CGSB committee. Users should verify that they are using the latest reaffirmation or revision. The 2017 reaffirmation did not introduce technical changes but confirmed that the standard remains current.
Q: What glass products are covered under CAN CGSB 12.2-M91 (2017)?
A: The standard covers flat, transparent sheet glass produced by the sheet drawing process. It includes nominal thicknesses from 1.5 mm to 6.0 mm, commonly designated as single strength (SS), double strength (DS), medium, heavy, and extra heavy. It does not cover float glass, plate glass, or wired glass.
A: The standard covers flat, transparent sheet glass produced by the sheet drawing process. It includes nominal thicknesses from 1.5 mm to 6.0 mm, commonly designated as single strength (SS), double strength (DS), medium, heavy, and extra heavy. It does not cover float glass, plate glass, or wired glass.
Q: What are the key quality criteria for visual defects?
A: The standard limits the number and size of bubbles, stones, knots, scratches, and string lines. Defects in the central viewing area are subject to stricter limits than those near edges. The glass must be essentially free of open bubbles and cracks.
A: The standard limits the number and size of bubbles, stones, knots, scratches, and string lines. Defects in the central viewing area are subject to stricter limits than those near edges. The glass must be essentially free of open bubbles and cracks.
Q: How can a manufacturer or supplier demonstrate compliance with the standard?
A: Compliance is typically demonstrated through a quality control program that includes regular thickness measurements, visual inspection per the standard’s defect tables, and record keeping. A certificate of conformance may be issued. For independent validation, third-party testing by an accredited laboratory can be arranged.
A: Compliance is typically demonstrated through a quality control program that includes regular thickness measurements, visual inspection per the standard’s defect tables, and record keeping. A certificate of conformance may be issued. For independent validation, third-party testing by an accredited laboratory can be arranged.
Q: Does the 2017 reaffirmation change any technical requirements from the original 1991 version?
A: The 2017 reaffirmation confirmed the existing requirements without technical changes. It ensures the standard remains current and recognized for compliance purposes. Users should always reference the reaffirmation year in specifications to avoid ambiguity.
A: The 2017 reaffirmation confirmed the existing requirements without technical changes. It ensures the standard remains current and recognized for compliance purposes. Users should always reference the reaffirmation year in specifications to avoid ambiguity.
Last revised: 2026. This article is for informational purposes; always consult the official CGSB publication for complete details.