Window glazing acting as guardrails and infill panels: a complete guide

We often receive questions from customers about the thickness and heat treatment of glass used in wall guardrails, as CSA A500-16 and the NBC (National Building Code) introduce a degree of uncertainty into the door and window industry. To address these concerns and help as many people as possible, we decided to create this short guide to clarify the subject and provide an overview of alternative glass options and their appropriate applications.

Understanding Glass Requirements for Walls Used as Guards

Should tempered glass be used for sealed units used as guardrails? Should only the inner pane be tempered? If we use tempered glass, can we use any thickness? These are some of the questions we frequently receive from our clients. In this article, we will discuss the different types of glass, their properties, and the factors to consider when choosing the appropriate glass for glazing used as guardrails or infill panels in guardrail conditions.

First, let's define what constitutes a guardrail condition. For a window glazing to meet a guardrail condition, the floor of the level where the window is located must be more than 600 mm above the floor or ground level on the opposite side. Next, the glazing must start at a height lower than the required guardrail height (usually 1070mm).

Typical guardrail condition

Types of Glass

Annealed Glass (Standard, Non-Tempered Glass): Annealed glass is standard float glass that has not undergone any additional heat treatment. It is four times less strong than tempered glass and, when broken, tends to shatter into large, sharp shards, posing a safety risk.

Heat-Strengthened Glass: Heat-strengthened glass undergoes a heating and cooling process that makes it approximately twice as strong as annealed glass, but still half as strong as tempered glass. When broken, it shatters into large pieces, similar to annealed glass; however, this type of glass cannot replace tempered glass in doors, for example.

Tempered Glass: Tempered glass is heat-treated to be approximately four times stronger than annealed glass. It is designed to withstand higher loads and, when broken, shatters into small fragments, reducing the risk of injury.

Evaluating Alternatives

Many clients approach us to explore more cost-effective options for sealed units acting as railings, such as annealed or heat-strengthened glass, or thinner tempered glass. At a very low cost, we can help them validate different glazing compositions to support the railing loads on any building. We can also guide them on code and standard compliance. Don't wait any longer; join dozens of other door and window manufacturers and choose peace of mind.

Infill Panel vs. Glass Railing

When a transom is located at a height equal to or less than the required railing height, the glass beneath the transom acts as an infill panel. Infill panels have lower load requirements, which can allow the use of thinner glass than glazing that must support the railing loads.

Please feel free to contact us for a quote if you have any questions. At very little cost, you can validate your assumptions and thus reduce the risks.

Infill Panels and the National Building Code (NBC)

⚠ Important Information:

Considering the reference to Part 9 for residential buildings in Quebec via section 3.3.4.7.1;

Considering also the presence of section 9.8.8.7 which states that the glass panels of guardrails must be made of safety glass (tempered or laminated);

And since the distinction between walls acting as guardrails and guardrails (balustrades) is not currently entirely clear;

We believe that the use of non-tempered glass (on the interior side) in windows acting as guardrails should be avoided, at least for glazed portions whose sill is below the required guardrail height, pending the new version of the CAN/CGSB-12.20 standard which will clarify this aspect.

Understanding Guardrail Requirements in the National Building Code

For Part 9 buildings, refer to section 9.8.8.1 (points 6, 7, and 8) for the application of guardrail loads at window level. The areas affected are primarily stairways, ramps, landings, and common areas. Note, however, that the code is a minimum requirement and that Appendix A-9.8.8.1 states that a wall should be strong enough to prevent a person from falling. Although the appendices are not part of the code, it should be noted that a window starting near the floor on the interior side and without a horizontal rail could pose a significant safety risk. Note that the 900 mm height in section 9.8.8.1.7 is for an inward fall and does not generally apply to windows.

Otherwise, for Part 3 buildings, if the glazing of the fenestration products starts less than 1070mm from the floor and there is a possibility of a drop of more than 600mm (between the interior floor and the ground on the exterior side), the glazing must be validated to withstand the guardrail loads according to 4.1.5.16, regardless of the use or location, so this applies even in dwellings for buildings covered by Part 3 (more than 3 stories or more than 600m² footprint); refer to comment i-102 of the 2020 NBC User Guide.

Transom Height and Its Effects

The transom height is crucial in determining whether the glass above and below will act as a guardrail or a filler panel. For example:

1. If the center of the transom is 1070 mm from the finished interior floor, the glazing above will not act as a guardrail, and the glazing below the transom will act as a filler panel.
2. If the transom is lower, say at 800 mm, the glazing below will also act as a filler panel, but the glazing above will act as a guardrail.

You can also refer to our diagram for guidance ↓

It is important to note that for a glazing unit, the concept of redundancy is not required, so only the inner pane of glass will be considered. The outer pane, however, must be able to withstand wind loads.

Redundancy and Outer Pane of Glass

The CAN/CGSB-12.20-M89 standard, which governs glazing design in Canada and is cited in sections 4.3.6.1 and 9.6.1.3 of the building code, requires redundancy in case of breakage (see A3.1 and A5.1). What exactly is redundancy? It is an alternative route in case of glass breakage, much like a seatbelt in a car. This principle is used for structural glass, in the aviation industry, and more. Thus, for insulating glass acting as a guardrail, the outer pane of glass must also be able to support a portion of the guardrail's load. This redundancy is ensured by checking the outer pane of glass so that it can bear part of the load of the guardrail. In this way, if the inner pane has a defect or a scratch and breaks under a much lower stress, safety can be ensured by the outer pane. For the outer pane of a sealed unit acting as a guardrail, the applied load is lower. For this reason, the outer pane can generally be thinner than the inner pane and still meet the guardrail load requirements.

Glazing Testing

Because glass has variable mechanical properties depending on defects in its mass, surface scratches, or edge nicks, etc., tests are not relevant for glass. The figure below illustrates the maximum breaking stress for 740 glass samples tested under the same load and holding conditions.

Building Code and Tempered Glass

Although the building code does not explicitly require tempered glass for insulating glass units acting as guardrails, at least for buildings covered by Part 3, annealed glass generally cannot withstand these loads. Since point loads generate relatively high localized stresses, and annealed glass is four times less strong than tempered glass, annealed (non-tempered) glass is not a viable option for sealed units acting as guardrails.

Practical Examples

1. A 1000mm x 1000mm sealed unit composed of two 6mm thick annealed glass panes would result in 260% strength utilization on the inner pane and 195% on the outer pane. 100% is the maximum capacity of the glazing.
2. For a 500mm x 1000mm sealed unit, the inner pane would be at 212% strength with the same composition (2 x 6mm annealed glass).

These examples show that even with 6mm annealed (non-tempered) glass, the glazing limit is far exceeded. At 212%, we are at more than twice the strength limit of annealed (non-tempered) glass. This is why non-tempered glass is not an option for a sealed unit in a window acting as a guardrail.

Use tempered glass

Caution: Tempering a sealed 2x3mm unit is not sufficient to support the guardrail loads. In 99% of cases, 3mm tempered glass will not be able to support the guardrail loads. Therefore, it is essential to validate the suitability of the glass based on the dimensions of the glazing, its position, and the wind loads on the building, as some wind loads combine with the guardrail load.

Conclusion

As this article demonstrates, annealed (non-tempered) glass cannot withstand the loads of guardrails, making tempered glass the preferred choice for safety reasons. However, the thicknesses of the inner and outer panes (redundancy) must be adjusted according to the criteria mentioned above; this must be validated on a project-by-project basis. Particular attention should be paid to the use of tempered glass for the outer layer in high-rise buildings near pedestrian zones. Please contact us for further details.

Regarding infill panels, the loads are lower, and redundancy is not necessary. Therefore, the most economical option is to position a horizontal transom at the required guardrail height (generally 1070 mm). In this way, the glazing above will only need to withstand wind loads, and the glazing below will only need to be tempered in its inner layer. It is essential to carefully consider the type of glass, thickness, and heat treatment when selecting glazing for a window used as a guardrail or infill panel. Understanding the guardrail requirements of the National Building Code and the differences between infill panels and guardrails can help you make informed decisions that prioritize safety while remaining cost-effective.

© Glaspex Inc., 2026. All rights reserved. Unauthorized reproduction of this article or its contents is prohibited. This article is based on our interpretation of codes and standards. This article and its contents do not constitute professional advice and are provided for informational purposes only. This is an overview that does not necessarily cover all technical aspects and/or special cases. Glaspex, LSVM, or the author of this article will not be held liable for any decisions made in connection with this article. Reuse of this article or its contents for professional purposes, including engineering purposes, is prohibited. Note that each project has specific requirements and must be approved by an engineer. Also note that this applies to all articles published previously and subsequently.