2024 IBC Significant Structural Changes Part 8-Glass and Glazing (IBC Chapter 24)

By John “Buddy” Showalter, PE, and Sandra Hyde, PE

This multi-part series discusses significant structural changes to the 2024 International Building Code (IBC) by the International Code Council (ICC). This article includes an overview of changes to IBC Chapter 24 on glass and glazing. Only a portion of the chapter’s total number of code changes is discussed in this article. More information on the code changes can be found in the 2024 Significant Changes to the International Building Code available from ICC.

Loads on Glass Guards and Handrails

IBC Section 2407 includes uniform regulations identifying the specific types of safety glazing that may be used structurally. Laminated tempered and laminated heat-strengthened glazing are the only types considered by the code to be structurally adequate under all conditions of installation. Single-layer tempered glass is acceptable under limited applications where there is no walking surface below the glass, or where the walking surface below is permanently protected from the risk of falling glass. Maximum stresses for heat-strengthened and fully tempered glass are now provided for the design of glass handrails and guards, clarifying a previously confusing design requirement.

2407.1.1 Loads. Glass handrails and guards and their support systems shall be designed to withstand the loads specified in Section 1607.9. Calculated stresses in glass elements of handrails and guards due to these loads shall be limited to a maximum of 3,000 psi (20.7 MPa) for heat-strengthened glass and 6,000 psi (41.4 MPa) for fully tempered glass. Glass handrails and guards shall be designed using a factor of safety of four.

Change Significance: Previously, glass handrails and guards and their supporting systems (Figure 1) were required to be designed to withstand the loads as specified in Section 1607.9 utilizing a safety factor of four. An often-asked question was how to apply the safety factor of four. This modification guides those designing glass handrails or guards by providing maximum stresses for heat-strengthened and fully tempered glass that meet the previously prescribed safety factor.

Maximum stress-carrying capabilities of the two types of glass that may be used in the design of glass handrails and guards – heat-strengthened glazing and fully tempered glazing – are published by the glass industry. Heat-strengthened glass can bear stresses of 12,000 psi while fully tempered glass can bear stresses of 24,000 psi. Accordingly, the values now prescribed in Section 2407.1.1 are one-fourth of those maximum stresses. Values of 3,000 psi for heat-strengthened glass and 6,000 psi for fully tempered glass must equal or exceed the calculated stresses for the loads specified in Section 1607.9.

IBC Section 1607.9.1.1 requires that handrails and guards be designed to resist a concentrated load of 200 pounds per Section 4.5.1 of ASCE 7. Further, Section 4.5.1.1 of ASCE 7 indicates that handrail and guard systems shall also be designed to resist a load of 50 pounds per linear foot applied in any direction along the handrail or top rail and transfer this load through the supports to the structure. This load need not be assumed to act concurrently with the 200-pound concentrated load. IBC Section 1607.9.1.2 specifies that guard components including panel fillers and guard infill components are to be designed to resist a concentrated load of 50 pounds per Section 4.5.1.2 of ASCE 7. According to ASCE 7, this concentrated load is to be applied over an area not to exceed 12 inches by 12 inches.

Multipane Glazed Assemblies

In areas where it is likely that persons will impact glass or other glazing, the IBC mandates that specific glazing materials be installed. These areas, identified in Section 2406.4, are considered by the code as “hazardous locations.” Unless exempted, all glazing located in hazardous locations must pass the test requirements established in Section 2406.2 for impact-resistance. Due to some confusion as to the requirements for glazed assemblies with multiple glass panes, it has been clarified that every pane in such multipane glass assemblies be safety glazing where located in the hazardous locations identified by the IBC (Figure 2).

2406.1 Human impact loads. All glass in Individual glazed areas, including glass mirrors, single panes of glass, laminated glass and all panes in multipane glass assemblies in hazardous locations as defined in Section 2406.4 shall comply with Sections 2406.1.1 through 2406.1.4.

Exception: Mirrors and other glass panels mounted or hung on a surface that provides a continuous backing support.

Change Significance: The IBC has always mandated safety glazing for all panes of glass in a multipane assembly. However, there have been reports of such assemblies where the center pane(s) are non-complying annealed glass surrounded by panes that qualify as safety glazing. The revised code text should help ensure that multipane assemblies installed in hazardous locations are fully safe in the event of human impact and that potentially dangerous annealed panes of glass are not intermingled with safety glazing in multipane assemblies.

Glazing in Windows

IBC Commentary Section 2406.4.3 indicates that the purpose of safety glazing is to “…provide protection where the glazed opening could be mistaken for a passageway or clear opening that someone might be able to walk through, fall into, or otherwise be accidentally forced into.” For areas that meet all four criteria listed in Section 2406.4.3, safety glazing is required in a window (Figure 3). The provision also provides exceptions for 1) decorative glass, 2) protection by a horizontal rail and 3) outside panes of insulating glass units (IGU) or multiple layers of glazing.

2406.4.3 Glazing in windows. Glazing in an individual fixed or operable panel that meets all of the following conditions shall be considered to be a hazardous location:

• The exposed area of an individual pane is greater than 9 square feet (0.84 m2).
• The bottom edge of the glazing is less than 18 inches (457 mm) above the floor or adjacent walking surface.
• The top edge of the glazing is greater than 36 inches (914 mm) above the floor or adjacent walking surface.
• One or more walking surface(s) are within 36 inches (914 mm), measured horizontally and in a straight line, of the plane of the glazing.

Exceptions:

• Decorative glazing.
• Where a horizontal rail is installed on the accessible side(s) of the glazing 34 to 38 inches (864 to 965 mm) above the walking surface. The rail shall be capable of withstanding a horizontal load of 50 pounds per linear foot (730 N/m) without contacting the glass and be not less than 1.5 inches (38 mm) in cross-sectional height.
• Outboard panes in insulating glass units or multiple glazing where the bottom exposed edge of the glass is 8 feet (2438 mm) 25 feet (7620 mm) or more above any grade or , roof, walking surface or other horizontal or sloped (within 45 degrees of horizontal) (0.79 rad) surface adjacent to the glass exterior.

Change Significance: Exception 3 was sometimes misinterpreted as triggering the need for safety glazing on the exterior envelope of the building. While not the intent, ground-floor, second-floor, and even third-floor exterior windows up to 25 feet above grade were occasionally being specified or replaced with safety glazing on the outboard panes. It is inconsistent to have more stringent provisions requiring safety glazing on the exterior surfaces of the building (previously up to 25 feet above a roof or walking surface) than on the building’s interior (required where the glass is less than 18 inches above the walking surface). It is also not consistent to require safety glazing on the building’s exterior when the window is an IGU but not when the glass is single-pane.

This change makes the requirement impartial regarding the concern of falling out of a building, falling into a building, or falling through a window that does not result in a person entering or leaving a building (e.g., an interior window with floor walking surfaces on both sides). It recognizes the need to prevent situations where people on the building’s exterior (whether on a roof or adjacent walking surface) could fall through a window into a building. While this is a less likely occurrence than people falling through windows out of a building, it is a concern where windows are located adjacent to the roof level (for example a clerestory). Where the vertical distance from the bottom exposed edge of the glass to grade or to a walking surface adjacent to the window exterior is less than 8 feet, safety glazing is required on the outboard pane of insulating glass units or multiple layer glazing.

This provision would also apply along a walkway or deck that may be higher than the immediately adjacent walking surface on the other side of the window. However, because the provision had not previously considered the distance to the bottom of the window, it now addresses the concern of people potentially falling into another portion of a building regardless of whether the walking surfaces on either side of the window are at the same elevation. For example, in Figure 3, if a corridor is adjacent to an atrium and there are multiple layers of glazing, only the pane adjacent to the corridor requires safety glazing. The pane adjacent to the atrium is higher than the 8-foot threshold and would not require safety glazing.

Conclusion

Structural engineers should be aware of significant structural changes in the 2024 IBC Chapter 24 on glass and glazing. Maximum stresses for heat-strengthened and fully tempered glass are now provided for the design of glass handrails or guards. It has also been clarified that every pane in multipane glass assemblies be safety glazing where located in the hazardous locations identified by the IBC. Finally, window safety glazing is required where a person could fall through a window—either out of a building or inside the building—or into the building through a window. However, safety glazing is not required on outboard panes of glazing when the height above grade or the walking surface exceeds 8 feet. ■