Laminated Glass and the 2015 International Building Code
Glass looks great, but needs to be safe.
Glass has long been prized as an architectural element for railing and guard systems to enhance the appearance of shopping malls, arenas, museums, condos and many other types of buildings – while also providing safety for occupants and visitors. Glass not only looks very clean and minimalist, it allows the greatest line of sight from many different vantage points.
Unfortunately, in recent years, several high profile incidents of glass breakage, which resulted in glass fallout, have sparked concern over the safety of glass railings and guard systems. If the elements designed to protect people are actually potentially harming them, then there is definitely a problem.
In order to address the issue of glass breakage, the 2015 International Building Code (IBC) calls for the use of laminated glass in most railing applications. This represents a major change to the monolithic glazed glass that is currently used for most railing and guard systems.
By requiring heat strengthened or tempered laminated glass in railing systems, the 2015 IBC model code has taken a major step forward in terms of improved safety. On the other hand, this change represents a major adjustment for owners, designers, architects and general contractors, as you consider current or future renovations and new development.
From monolithic to laminated glass – the new code is here.
Driven by safety concerns and improved production techniques, laminated glass has been used in guardrail systems in Europe for years. Now, several U.S.-based fabricators have adopted similar production processes, and more and more states and local jurisdictions in the U.S. have adopted and are enforcing IBC 2015 building code. See where your state is on the adoption curve.
What exactly is the new code?
The revised model code (Section 2407.1) now states, “handrail, guardrail, or a guard section shall be laminated glass constructed of fully tempered or heat strengthened glass and shall comply with Category II or CPSC 16 CFR Part 1201 or Class A of ANSI Z97.1. Glazing in railing in-fill panels shall be of an approved safety glazing material that conforms to the provisions of Section 2406.1.1. For all glazing types, the minimum nominal thickness must be 1/4 inch (6.4 mm).”
Section 2403.4 states “where interior glazing is installed adjacent to a walking surface, the differential deflection of two adjacent unsupported edges shall not be greater than the thickness of the panels when a force of 50 pounds per linear foot (plf) (730 N/m) is applied horizontally to one panel at any point up to 42 inches (1067 mm) above the walking surface.”
Section 2403.4 was added to mitigate against “pinching hazard” which can occur in interior applications when an individual may contact the glass panels (inadvertently or otherwise) with an impact force that exceeds the differential deflection minimum. Mullions prevent this from happening in exterior applications.
There are exceptions noted in the model code that permit monolithic tempered glass in railing systems:
• For applications (such as on ground floor) based on the absence of a walking surface beneath the railing or the permanent protection of the
walking surface from the risk of falling glass.
• Infill panels that do not support the railing (such as in post mounted systems) also have less stringent requirements and may be satisfactory
to the local jurisdiction with tempered monolithic glass.
The transparent truth: Why a new code now?
Historically, tempered glass typically has been specified over laminated glass for two reasons, lower cost and aesthetics, as many designers do not
want to have an “unsightly” laminated edge showing. However, after a number of highly publicized incidents involving window and balcony glass breaking spontaneously and falling from high-rise buildings, the Glazing Industry Code Committee (GICC) proposed the changes.
It doesn’t take an earthquake or violent impact for tempered glass to break. On a day-to-day basis glass railings are exposed to potential incidents that could cause breakage, such as strollers, delivery carts, or even workers unintentionally bumping into them with floor cleaning machines. However, the most common causes for breakage are not related to impact. The most common causes are:
• Poor edge quality: The most common is damage to the edges of glass as it is being pre-cut into panels, or nicks or chips to the edges that
occur when the glass is being packaged, shipped, or installed onsite.
• Frame-related breakage: Expansion and contraction of glass framing members may also lead to frame-related breakage
• Thermal stress: Thermally induced stresses in glass are caused by a positive temperature difference between the center and edge of the glass lite, meaning the former is hotter than the latter.
• Nickel-sulfide inclusions: Small nickel-sulfide stones can form randomly in the production of float glass.
Most North American glass makers have controls that greatly reduce the likelihood of nickel sulfide formation. However, glass coming from other parts of the world may have less controls in place, and although this glass can be attractive due to pricing, users can end up seeing that savings are lost when liability issues arise. In addition, North American glass manufacturers do not use nickel in batch formulations for primary glass and go to great lengths to avoid nickel-bearing components in their glass-melting processes. Despite rigorous quality controls and procedures aimed at reducing the likelihood of nickel-sulfide stones, there is no technology to completely eliminate their formation in today’s float glass.
Factor in litigation and liability costs
As a result of these accidents, a number of class actions lawsuits have been filed around the country as a result of shattered glass panels. For example, as reported by US Glass Magazine, “The plaintiffs are alleging breach of contract by the developers of the three properties because of the time they were barred from their balconies following the displaced glass panels that fell from their homes onto the streets below, as well as diminished property values as a result of the highly publicized incidents.”
Bernard Lax puts this in perspective. “In the past many developers see the line item costing of the laminated glass selection versus monolithic glass and balk at the idea of its use. When you factor in the litigation and liability costs associated with the multitude of legal actions the delta of the selection of laminated glass can seem like a bargain.”
Laminated glass: A quick overview
Laminated glass features two pieces of glass “sandwiching” a plastic interlayer, which provides an added level of safety. If breakage does occur, the glass does not typically fall away, as it is held in place by the plastic interlayer. With durability requirements in building applications increasing over the past two decades, the composition of the interlayers has been improving to meet these requirements. Today there are different types available, with basically two families of structural interlayers to choose from:
• Ionoplast interlayers (such as SentryGlas® Interlayer)
• Stiff Polyvinyl Butyral PVB (low plasticizer)
These interlayers feature a much higher shear and elastic modulus than tempered glass, increasing the strength of the laminate and enhancing the
coupling between the glass panes. Stress and deflection are reduced, which will allow the use of lower laminated glass thickness and/or increased glass spans.
The extra stiffness of the interlayer also enhances post breakage performance, and is particularly well suited for structural applications such as:
• Minimally supported glass construction
• Overhead glazing
• Structural balustrade systems
Standard PVB interlayer (originally developed for windshield glass shard retention and later on impact performance) is still used in special glazing applications but is getting increasingly replaced by higher performance structural interlayers. (i.e. SentryGlas®) With the different types of interlayers, there are differences in performance, especially with regard to the sensitivity to develop defects at the edges. Interlayer suppliers should be consulted to understand these differences and select the right interlayer for the specific application.
Three key insights for meeting the laminated glass code
1. It’s going to cost more. Changing from tempered glass to laminated glass increases overall guardrail cost by 20-30%.
The complexity of the lamination process and extra materials naturally means that laminated glass is going to cost more than standard tempered glass. Understanding that there is a significant cost differential will help you prepare ahead of time for increasing budgets or cutting costs in other areas to offset the increase.
While the increased cost cannot be avoided, you can reduce the risk of budget overruns by understanding the differences between laminated glass and tempered glass and how the code change will affect the design and renovation process.
In addition, working with a specialist who provides design input and warranties on materials and workmanship helps you ensure quality. One who has industry experience designing and installing railings and guards using the laminated glass will help ensure that you do not spend more than is necessary.
2. It’s going to take longer to get the glass. Laminated glass can take up to 50% longer to fabricate.
The additional steps needed to manufacture laminated glass are complicated and increase the lead time. So plan accordingly.
Different vendors design to different specifications. And the durability of laminated glass will depend of a number of design and manufacturing factors.
Some things to discuss with your vendor:
• Quality of the lamination process.
• Quality of the glass.
• Edge quality (alignment and smoothness)
• Procedure and quality of the glass installation.
• Glass fixation system.
• Interlayer selection: Type and thickness.
3. The laminated glass will affect your design. Make sure you understand how.
It’s important to understand the exposure of the glass edges to moisture, temperature, and sealants, and how those factors might degrade performance over time.
Edge Conditions
Edge quality is of paramount importance for structural integrity as well as appearance. The standard tolerance for laminated glass edge mismatch according to ASTM C1172, Section 8.5.1 can be up to ¼ inch. A mismatch of this magnitude may, however, create issues with the performance of the glass, particularly when a load on the edge is concentrated on one lite. The exposed edge is easier to bump into and is the weakest link when it comes to breakage.
To add in a higher degree of safety, designers can specify tighter tolerances, per ASTM C1172, Section 8.5.3, but it will increase the cost. Treatments such as top channels/caps can also be used to mask any deficiencies in the edge matching. Though some designers resist this option, a continuous top channel eliminates the need for a handrail as the top channel doubles as a structural element.
Moisture, Environmental Exposure and Laminate Erosion With laminated glass, it is important to consider compatibility of the glass and interlayer with any sealant, grout or cement that may come in contact with the glass and interlayer. Since the interlayer will come in contact with the other components ( such as water), it is critical to make sure they are compatible chemically and that no interaction will occur with long-term contact. In general, epoxy or polyurethane based grouts have superior performance characteristics compared to Portland based cement, which is highly alkaline and may attack the laminate structure. In shoe mounted or cantilevered systems, this delamination occurs below the line of sight so it may be difficult to detect until the glass has been seriously weakened.
Ionoplast interlayers tend to stand up to the elements (or frequent glass washing on interior applications) better than standard PVB. Ionoplast interlayers will have better structural properties than stiff PVB interlayers at temperatures above 30C (86F)
With post mounted systems there is no chance of interaction with grout, since instead of a glass panel being captured at bottom, it is bolted to the post. However, those bolt holes weaken the laminate, creating stress and potential for de-lamination at those points, unless a structural interlayer (ionoplast or stiff PVB) is used.
Summary
Yes, it’s going to cost more money and require you to adjust your designs and timelines. So make sure to consult with industry experts and retain glass railing specialists who are knowledgeable and reputable when it comes to making recommendations that follow the new code. The key is to be knowledgeable of the changes and to partner with industry experts to mitigate the exposure and potential risks to the owners, designers, architects
and general contractors as you consider current or future renovations and developments.
Sources:
constructionspecifier.com “Spontaneous glass breakage. Why it happens and what to do about it” 10/11
architectmagazine.com “Falling Glass Closes New W Hotel in Austin, Texas” 09/11
Bernard Lax CEO of Pulp Studio
GANA Perspectives “ Guiding the Rails”, Mark Jacobson 09/15
Glass Performance Days 201 Tampere, Finland. “Which interlayer for which glazing application?“
Björn Sandén Kuraray Europe GmbH 06/15
USGlass, Metal & Glazing “Tale of Three Cities – and lots of broken glass” 10/11
