Why is Laminated Glass Required for Glass Railing?
Laminated Glass Code Requirements
Since 2015, the International Code Council (ICC) has required that all glass used in glass railings be laminated, heat-strengthened or tempered glass.
You may wonder, “how did this come about?”
Here’s a little history.
Prior to 2015, the requirements for glass in glass railing were for tempered or heat-strengthened glass. If no top rail were desired, an exception was noted waiving a top rail requirement if laminated glass was used.
But, there were several significant glass railing failures throughout North America several years ago. US Glass Magazine wrote a story about the failures back in October 2011. You can view the article on page 32.
The article refers to several failures in glass railing in Canada and the U.S.
The cover photo of that article was from the W Hotel in Austin, TX. In that case, a glass infill panel shattered.
Eventually, the cause of the failure was attributed to the loosening of grout from an upper floor which dislodged and struck the top edge of a tempered glass panel on a lower floor. When the panel shattered, the debris struck the top edges of other glass panels below causing them to fail as well.
The hotel was closed for 11 days and all of the glass was replaced with laminated, tempered-glass.
Soon after that failure in Austin, a high-rise in Toronto was experiencing spontaneous breakage of glass in their balcony railings.
Spontaneous Glass Breakage
Spontaneous glass breakage may occur without any obvious cause. It could be due to:
- Glass edge damage or impact
- Surface damage from handling and glazing that then weakens the glass during high winds,
building or framing system movement
- An inclusion inside the glass
There are more than 50 types of inclusions in float glass. The most widely discussed is a nickel sulfide stone.
Nickel-sulfide stones can form during the production of float glass due to contamination. It can end up in the center tension zone of tempered glass. After that glass is installed and exposed to varying temperatures, this tiny stone may grow in size and cause the glass to shatter.
Spontaneous breakage caused by nickel-sulfide inclusions occurs only in tempered glass.
There is no known technology to completely eliminate nickel-sulfide stones in float glass. And because they are so small, there is no practical way to inspect for them.
Most North American glass manufacturers have controls in place to prevent nickel-sulfide formation. Heat soaking after fabrication may destroy some flawed glass panels. But, heat soaking cannot guarantee the 100% elimination of nickel-sulfide inclusions.
Heat soak testing is a destructive test for nickel-sulfide inclusions. Tempered glass is put into a heat soak oven and brought to, and held at, a temperature of 555 degrees Fahrenheit for two hours.
Most glass containing nickel-sulfide will shatter during this process and be eliminated from the glass project. But, heat soaking cannot guarantee the 100% elimination of nickel-sulfide inclusions.
With the spate of glass failures, a code proposal was submitted to the ICC during the 2015 code cycle which would require the use of laminated tempered or laminated heat-strengthened glass in all glass railing installations. During the code hearings, the committee chose to disallow the proposal.
However, in the final meeting of the code review process, a floor vote was called. With a two-thirds majority vote, the committee decision was over-ruled. With that, the 2015 codes would require the use of laminated glass.
But, there are differences in laminated glass. This video compares the performance of monolithic tempered glass, polyvinyl butyral (PVB)laminated glass, and ionoplast laminated glass
The first test is for monolithic tempered glass. When the glass shatters, the resulting opening presents a continuing hazard.
The second test shows the effect of an impact on polyvinyl butyral (PVB) laminated glass. PVB is a spongy material. It was developed for the auto industry and its purpose is to prevent passengers from passing through the windshield in an accident. If both plies of glass break, the panel will remain intact but it will drop like a wet blanket resulting in a void. In recent years, rigid PVB layers have been developed to provide a safer alternative.
The third test is for glass with an ionoplast interlayer. Ionoplast is rigid. When both plies break in this test, the panel remains in place providing a safer end result. Learn more about ionoplast interlayers.
For more information contact Wagner.