Over the years, there has been confusion on whether a top railing was required in glass railings. In my opinion, it was required. In 2009, the International Building Code (IBC) in 2009, which allowed for an exception. The exception? There was no top rail requirement when using laminated, tempered or heat-strengthened glass.
But, since 2015, the IBC now has required laminated, tempered or heat strengthened glass in all glass railings. If that’s the case, why bother having a top rail?
There are still issues to consider.
1. Not all laminated glass is equal.
Let’s consider how different types of laminated glass perform.
In this video, the first impact is on monolithic tempered glass. The glass shatters completely leaving an opening which would remain a risk to others.
The second test features tempered glass with a polyvinyl butyral (PVB) interlayer. PVB interlayers were developed for the auto industry for use in windshields. When there is a possibility of human impact, laminated glass offers a level of safety not possible with monolithic glass.
If one or both of the glass plies are thick enough to resist breakage, the glass will remain in place. But, if both glass plies break, the glass will drop like a wet blanket. The guard now has a void which would result in a continuing risk.
The third test is tempered glass with an ionoplast, rigid interlayer. With an ionoplast interlayer, if both glass plies break, the interlayer remains rigid. The glass stays in place mitigating the hazard for other others.
2. Edge alignment of laminated glass
Customers and designers are still looking for the finished edge that they were able to get with monolithic glass. But this is not easy when laminating glass. This demand has pushed the industry to develop guidelines for laminated edge conditions. But currently, no such guidelines exist.
With exposed edges of laminated glass, the alignment of glass plies is critical to the designer. Covering the top of the glass with a top rail, will remove this concern.
It is important to let customers know that laminated glass, when viewed from the edge, has a layered appearance. It will not look like monolithic glass.
Exposed glass edges are polished before heat-treating. With monolithic glass, the polished edge will not look any different after heat treating. When assembled into a laminate, alignment issues may arise. The edges may not align to an acceptable condition after the laminating process. With laminated glass, it’s up to the glass fabricator to reduce mismatch and trim the interlayer material.
The industry currently has no generally accepted exposed-edge tolerances to offer as guidelines beyond what appears in ASTM C1036, C1048, and C1172. Consult your glass supplier when ordering your glass. You may decide to order laminated glass with tighter tolerance than those provided in the ASTM C1172 standard.
In certain conditions, laminates may absorb contaminants that will result in delamination. Generally, this is not an issue for interior applications. But should be a concern for external applications.
In wet-glaze glass railing applications, the choice of grout for setting the glass in the base molding may present issues. Any wet-glaze setting medium that is not impermeable to water may result in delamination.
But, this is not just an issue with wet-glaze glass railing. laminates have the potential to absorb contaminants in their environment. Using a top rail reduces the risk of contaminant absorption through the top of laminated glass.
Dry-glaze glass railing systems (such as Wagner’s PanelGrip) have become a significant percentage of the market.
One of the challenges of dry-glaze glass railings is assuring vertical alignment of the glass lites. Even when properly installed, the top line of the glass lites, may not align. A top rail will correct this. There is enough flex in the glass that a top rail will align the glass panels.