Taking the Edge Off: Working Together on IG Edge Pressure Efforts

By Helen Sanders

The Insulating Glass Manufacturers Alliance (IGMA) and the American Architectural Manufacturers Association (AAMA) currently are collaborating on investigating the causes and consequences of excessive edge seal pressure on insulating glass units (IGUs). Edge seal pressure is the force exerted on the perimeter seal of an IGU by a glazing system, and is applied, for example, by the wedge gaskets of a dry glazed system or the pressure plates of curtainwall.


The Goldilocks principal is at play when it comes to applying edge pres-sure on an IGU: It must be “just right.” The pressure can’t be too low, or else the system won’t be water tight. It can’t be too high either, or the edge seal will be damaged. From an installation perspective, the most immediately noticeable impact of inappropriate edge seal pressure is from insufficient pressure: water leakage. And since that’s never a good problem to have, the natural tendency is to ensure that the edge seal is really tight. However, even though the negative impacts of excess pressure on the edge are less noticeable immediately (except in the extreme of glass breakage), the results are equally problematic.

Excessive edge pressure can lead to a squeezing of PIB into the vision area, also called scalloping. This is an aesthetic issue that may be a cause for rejection. If too much pressure is exerted, the PIB can be squeezed out so much that no PIB remains between the glass and spacer, thereby permanently damaging the water and gas seal. Alternatively, the PIB can be squeezed out so thinly that it cannot effectively perform its water vapor and gas barrier function. In these scenarios, the impact can be reduced life-time of the unit due to premature seal failure.

An edge seal pressure specification of 4 to 10 pounds per linear inch has been the de-facto standard appearing in the industry’s glazing manuals since the 1970s. So why reevaluate now? In recent years, negative impacts of excessive edge seal pressure have been reported, especially in pressure plate curtainwall applications. Since these limits were first defined, the range of glazing and edge seal systems have in-creased substantially, including the use of more flexible edge seals, which may require different specifications.


A joint IGMA/AAMA task group was formed in 2015 to investigate aspects of edge pressure to understand this issue better. It’s become clear that it’s not as simple as it might seem. First, it’s difficult to measure the edge seal pressure in-situ. Reproducing the impacts of excessive edge seal pressure requires mimicking the thermal cycling seen in the real application in tandem with the edge pressure. In addition, the edge seal pressure exerted by a glazing system is also a function of the actual IGU thickness, the size and durometer of the gaskets. Also, the allow-able thickness range for an IGU is quite wide due to large tolerance stack ups, especially when using laminated glass. As a result, up to three different gasket sizes may be included in a design for a glazing system in order to accommodate all glass thicknesses within the typical range of a 1-inch nominal IGU. Not choosing the appropriate gasket size for the actual glass thickness received may result in an edge pressure that is not in the “just right” range.

This task group is planning on funding a university research group or independent laboratory to move the study forward. Anyone interested in joining the task group or responding to the request for proposals to do the research should contact Marg Webb, IGMA executive director, at mwebb@igmaonline.org.

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