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Passing the Test
The Power of Certified and Tested Units: 25 Years of Proof
by Margaret Webb


The Insulating Glass Manufacturers Alliance (IGMA) 25-Year Field Correlation Study brings real-world performance and results to further establish a case for quality, tested and certified insulating glass (IG) units. Third-party certification of IG units is critical in establishing the integrity of these products.

The purpose of the 25-year field correlation study was to determine the correlation of actual in-service IG unit failures to the ASTM E 773 Standard Test Method for Accelerated Weathering of Sealed Insulating Glass Units and ASTM E 774 Standard Specification for the Classification of the Durability of Sealed Insulating Glass Units for classes C, minimum performance; CB, moderate/mid-level performance; and CBA, maximum performance (see box 1 on page 78 for more details; Editor’s note: both ASTM E 773 and ASTM E 773 are now obsolete. The replacement document is ASTM E 2190 Standard Specification for Insulating Glass Unit Performance and Evaluation).

Background
The IGMA 25-year field correlation study established baseline and ongoing quantitative statistics on long-term performance.

IGMA now has the quantitative results that prove sealed IG units tested and certified to the most stringent industry standards carry better in-the-field performance than those that are not. The study was an ambitious project that examined in-service IG units in specific residential and commercial buildings in various locations across the United States. The project began in 1980 with reports issued at the 10-, 15- and finally, 25-year marks. The study was based on long-term analysis of in-the-field building performance and examined in-service insulating glass units in specific residential and commercial buildings located in all regions of the United States. Almost all the units studied faced south or southwest.

The standard for visual failure was defined as “moisture, fog or dirt collection on the glass lite surfaces located within the air space,” exhibiting “permanent material obstruction of vision through the unit due to accumulation of dust, moisture or film on the internal surface of the glass.” In the first seven years, frost points were taken on almost all the units. Visual inspections were completed eight times during the first ten years and again at the 15- and 25-year point.

In 1990 an additional study was undertaken to examine more than 10,000 CBA units in 102 buildings from units. This part of the study was designed to include some of the newer seal and edge technologies that were added since the original study.

The Results
Although applications were wide ranging, actual performance varied little from hot to cold or wet to dry climates or sea level to mountain exposures. Eighty percent of the buildings had no insulating glass failures after 25 years. Glazing systems that held water at or near the edge sealant had accelerated 60 percent of the failures that did occur in the remaining buildings. The importance of managing water in the glazing cavity is a critical factor in the performance and longevity of certified insulating glass units. Water held at or near the edge seal of an IG unit will result in premature failure, cause structural damage to the glazing system and may result in the formation of mold (see box 2 at left for more information on the study’s results). The formation of mold and its effect on the occupants of a structure continues to be a prime health and safety concern for architects when designing buildings.

Based on the information obtained from the 25-year data, it is estimated that the failure rate of C and CB units is in excess of 20 percent, due to the number of buildings re-glazed and known systems that were not properly performing to keep water away from the IG edge. In addition, the number of C and CB units demonstrating failure in the 25-year study (14 percent) had approximately three to four times the number of failures of the CBA units (3.6 percent). This clearly demonstrates that the units that achieved the CBA or highest level of certification outperformed the units that had only achieved the C or CB level of certification.


Margaret Webb, CHRP, is the executive director of the Insulating Glass Manufacturers Alliance in Ottawa, Ontario. Additional information about the organization can be found online at www.igmaonline.org.

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