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Insulating Issues: May-June-2010

Analysis bolsters independent, third-party certification

June 11, 2010  By Margaret Webb

Insulating Glass units are unique in the realm of manufactured products

Insulating Glass units are unique in the realm of manufactured products. The IGMA 25-Year Field Correlation Study established baseline and ongoing quantitative statistics on long-term performance.

IG units are a large product with a hermetic seal and are installed in harsh environments subject to ultraviolet rays, water, extreme temperature changes and even oscillating loads. IG units can also be exposed to organic adhesive materials and are often fixed in place by an unknown framing material. Comparisons can be difficult as these units are commonly installed in different conditions.

IGMA 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. Initiated in 1980 by IGMA (then the Sealed Insulating Glass Manufacturers Association) and the U.S. Department of HUD, the results of the 25-year study definitively demonstrate that third-party certification is critical in establishing the integrity of these products.


This study was an ambitious project that examined in-service insulating glass units in specific residential and commercial buildings in various locations across the United States and correlated appropriate test measures as well. It was begun in 1980 with reports issued at the 10, 15 and finally, 25-year marks. And although there were extensive management changes in terms of the sponsors of the research, IGMA continued its pledge over the years, with the goal to accumulate results at the quarter-century mark.

The results are noteworthy in that the overall failure rates of IG units are low, despite a wide geographic range of surveyed buildings, a wide range of different field units and a wide range of environmental conditions. 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 per cent 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 per cent of the failures that did occur in the remaining buildings.

The Field Correlation Study provides insights into improving the glazing systems utilized, manufacturing techniques as well as overall performance criteria of insulating glass. The study included 140 buildings in 40 cities containing a total of 40,000 certified IG units of which two-thirds were field-glazed commercial units and one-third were residential windows. Of this total sample, the field failure rates of 2,400 IG units in 140 buildings in 14 cities were studied in detail. The second study examined more than 14,000 units that incorporated newer technologies and that demonstrated a failure rate of one percent at the 15-year mark.

Based on the information obtained from the 25-year data, it is estimated that the failure rate of units tested to less stringent levels is in excess of 20 per cent, due to the number of buildings re-glazed and known systems that were not properly performing to keep water away from the insulating glass edge. In addition, the number of these units demonstrating failure in the 25-year study (14 per cent) was approximately three to four times the number of failures of those tested and certified to the highest level.

IGMA encourages the industry to adhere to best practices, to meet the highest level possible certification and to employ industry standards such as TM-4000-90-(04), IGMA North American Glazing Guidelines for Sealed Insulating Glass Units for Commercial and Residential Use. 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 insulating glass unit will result in premature failure, will cause structural damage to the glazing system and may result in the formation of mould. The formation of mould and its effect on the occupants of a structure continues to be a prime health and safety concern for architects when designing buildings.

When a customer asks “why should I buy certified insulating glass units?” manufacturers can refer to the IGMA 25-Year Field Correlation Study for proven field performance.

For additional information on the study or other publications, please contact IGMA at 613-233-1510.

Margaret Webb is the executive director of the Insulating Glass Manufacturers Association (IGMA). She can be reached at

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