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
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).
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.
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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