The following information is provided by Cardinal Glass Industries Comapny as a Technical Service Bulletin. To view the original bulletin, click here.
“When internal dividers are used in an insulating glass unit, such as grilles, muntin bars, or simulated divided lites, there is the potential that dividers will contact the airspace glass surfaces (surface #2 and #3) of the insulating glass unit. This can occur under the following conditions:
When the insulating glass unit airspace pressure is below the atmospheric pressure (IG unit is concave).
This is caused by:
Cold temperature conditions
High barometric pressure conditions
The Insulated glass unites or windows are being shipped to an altitude below the insulated glass fabrication altitude
Fabrication of insulating glass units where the insulated glass unit airspace thickness tolerance is at a lower limit
Buffeting wind conditions
Fabrication of tempered insulting glass units where the tempered glass has a bow in the glass
When the metal dividers contact the airspace glass surfaces, there is the potential for having condensation on the room side (#4 glass surface) immediately behind the metal divider. This is because the insulating glass unit has lost its insulating value where the divider contacts the glass surfaces, causing the indoor glass surface to be colder. Therefore, there is more opportunity to have room side condensation with internal grilles than with standard insulating glass products that do not contain these grilles.
In addition, with large glass units utilizing long spans of the internal metal grilles, there is a chance for brief glass-to-internal grille contact. Swinging or sliding patio doors that are rapidly swung open or shut could result in the grille contacting the glass resulting in a brief rattling noise. This brief rattling noise is not a product defect and does not warrant replacement of the glass.
The National Fenestration Rating Council’s Procedure for Determining Fenstration Product U-factiors (NFRC 100: 2001) states:
“Products with glazing dividers between lites of insulating glass may be assumed to have the same U-factors as identical products without such dividers, providing there is at least 3.00 mm (0.118 in.) air/glass space between the divider and both glass surfaces.”
The information in this Technical Service Bulletin is subject to disclaimers and other limitation appearing in the DISCLAIMER at www.cardinalcorp.com.”