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Insulating Glass
In order to reduce heat gain or loss through glass, two or more lites may be sealed together to create an insulating glass (IG) unit.

The majority of insulating glass units consist of two lites of glass enclosing a hermetically sealed air space. The lites are held apart by a spacer around the entire perimeter. The spacer contains a moisture-adsorbent material called desiccant that serves to keep the enclosed air free of visible moisture. The entire perimeter of the assembly is sealed.

The most commonly used edge construction contains a metallic spacer of roll-formed aluminum, stainless steel, coated steel or galvanized steel. It is sealed with a single seal of polysulfide, polyurethane or hot-melt butyl, or with a dual seal consisting of a primary seal of polyisobutylene and a secondary seal of silicone, polysulfide or polyurethane. The corners of the metallic spacer may be square-cut and joined with a metal, plastic or nylon corner key, may be miter-cut and brazed, welded or soldered, or may be bent. Recent years have seen the introduction of warm edge technology products as spacer materials. These products include extruded butyl materials, foam rubber based materials, formed plastics and metal strip based products, many with desiccant included as a component.

Improvements in edge of insulating glass U-values as a result of warm-edge technologies play a vital role in meeting overall window performance requirements for state adopted residential fenestration codes.

Thermal performance of insulating glass units is enhanced by using solar control substrates and coated glass (low-emissivity or reflective), coated polyester suspended films, insulating gases (such as argon, krypton or xenon) and warm edge technology products. Initial heating and cooling equipment costs and ongoing operating costs are reduced.

Insulating glass units also offer benefits by reducing sound transmission. Laminated glass constructions and sulfur hexafluoride (SF6) gas filling further enhance the sound reduction characteristics of the insulating glass unit.

Industry product classification, performance requirements and testing procedures for insulating glass units are defined in the following ASTM International documents:

E 773 Standard Test Method Accelerated Weathering of Sealed Insulating Glass Units
E 774 Standard Specification for Sealed Insulating Glass Units
E 2188 Standard Test Method for Insulating Glass Unit Performance
E 2189 Standard Test Method for Testing Resistance to Fogging in Insulating Glass Units
E 2190 Standard Specification for Insulating Glass Unit Performance and Evaluation

Most insulating glass fabricators voluntarily participate in insulating glass certification programs. The purpose of the certification programs is to assure the user that the purchased product is a faithful replica of one that has passed certain prescribed tests. Therefore, participants in a certification program must complete the following requirements: 1) submit specimens of their production product to independent testing laboratories for the prescribed tests; and 2) agree to periodic, unannounced inspections of their regular production by an independent agency to ensure that actual production employs the same materials and techniques as the tested specimen.

The Insulating Division of the Glass Association of North America (GANA) and the Insulating Glass Manufacturers Alliance (IGMA) promote the highest standards in insulating glass unit production, testing, certification and business ethics through their memberships. The industry establishes voluntary quality standards and collects statistical and other non-proprietary information related to field performance of insulating glass for dissemination to manufacturers and consumers.

Note: The GANA Glazing Manual (Section II - Fabricated Architectural Glass Products) should be consulted for additional detailed information on insulating glass design considerations, material compatibility and glazing guidelines prior to specifying and using insulating glass constructions.

The above information is from the GANA Glazing Manual, 2004 Edition - the most frequently referenced resource in the architectural glass and glazing industry. The Glazing Manual is an excellent addition to any technical library. Go here to order a copy of the manual or CD-ROM. For further information on this and other GANA reference documents visit the PUBLICATIONS section of the GANA website.

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Last modified: 11/09/08