IGU (insulated glass unit)
An IGU (insulated glass unit) is a sealed double-glazed assembly used in windows and doors. Failed IGU seals cause fogging between panes.
Ask Chalkline about this →An IGU (insulated glass unit) is a factory-sealed assembly of two or more glass panes separated by a spacer bar and hermetically sealed at the edges to trap a layer of air or inert gas (typically argon) in the cavity. The sealed cavity improves thermal insulation and reduces condensation on interior glass surfaces compared with single-pane glazing. IGUs must comply with AS/NZS 4666:2012, which sets requirements for construction, materials, and performance of insulating glass units in Australia and New Zealand.
The most common post-occupation glazing defect is IGU seal failure: when the primary seal is breached, moisture enters the cavity and the desiccant inside the spacer bar becomes saturated. The result is visible fogging or condensation between the panes that cannot be wiped away. Failed IGUs must be replaced as a unit; field repair is not possible. Causes include edge damage during installation, incompatible sealants, and manufacturing defects.
Also known as: insulated glass unit, double glazing, sealed unit
Category: Glass types and systems
Related
- Glazier (trade), the trade that installs and replaces IGUs on residential jobs
See also
- Toughened glass (glossary), the most common glass type used in IGU assemblies
- Laminated glass (glossary), used in IGUs where overhead or barrier applications require it
- AS 1288:2021 glass in buildings (regulation), which covers installation of glazed assemblies including IGUs
Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.