One of the options for replacing original single Georgian glazing is provide an insulating glass unit (IGU) containing either dummy Georgian inserts or additional spacer bars to create the illusion of a multi pane panel. The effect is completed by the external application of timber or PVC-U strips placed over the internal bars externally. Unless the inserts or external bars have been specifically designed for use in an IGU there may be unforeseen problems. In particular insufficient clearance between the inner bar and glass the inserts can lead to glass breakage. Materials placed inside an IGU can give off volatiles that can condense on the inner glass surface as a chemical haze. Care should be taken to select products that have been tested for use in an IGU.

The break pattern of fractured glass when used with incorrectly designed internal inserts can be mistaken for thermal breakage. Typically, the breaks are crescent-shaped and may stop short of the glass edge. In use the glass flexes in and out with temperature and air pressure changes. An incorrect bar can act as a bending point creating excessive stress in the glass.