Insulated glass units (IGU’s) or double glazed units are a significantly more energy efficient glazing system than single glazed windows. It is estimated that up to 30% of heat entering the home and up to 50% of winter heat loss is a result from the use of single glazing.
IGU consists of two or more panels of glass separated by airspace and aluminium or other type of spacer around the edges, sealed to the perimeter in controlled conditions. The spacer contains a desiccant (drying agent) which eliminates moisture vapour in the cavity. The combination of the two panels of glass and the trapped air is what makes IGU a superior energy efficient method of glazing.
The glazing system must be designed to drain out all water in the rebate and a void must exist under the unit so that moisture is not trapped against the edge of the glass.
Generally units should be glazed with a minimum 3mm clearance between the glass face to rebate a minimum 3 - 6mm clearance under the unit in the rebate (size of block) and a minimum 12mm cover or bite in the rebate.
Dry glazing of units is always recommended but if units are to be glazed or bedded into compounds or sealants it is imperative that compatible sealants are used or edge failure may result.