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’s consist 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’s 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.
It is estimated that in an uninsulated home up to 30% of heat entry can be attributed to clear single glazing. In these situations single clear glazing is recommended only for shaded windows, where glare is not a concern or where maximum natural daylight is required.
DOUBLE GLAZING or IGU
Double glazing or insulated glass units (IGU) have better insulating qualities than single glazing. When using the U-value performance indicator which measures the amount of heat transfer, IGU’s decrease this rate of heat transfer by up to 50%. This means a cooler or warmer environment with lower energy costs.
Water from condensation build-up and resultant water run-off can damage window frames/sills and seep into walls and adjoining areas. Condensation will form when the moisture in the air condenses out on surfaces that are cooler than the ‘dew’ point. Insulated walls, ceilings and floors provide better thermal barriers than windows. Window surfaces being colder than other surfaces in the home or building are more prone to condensation build up. An IGU reduces the likelihood of condensation forming by providing a thermal barrier between the inside and the outside.
The use of solar control glass (tinted floats or reflectives) may affect the thermal safety of the glazing unit. Careful consideration needs to be given to building design, frame type, glazing methods, proximity of blinds, screens or curtains and external shading. Refer Thermal Breakage.