Secondary glazing, often referred to as secondary double glazing and secondary windows, is an added glazing layer fixed within a window opening in its own frame. It can be described as an independent glazing system. The size of space between the two glazing layers determines the amount of insulation. A larger space provides greater insulation than a smaller space. In this way, heat loss is reduced and soundproofing is increased. Low ‘E’ glass can be used to improve on the insulating quality of replacement sealed unit double glazing. This meets the requirements of the improved energy rating in the new Energy Performance Certificate for the Home Buyers Pack. By using specialist glass external noise reduction from aircraft, road traffic and railway traffic can be further reduced. When secondary glazing has been installed you will notice a reduction in your heating bills. Approximately 20% of domestic heat loss is through single glazed windows. By fitting double glazing, including secondary glazing, heat loss can be halved. The principle of secondary glazing is similar to that of double glazing, although some double glazing units consist of two glazing panels with a gas filled gap between them.
The cost of secondary glazing is significantly lower than that of replacement double glazing. In addition, it enhances security as it can only be opened from inside a property. Additional locks can be fitted and toughened or laminated glass used. Because secondary glazing reduces air movement the amount of dust infiltrating a room is greatly reduced. Specialist glazing can be used to filter out much of the sun’s harmful rays in order to protect furnishings and carpets.
The external character of a property is retained when fitting secondary glazing, a fact that is particularly relevant in relation to historic buildings, conservation area properties and listed buildings. Secondary glazing is available in a choice of materials such as hardwood, uPVC or aluminium for example, and a variety of colours. It is usually fitted as a single glaze unit although double glaze units are also available. Glass panes are secured by compression gaskets within an extruded framing section, which is in turn mounted via rollers, hinges, spiral balances or glides onto an outer frame. This enables the individual panel or glass pane to slide or open up or across, in order to access the primary window for ventilation purposes. This does not apply to the lift out model and fixed unit,however, which can be lifted in and out or are permanently fixed. Where secondary glazing is fitted there is no need to seal up or draught exclude the original glazing panel.
A great deal of thought goes into designing secondary glazing in order to make it as discrete and unobtrusive as possible. Secondary glazing units can also be applied to doors and are particularly beneficial when fixed to existing French or patio doors. The benefits of fitting secondary glazing include:-
- Thermal insulation,
- Reduced heating bills,
- Noise reduction,
- Easy maintenance and cleaning,
- Easy access to primary glazing panel,
- No painting needed on uPVC or aluminium frames.