Double Glazed Units

Understanding the importance of the glass used!

Double Glazed Units: Choosing the right glass

Double glazing has many positive features, depending on what type of glass is used. It is therefore important that thorough research is carried out before installation. This ensures that your new double glazing will indeed meet your needs and turn out to be a cost-effective option in the long term. Double glazing sports many benefits that has made it the standard choice for both newbuild and replacement windows market.

Construction of Double Glazed Unit

Double Glazed Unit Cross SectionDouble glazing essentially consists of two panes of glass which are 4mm thick that are sealed together. Between them there is gap of either 6mm, 8mm, 10mm 12mm, 14mm up to 20mm (which is considered the optimum gap) that is set using spacer bars between the panes. The material used for the spacer bar is incredibly important. In the past aluminium was often used as the spacer bar but the problem with this is that it is an incredibly good conductor of heat and cold meaning that cold could be transferred from the outside and heat lost from the inside. Today ‘warm edge’ bars are used to space the gap and these act as a thermal barrier.

The gap itself filled with air or an inert gas such as argon. The gap then acts as an insulator. Argon in the gap greatly increases the energy efficiency of the unit. The glass itself has a coating that reflects infrared energy (heat). This enables the insulated glass unit to allow the sun’s heat and light to enter your home, but prevents heat from being lost.

The Types of Glass to Use in Double Glazing

Buying double glazing is far more than finding the frame with the right aesthetics to suit your house, the choose the right type of glass is equally important.

The outer pane of glass is generally standard 4mm float glass, although various types of toughened, tempered or laminated glass are also common. For A rated double glazed units, Low iron glass on the outside. Low iron glass allows the maximum amount of heat to pass from the outside to the inside of the room which utalisies of any natural heat from the sun that there may be.

The inner glass is glass is a special thermal glass call Low-E Glass. This is again usually 4mm thick glass that has been coated with a very fine membrane (less than the thickness of a human hair) which reflects long-wave infrared energy (heat) to prevent heat loss from a room. Some more expensive Low-E coatings also reflect short wave infrared energy (ultraviolet radiation).

The best known brand of Low-E Glass is Pilkington K Glass. It was the original Low-E Glass and is used in many installations. Newer technology has though been developed in recent years and Planitherm (Saint Gobain) and Climaguard (Guardian Glass) have overtaken it in terms of heat retention efficiency

Energy efficient and more

Double Glazed UnitInstalling double glazed units throughout the house will help with controlling room temperatures helping to reduce heating and cooling bills. This also provides an environmental benefit is that this will also reduce your carbon footprint.

Houses in the UK are now given an energy rating to help the consumer judge their value in terms of cost saving their effect on the environment. Thermal controlled double glazing not only can dramatically increase your home’s energy rating. The benefit of this is that this could add value to your home and make it far easier to sell if you chose to move.

The insulated double glazed units also have the additional benefit of helping to reduce noise pollution from the outside. The larger the insulation gap the better the noise reduction. If you live in a noisy environment double glazing can work for you and become more than just a window.

Security of your home is also dramatically increased. The construction and thickness of the double glazed units make it much more difficult for intruders to gain entry to your property via a window. This is enhanced even more if you fit good quality window locks to each of the windows.


As you can see choosing the right type of glass for your double glazing is just as important as your choice of frame. Huge savings can be made over the lifetime of the windows that will probably more than cover the initial capital expense. If you can afford it, paying that little bit more for the most energy efficient glass could pay dividends in the long run.



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