Whilst double glazing is a standard feature on most garden office and studios specifications, some suppliers go a step further and offer low emissivity glazing. Low E glazing has a special coating on the outside of the inner pane of glass, this coating allows light and heat from the sun to pass into the room whilst preventing heat generated within the room from escaping out of the window. Low E glazing makes a garden office or studio warmer in winter and cooler in summer, which means the building is comfortable to use all year round and cost effective to run.
So how does it work? First we need to look at how heat from the sun and heat generated from within a room differ. Heat from the sun is a form of short wave radiation whilst heat generated from within a room is long wave radiation. With normal double glazing, in winter the long wave radiation escapes through the glass to the cool outside, whilst in summer too much shortwave radiation from the sun penetrates the glass making the room hot, Low E glass overcomes this problem, the special coating reflects the long wave radiation back into the room in winter and in summer filters the amount of short wave radiation that enters the room.
There are two types of Low E coating, a hard coat or a soft coat. Hard coat Low E glass is known as a pyrolytic coating and is applied during the float glass process, the coating is sprayed onto the glass at a very high temperature. Hard coat Low E glass is very durable and can be tempered after its been coated, on the downside hard coat Low E glazing has a slight haze which can be visible at certain angles. Hard coat Low E glazing has a higher u-value than soft coat Low E glass (in u-values the lower the value the better). The leading name in hard coat Low E glass is Pilkington K glass.
Soft coat Low E glazing is created in a vacuum chamber and consists of optically invisible layers of silver and metal oxide. Soft coat Low E glass produces low u-values, allows high levels of light transmission, but up to 70% less ultra violet transmission than standard clear glass. On the downside soft coat Low E glass is difficult to handle and glass has to be tempered before it is coated. Soft coat Low E glass can only be used in double and triple glazed units where as hard coat Low E can be used on single panes of glass, it is also generally more expensive than hard coat Low E glass. SGG Planitherm Total is an example of soft coat Low E glass.