Folding sliding doors are quite often used in commercial buildings, restaurants and hotels, as well as in the home. They are a great asset for any building, large or small. The entire external facade of a room can be opened up during good weather conditions allowing access onto a terrace. For larger openings aluminium sliding folding doors are the preferred choice due the inherent strength and slim line profile that aluminium offers.
An example of opening up a facade to enjoy the great outdoors
However, because of the huge areas of glass involved, which is usually floor to ceiling in the case of sliding folding doors, the thermal efficiency of the glass has to be a major consideration.
Thermal Efficiency for Glazing
Windows, especially in large sliding folding patio doors, are an easy target when it comes to heat loss from a building. The glass in sliding and folding doors is obviously not of the same thickness as the surrounding walls and therefore more difficult to insulate. The heat flow through materials such as brick, masonry and glass etc is measured by the U value (overall coefficient of heat transmission). Calculating the U value takes into account the materials and the method of construction. For example, an exterior wall of a house could consist to layers of brick/masonry laid in parallel with an air space. The air space could be filled with an insulating material thus reducing the heat that will transmit through the over wall structure. U value is measured in W/m2ºC which is the metric version. The imperial version is BTU/hrft2 ºF. The lower the U value the lower the heat loss.
Building authorities over the years have been officially lowering these U values for all components that make up a building. Glazing will never be able to compete with walls for example. Some think that the answer is to reduce the size of the windows but this leads to an unattractive, dreary and dark environment in the home and work place. This solution would definitely rule out the use of sliding folding glass doors due to the vast are of glass involved.
Recent thinking, however, has suggested instead of trying to compare the U values for glass and walls that considerations, in the case of glass, should take into account other benefits that windows offer such as they let in heat and light making the interior of room more attractive and comfortable.
The aim is to produce an energy efficient window. An energy efficient window will try to conserve and contain the heat within a room together with keeping out the wind and rain. At the same time an energy efficient window will allow through the free energy that comes from the warmth of the sun.
This thinking has lead to the ‘Window Energy Rating’. This system will rate a window system in a similar way to e.g. on white goods such as a fridge or washing machine, which consumers are already quite familiar with. The rating will be A to G. The Window Energy Rating is in essence an Energy Index. This index will show how much energy a window will save or lose after installation. In calculating the index the building type, climate conditions of the local area, indoor temperature of the building and the window structure will be taken into account. The rating will apply to the complete window system i.e. the glass and the frames not the individual components.
Look out for the energy rating label
So when deciding on an aluminium folding sliding doors or timber folding sliding doors or any other materials used in fold and slide doors, look for what energy rating is being offered by the manufacturer.
Internal folding doors may also be interesting reading.