Low Energy House - Triple Glazed Windows - Triple Glazing
Triple glazed windows consist of three sheets of glass, each separated by an air gap. The air
gaps provide the insulating layers that slow down the heat loss and reduce the opportunity for
condensation to form
Expertly designed, assembled and installed, triple glazed windows will
significantly reduce energy usage in a NEW dwelling. If the external walls of an EXISTING house have little, or no, insulation then it may be preferable to replace the existing windows with Double Glazed Windows, as Triple Glazed Windows are more expensive and unlikely to conserve more heat
Triple Glazed Windows - Super Insulated House
Energy efficient windows constructed to current standards offer excellent thermal performance in houses. In the case of new super insulated houses, the windows are the weakest point thermally in the building envelope. To overcome the problem, it is advisable to install high performance triple glazed windows with low-E glass and inert gas fill.
Triple Glazed Windows - Construction
A triple glazed window uses three sheets of glass, each separated by an air gap. The air gaps provide the insulating layers that slow down the heat loss and reduce the opportunity for condensation to form. Expertly designed, assembled and installed, triple glazed windows will significantly reduce energy usage. The main thermal advantages of triple glazed windows are: the conservation of heat, the elimination of draughts and the resistance to condensation.
Developments in Triple Glazed Windows - Design
Until recently, triple glazed windows were produced as an enlarged version of double glazed windows and as a result the frames were too deep to be accommodated within current wall thicknesses and were expensive to produce. Recent developments in triple glazing windows have resulted in slimmer profile frames and flush sash design that are pleasing in appearance and deliver enhanced performance at an affordable price.
Multiple Panes of Glass - Triple Glazed Windows
It is physically possible to manufacture high performance windows with more than three layers of glazing but the contribution of each successive layer to the thermal value reduces to the point where the thermal advantage does not constitute value for money. With several glass layers the window framing becomes deeper to accommodate and with more glass the light transmission and clarity of vision reduce.
Triple Glazed Windows - Frames
Heat loss occurs through the window frame as well as through the glass. Window frames and sashes are available in a variety of materials with differing rates of conductivity. House windows are generally manufactured from low conductivity materials, like from softwood, hardwood, pvc-u (u-pvc), glass fibre and composites. Insulated hollow frames can further reduce heat loss and improve comfort.
Vacuum Glazed Windows
The world’s first commercially available vacuum glazing offers the thermal performance of conventional double glazing, with the same thickness as a single pane of glass.
Triple Glazed Windows - Low Emissivity Glass (Low-E Glass)
Low emissivity (low E) glass incorporates a very thin layer of metallic
coating on one surface. To protect it from wear, the low E coated surface is positioned on the
outer face of the inner pane in a triple glazing layer. The coating allows heat from the sun to enter
the building but significantly reduces heat loss from inside the building by reflecting radiant heat
back into the room.
Triple Glazed Windows - Glass Spacers
The three panes of glass are each separated by a ‘spacer’. Most spacers are constructed of either thin gauge steel or aluminium, for reasons of thermal expansion stability and cost. To reduce heat transfer through the spacer and to increase overall thermal performance, the spacer may be constructed of fibreglass or a hybrid design of metal and plastic.
Triple Glazed Windows - Inert Gas Fill
Air is a relatively good insulator but inert gases are much better due to their lower thermal conductivity. The most commonly used inert gas in triple glazing units is argon. The inert gases krypton and xenon are thermally more efficient but are more expensive.
Triple Glazed Windows - Air Gaps
The maximum insulating efficiency of a triple glazed windows is determined by the width of the spaces containing the gas. Too little space between the panes of glass results in radiant heat loss, across the gap, from one glass pane to the other. Too wide a gap results in convection currents occurring in the gap causing temperature differences and heat transfer between the panes.
Total Estimated Heat Loss
To properly estimate the heat loss through any window, it is necessary to take into account not only the pane and gap, but also the thermal properties of the sash, frame and sill. Thermal bridging through any of these can lead to huge energy losses.
Heat Recovery Ventilation
When designing windows to achieve high thermal efficiency ratings, it is usual to omit the air vent. In such cases the house will be ventilated by a mechanical heat recovery ventilation system.
BFRC Window Energy Rating
The BFRC window rating allows comparisons of different window types. The ratings take into account the amount of heat lost through windows as well as how much air leaks into or out of the window unit when it is closed.
Double Glazed Windows
Old and badly fitting window frames should be replaced with energy efficient double glazed windows to save energy and improve comfort.
In order to achieve the U-values required by the building regulations low E glass must
be used in double or triple glazed windows.
If you have one or more of the windows replaced in your home then Building Regulations will apply
to the work. If the installer you employ is registered you will not have to involve the Building Control
Service. On completion of the work the registered installer must give your local authority a
certificate confirming that the work complies with Building Regulation
Triple Glazing - Low Energy Windows - Energy Efficient Windows