Low Energy House - Low E Glass - Double and Triple Glazing
Low E glass 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
Low Emissivity Glass - Low E Glass
In order to achieve the U-values required by the building regulations low emissivity glass must
be used. Double and triple glazing units with low emissivity glass (low E) will perform better than ordinary
Low E Glass will:
- Reduce heat loss, saving energy by maintaining a comfortable environment at
lower thermostat settings.
- Reduce cold spots and downdraughts near windows, improving comfort and increasing
usable floor space
- Increase inner glass surface temperatures reducing condensation inside the
- Reduce capital and running costs of heating systems
Low E Coating
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 in the
outer face of the inner pane in a double or 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.
Transparency of Low Emissivity Glass
In most instances, the transparency of the glazing is not significantly affected
by the low E coating although a very slight tint is discernable in certain circumstances, particularly
from the outside.
Pane Separation in Double and Triple Glazing
Double and triple glazed units for house windows are generally available with air gaps from 6mm to 20mm.
In frames with narrow air gaps, the closeness of the panes can cause heat to pass from the inner pane
to the outer. Where the air space is wide, air currents can set up within the air gap which also causes
warm air to pass from the inner pane to the outer.
Double Glazed Unit Thickness
The thickness of the glass will depend on the size of the window.
In house high performance windows, the most popular air gap width is 16mm. With a glass
thickness of 4mm, the unit is 4-16-4 giving a total double glazed unit thickness of 24mm (1 inch). This size
works well for replacement window frames.
Thermally, the weakest point of a double or triple glazed unit is at the edge where
the spacer is incorporated. Spacers are usually made of aluminium, which conducts heat, and can
create a cold bridging effect at the edge of the unit. Aluminium spacers should be buried deep inside the
rebate in order to minimise a thermal bridge. Sealed units are available that incorporate
insulated spacers and reduce the cold bridge effect, improving the overall performance of the unit.
Inert Gas filled Spacers
Air is a good insulator but inert gases are better because they have lower thermal
conductivity which reduces the amount of heat that is conducted through the window. The cheapest and
most commonly used inert gas is argon, although krypton and xenon can also be used.
Gas filled units are generally used in triple and double glazing to reduce the unit depth.
Triple Glazed Windows
Expertly designed assembled and installed triple glazed windows will
significantly reduce energy usage in a new dwelling.
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
Double Glazed Windows
Old and badly fitting window frames should be replaced with energy efficient double glazed windows to save energy and improve comfort.
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
Low Emissivity Glass - Low Energy Windows