What is secondary glazing​?
What is secondary glazing​?
Secondary glazing is a fully independent window system installed to the room side of
existing windows. The original windows remain in position in their original unaltered
form. Secondary glazing is available as openable, removable or fixed units. The
openable panels can be either side hung casements or horizontal or vertical sliding
sashes. These allow access to the external window for cleaning and the opening
of both the secondary glazing and external windows for ventilation. Fixed forms of
secondary glazing are designed to be removed in warmer months when the thermal
benefits are not required.​
Secondary glazing when carefully designed and installed allows the original windows to be retained unaltered, and where necessary repaired, whilst reducing air leakage and conducted heat losses. As a result there is no loss of historic fabric and in most cases the installation is easily reversible.​
Research has shown heat losses by conduction and radiation through a window as a whole can be reduced by over 60% by using secondary glazing with a low emissivity (Low-E) hard coating facing the outside. The research has also shown that further savings can be made if the secondary glazing uses insulating frames or incorporates double glazed units. Besides increasing the thermal performance of windows, secondary glazing unlike double glazing can have a number of other benefits including being highly effective at reducing noise.
Repair to existing windows.
Repair to existing windows.
Traditional timber and metal windows can almost
always be repaired, even when in very poor
condition and normally at significantly less cost
than complete replacement. The timber used in
the past to make windows was of a high quality
and very durable. Many Georgian and Victorian
windows are still in place today whereas modern
softwood windows can need replacement after
only twenty years. Repairing windows is the best
way of maintaining the visual character and
architectural significance of a building’s elevation
and can add to its value.
Before starting any upgrading work such as
draught-stripping or the addition of secondary
glazing, assess what repairs are needed to make
the windows fully operational. Windows decay
over time so regular maintenance, cleaning and
painting is always a good investment.
Draught proofing or secondary glazing?
Draught proofing or secondary glazing?
Draught-proofing is usually the first option to
consider for improving the thermal performance of
windows in an older building. As windows are often
a major source of air infiltration, draught-proofing
is one of the best ways of improving comfort and
reducing energy use, with little or no change to a
building’s appearance at minimal cost.
However, secondary glazing can provide a
considerably higher thermal performance than
draught-proofing alone. It may also be chosen
where installing draught-proofing seals to the
windows is particularly difficult. Similarly many
metal-framed windows have gaps that are too
large to seal. Windows with leaded lights may
allow air infiltration around the lead which can
only be satisfactorily addressed with the addition
of secondary glazing.
Depending on the building’s use, location and the
occupants’ comfort requirements other benefits
of secondary glazing, such as noise reduction,
may have a bearing on the design solution.
If secondary glazing is the preferred solution then
the outer windows are best left without draught-proofing
so that there is a degree of ventilation to
the air space between the outer windows and the
secondary glazing to prevent the build-up
of condensation.
