Energy Efficiency in Traditional Buildings - Dublin City Council

ENERGY EFFICIENCY IN TRADITIONAL BUILDINGS
Windows, doors and rooflights
Traditional windows are an intrinsic part of the
character of our historic and vernacular buildings. In
Ireland, most surviving traditional windows are timberframed,
vertically sliding sash windows with single
glazing. Other traditional windows include casements
or fixed lights of timber or cast iron, leaded lights and
twentieth-century metal framed windows. The quality
of the timber and workmanship found in older
windows is generally far superior to that found in
modern ones and, when properly repaired and
maintained, traditional windows will commonly
outlast modern replacements. For further information,
see Windows: a guide to the repair of historic windows in
this Advice Series.
Between 10-15% of the heat lost from a building can
be through its windows, by a combination of radiant
heat loss through the glass, conductive heat loss
though the glass and frame and ventilation heat loss
through gaps in the window construction. This is low
compared with the estimated average 25% heat loss
through the roof and 35% through external walls. Yet
windows are most often the first target of energy
efficiency works.
In terms of heat retention within a building, older
windows may appear to perform poorly when
compared to some modern windows. It is, however,
possible to repair and upgrade traditional windows to
bring them up to a similar, if not higher, standard than
modern double-glazed windows and to improve the
A pair of houses with well-maintained timber
sliding sash windows
Terraced houses with replacement uPVC-framed
windows. These windows are unsympathetic to the
character of the houses; opening outward instead
of sliding up and down, they disrupt the streetscape;
the modern glass creates jarring reflections; while
the thick frames contrast poorly with the elegant
timber sections of the original sash windows
comfort of occupants without damaging the character
of the building. Prior to considering works, the actual
heat loss through the windows should be considered.
In buildings where windows are small compared to
the overall wall area, upgrading the windows may not
result in a significant improvement in comfort levels or
in energy savings.
When considering the replacement of windows, a
number of factors should be taken into consideration.
First and foremost is the potential effect on the
character of the building and the architectural
heritage value of the existing windows. Also to be
considered are the financial cost, the energy required
to produce a new window, its embodied energy, and
the environmental cost related to disposal of waste.
Modern double-glazed window units are expensive
and high in embodied energy. The initial financial cost
and embodied energy consumption may never be
recouped by cost and energy savings on heating bills
within the serviceable life of such windows. Instead,
simple upgrading of existing historic windows can
eliminate draughts and reduce heat loss. This costs less
and is kinder to the environment than fitting new
replacement windows.
The use of uPVC in traditional buildings should
generally be avoided. uPVC is a material with very high
embodied energy which has a short lifespan as it is
difficult, if not impossible, to repair. Simple wear-andtear
often results in whole units requiring replacement
after relatively short periods of time. The manufacture
of uPVC also results in many toxic and environmentally
damaging by-products. In addition, uPVC is generally
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