Energy is lost through windows in two ways: by heat passing through the glass and by warm air escaping though gaps in and around the frames. They are equally important and both can be tackled in four main ways without detracting from the appearance or heritage value of the windows:
- The windows can be repaired and their mechanisms overhauled
- The windows can be draught-stripped
- Secondary glazing can be added
- Secondary protection, such as shutters and curtains, can be used at night
The benefits of simple repairs should not be underestimated. Freeing windows to open and shut properly, repairing broken glass panes, and closing gaps around casements and sashes are the best place to start with any window improvement.
Much of the heat lost through windows is actually through leaks, and the resulting draughts are a disproportionately large source of discomfort. Providing old windows with effective draught stripping therefore yields great benefits. However, it is not a DIY job: contact a local carpenter or use one of the regional or national chains of draught- proofing specialists.
Secondary glazing is usually more expensive than overhauling and draught stripping so may not be cost effective on grounds of energy efficiency alone. It can also be visually intrusive, both internally and externally, and if poorly specified can impede the operation of shutters and the use of window ledges. However, secondary glazing does improve sound-proofing and is often chosen for the front of houses facing onto busy roads.
The benefit of shutters and curtains is often forgotten. During the the 20th century the increasing availability of cheap heating meant that people did not feel the need to close internal window shutters at night to keep the warmth in. As a result, the shutters were often painted over or removed altogether. Working shutters cannot match the performance of modern double-glazing, but they can make a big difference. They are attractive features which add to the value of the home. Similarly heavy curtains, if drawn at dusk, will also reduce heat loss.
Energy Efficiency in Historic Buildings
Secondary glazing for windows
This guidance note provides advice on the principles, risks, materials and methods for upgrading the thermal performance of windows by the addition of secondary glazing. Beside increasing the thermal performance of windows, secondary glazing can have a number of other benefits including being highly effective at reducing noise transmission.
Energy Efficiency in Historic Buildings
Draught-proofing windows and doors
This guidance provides advice on the principles, risks, materials and methods for improving the thermal performance of existing windows and doors by draught-proofing. Draught-proofing is one of the most cost effective and least intrusive ways of improving the comfort of occupants and reducing energy used for heating with little or no change in a building's appearance.
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