External shutters provide extra security 
as well as a way of controlling light and heat loss.
External shutters provide extra security as well as a way of controlling light and heat loss © Linda Hall
External shutters provide extra security as well as a way of controlling light and heat loss © Linda Hall

Improving Thermal Performance of Windows and Doors in Historic Buildings

This page provides advice on improving the thermal performance of both windows and doors, which can be upgraded relatively easily without detracting from their appearance.

Care, repair, upgrading and modifying windows

Traditional windows make an important contribution to the visual character and heritage significance of historic buildings and areas. They are integral to the design of older buildings and can be important artefacts in their own right, made with great skill and ingenuity from high quality materials not generally available today. When contemplating improvements to save energy and reduce fuel bills, owners and residents of historic buildings often think first about replacement windows.

Many traditional windows have been lost because old windows are thought to be burdensome to maintain and not energy efficient. But research carried out by Historic England has shown that they can be made to meet current thermal performance requirements economically and with minimal harm to significance. Furthermore, they are durable, functional and repairable and if properly maintained will last longer than many types of replacement. Therefore, this ‘repair not replace’ approach makes good social, economic and environmental sense.

This 2017 guidance should be read alongside our advice Modifying Historic Windows (August 2020) which addresses:

  • Conserving and improving historic buildings as part of climate action
  • Energy-saving considerations and windows in historic buildings
  • Making changes to windows in listed buildings
  • Making changes to windows in unlisted historic buildings

Curtains, blinds and shutters

Our research shows that curtains, blinds and shutters can significantly reduce heat loss through glass. Heavy curtains reduced heat loss in sash windows by 39% and well-fitting shutters reduced heat loss by 64%.

Draught-proofing windows and doors

Older buildings are prone to lose heat through gaps, which develop as various building elements move and distort over a long period. This can often be the case with windows and doors where draughts develop.

Draught-proofing is one of the most cost-effective and least intrusive ways of improving the comfort of occupants and reducing energy use with little or no change to a building’s appearance.

Make sure you repair windows and doors before embarking on any draught–proofing measures.

Secondary glazing for windows

Secondary glazing is a fully independent window system, installed on the room side of existing windows. The original windows remain in position in their unaltered form.

Research has shown that heat loss can be reduced by over 60% by using secondary glazing with a low emissivity hard coating facing the outside.

Insulating dormer windows

Older buildings often have dormer windows which come in a variety of shapes, sizes and materials. If the main roof is being insulated then we would advise you to insulate any dormer window which is a part of that roof.

Learn more

View the recording of the 2020 webinar: Traditional windows: Care, repair and improving energy efficiency.

In this webinar we review the contribution made by traditional domestic windows to the heritage values and significance to historic buildings and places. We look at practical aspects of maintenance, repair and upgrading, and consider the whole-life carbon costs compared to replacement. Finally, we discuss development management and building control issues to be considered when alteration or replacement are contemplated.

For the best webinar experience, please use Google Chrome browser or download Adobe Connect.