Reduce bills and carbon footprint with energy efficient glazing

Energy efficient glazing helps reduce your carbon footprint and energy bills, whether with double or triple glazing, secondary glazing or just heavier curtains.

Energy efficient windows also mean:

  • A more comfortable home – energy efficient glazing reduces heat loss through windows and means fewer draughts and cold spots.
  • Peace and quiet – as well as keeping the heat in, energy efficient windows insulate your property against external noise.
  • Reduced condensation – energy efficient glazing reduces condensation build-up on the inside of windows.

However, before installing double glazing, check with your local planning office if any of the following apply:

  • You are located in a conservation area.
  • You have an Article 4 direction on your property, removing the right of permitted development.
  • The property is a listed building.

Conservation areas and listed buildings

If your property is in a conservation area or in a listed building, there may be restrictions on what you can do to the windows. These areas are of special architectural or historic interest, meaning that any work you carry out on your home must preserve or enhance the character of the area.

This does not necessarily mean you cannot replace the windows but might mean you will need to get windows that complement the character of the building and area. Double glazing can be made to look like the building’s original windows but for any changes you need to contact the local council’s conservation officer for guidance.

There are a number of non-intrusive window insulation options available for historic properties such as shutters, secondary glazing and sealed blinds. However, each historic building is considered individually.

Listed buildings have tight controls on what you can change on the outside and sometimes the inside as well, depending on their grading. Old sash windows in historic properties can be protected not only for their appearance but also the materials and methods used to make them. But secondary glazing can be a non-intrusive way of insulated historic windows from the inside and may be granted permission.

Sash windows

Sash window units are common features of period properties and can be a design feature. They consist of two vertically sliding frames, but are often badly fitting and made of single pane glass so have poor insulating properties.

If you want to insulate sash windows, there are a number of alternatives to conventional double glazing. If you want to keep the design and look of the sash windows, there are units available that are in keeping with the original design; these are fitted and sealed to prevent draughts and incorporate double glazing to reduce heat loss. The frames don’t need to be plastic but can be metal or wood with an insulated core.

An increasing number of double glazing companies offer double glazing in period properties. Replacing sash windows can be expensive so good quality secondary glazing may be worth considering.

Secondary glazing

A secondary pane of glass and frame can be fitted inside the existing window reveal. This won’t be as well sealed as a double glazing unit but will be much cheaper to fit and will still save energy. Low emissivity glass will improve the performance of secondary glazing.

Understanding energy ratings

Some window manufacturers show the energy efficiency of their products using an energy rating scale from A++ to E. The whole window – the frame and the glass – is assessed on its efficiency at retaining heat. The scheme is run by the British Fenestration Rating Council.


Windows that have an energy rating will have the u-value of the window displayed on the energy label. A u-value is a measure of how easily heat can pass through a material. Materials that let out more heat have higher u-values whereas materials that let less heat pass through them have lower u-values.

In some cases, windows with a higher energy performance rating might have a higher u-value than windows with a better energy efficiency rating. This might seem the wrong way round as lower u-values indicate better insulation levels. However, in these cases it will be that there are other aspects of the window that make them better overall, such as coating used on the glass and the gap between the glass panes.


Replacement windows will be more airtight than the original frames so condensation may build up in your property due to the reduced ventilation. If the property does not have much background ventilation, look for replacement windows with trickle vents incorporated into the frame to let in a controlled amount of ventilation.

If you start to see condensation building up around your windows, there may be a damp problem in your property. As a general rule, damp occurs when there is inadequate ventilation, inadequate heating, inadequate insulation or a combination of these. If you have started to notice condensation in between the panes of glass in the double glazing units, then it is likely that the seal is broken and the unit will need to be replaced.

Source: Energy Saving Trust