Doors & windows

By making sure the windows and doors in your property are energy efficient you can reduce the amount of heat lost through gaps, reduce condensation, and have more peace and quiet. This can be done in several ways. You might explore double or triple glazing, installing secondary glazing or using heavy curtains. 


The energy performance of a window depends on how well these materials stop heat from passing through, as well as how much sunlight travels through the glass and how little air can leak around the window. 

If you are thinking about changing your windows or doors you will need to think about U-values and the energy rating.  

A U-value measures the rate at which heat escapes through a fabric. The lower the figure, the better. A U-value of zero means that no heat is escaping.  

The energy-rating scale goes from A++ to E (with A++ being the best). The entire window (the frame and the glass) is assessed for heat loss, draughts and solar gain, giving a rating that indicates the overall impact of fitting that window in your home. 


UPVC are a low maintenance option. However, the Centre for Alternative Technology recommend that they should be avoided as their production is energy intensive, and they are polluting at manufacture and disposal. 

Alternatives include wood (which needs more maintenance), aluminium and composites which have wood on the inside and aluminium on the outside. 

New double glazing is required to have trickle ventilation in the frame (even if the ones you are replacing do not). This is because modern windows are more airtight than older ones. 

Double and triple glazing

Standard double-glazed windows will have air in the gap (usually 16mm wide) between the two panes of glass. Higher performing ones tend to have argon or other gases in-between. They will also have a low emissivity (low-E) coating. This allows the heat from the sun into a room and reflects heat back into the room. 

The Energy Saving Trust estimate that you will save £105 a year by replacing single glazed windows with B-rated double glazing in a typical detached home. 

Triple-glazed windows have three sheets of glass, and two gaps. This can make them better at insulating than many double-glazed windows, but it’s not always the case. 

Secondary glazing

All new build properties must be fitted with double glazing. However, not all old properties are able to upgrade. If you are in a conservation area or live in a listed building, you should consult your local planning department. In these cases, the permitted solutions may be prohibitively expensive. This leaves three possible alternative solutions to reduce heat loss (and increase warmth):draught proofing, secondary glazing and shutters or thick curtains. 

Secondary glazing involves fitting an additional pane of glass or acrylic sheet fitted over the window internally. How sophisticated it is will depend on whether or not you want to open the window (you can get glazing that slides open) or not. Detailed advice for older properties is available free of charge from Historic England. Click the link to download its guide to secondary glazing. 


To be most effective curtains should be hung flush against the wall (not on a pole that leaves gaps at the top and sides). Ideally there should be a pelmet to help trap the cold air that comes in the window behind the curtain.


The Energy Saving Trust reports you can save up to £20 per year installing an energy efficient door.  

When buying a new door, uPVC doors tend to have lower u-values. However, as mentioned above, they also use more energy in manufacture and lead to more pollution at manufacture and disposal. 

Specialist manufacturers do make very insulated wooden doors, but they tend to be significantly more expensive. 

You can improve the energy efficiency of existing doors by draught proofing so that they seal better. Find more on draught proofing here.


Heat is lost quicker through windows than through walls, and so conservatories can be a huge cause of heat loss in a home. Try to keep the door between your home and the conservatory shut as much as possible and use double glazing, blinds and shutters to help reduce heat loss and reduce over heating in summer

Installing a well-insulated external door between the rest of your home and the conservatory is a good investment as it will significantly reduce the amount of heat passing through to the conservatory in the colder months.