Upgrading windows and doors helps to reduce the heating demand of a building.

Requires: Permission(s) to alter building appearance.

Energy efficient windows and doors help insulate a building, reducing heating and cooling bills as well as associated carbon dioxide (CO₂) emissions. Importantly, they also decrease the amount of noise from outside, and lessen condensation build up during cold weather.

Windows are made up of several components. Double glazing has two sheets of glass with a sealed gap between, filled with a gas and surrounded by a frame. Low emissivity glass panes are the most energy efficient. Windowpane spacers are used to keep the sheets of glass apart. These are often made of aluminium, but the most energy efficient pane spacers are made of other materials which contain little or no metal. This is because metal conducts heat out of the building, lowering the insulating effectiveness of the overall window.

The space between the panes of glass is filled with argon, xenon, or krypton as these inert gases are more insulating than air.

uPVC (unplasticised polyvinyl chloride) frames need virtually no maintenance and are recyclable. Wooden frames can have a lower environmental impact if sourced sustainably, but these require maintenance. They are often suitable in Conservation Areas whereas uPVC is not. Aluminium or steel frames are other recyclable options, with added benefits of being thinner and long lasting. Composite frames are the most weatherproof and require reduced future maintenance. They consist of a timber frame covered with aluminium or plastic.

There are a number of potential barriers or considerations when upgrading windows: Extra consideration may be required if a building is listed, in a Conservation or World Heritage Area, or has an Article 4 direction removing the right of permitted development.

When considering energy efficient doors, remember external doors are the most important for insulation purposes. The design of fire doors means that they also provide thermal insulation.