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Windows and Doors

All properties lose heat through their windows. But energy-efficient glazing keeps your home warmer and quieter as well as reducing your energy bills. That might mean double or triple glazing, secondary glazing, or just heavier curtains.

The benefits of energy-efficient windows

  • Smaller energy bills: replacing all single-glazed windows with B-rated double glazing could save you around £165 per year on your energy bills.
  • A smaller carbon footprint: by using less fuel, you'll generate less of the carbon dioxide that leads to global warming - typically 680kg a year.
  • 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 home against outside noise.
  • Reduced condensation: energy-efficient glazing reduces condensation build-up on the inside of windows.

The costs and savings for energy-efficient glazing will be different for each home and each window, depending on the size, material and installer. Double glazing should last for 20 years or more.

How energy-efficient glazing works

Double-glazed windows have two sheets of glass with a gap between them, usually about 16mm, to create an insulating barrier that keeps heat in. This is sometimes filled with gas. Triple-glazed windows have three sheets of glass, but aren't always better than double-glazed windows: to choose the most energy-efficient window look for the BFRC rating and Energy Saving Trust Recommended logo.

Energy-efficient windows come in a range of frame materials and styles. They also vary, depending on:

  • How well they stop heat from passing through the window
  • How much sunlight travels through the glass
  • How little air can leak in or out around the window

What to look for

  • Glass: The most energy-efficient glass for double glazing is low emissivity (Low-E) glass. This often has an unnoticeable coating of metal oxide, normally on one of the internal panes next to the gap. This lets in light and heat but cuts the amount of heat that can get out.
  • In between: Very efficient windows might use gases such as argon, xenon or krypton in the gap between the sheets of glass.
  • Pane spacers: These are set around the inside edges to keep the two panes of glass apart. For maximum efficiency, look for pane spacers containing little or no metal - often known as 'warm edge' spacers.

Frame materials

For all frame materials there are windows available in all energy ratings.

  • uPVC frames last a long time and can be recycled.
  • Wooden frames can have a lower environmental impact, but require maintenance. They are often used in conservation areas where the original windows were timber framed.
  • Aluminium or steel frames are slim and long-lasting, and can be recycled.
  • Composite frames have an inner timber frame covered with aluminium or plastic. This reduces the need for maintenance and keeps the frame weatherproof.

Energy rating

Some window manufacturers show the energy efficiency of their products using an energy rating scheme from A to G - like the one used for appliances such as fridges. 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 (BFRC).

Energy Saving Trust Recommended

The most efficient windows (B and above) can also carry the Energy Saving Trust Recommended logo.

Ventilation

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

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

Windows in period properties

If you live in a conservation area or a listed building there may be restrictions on what you can do to your windows. There are a number of non-intrusive window insulation options available for historic homes such as heavy lined curtains, shutters, secondary glazing and sealed blinds. However, each historic building is considered individually so check with your local council to see what options are available to you.

Conservation areas

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 your 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 your building's original windows, but for any changes you do need to contact your local council's conservation officer for guidance.

Listed buildings

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.

There are other ways to make historic buildings more energy efficient but you will need to consult and apply for permission from your local planning authority.

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 qualities.

If you want to insulate your 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, though, so good-quality secondary glazing may be worth considering.