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
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:
What to look for
For all frame materials there are windows available in all energy ratings.
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.
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.
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 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 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.