Double Glazing vs Secondary Glazing: Which Is Better?
Windows can account for a noticeable share of heat lost from a home. Replacing them is a major expense, though, and not always the best first step. This guide compares the main options so you can decide what fits your home and budget.
Double glazing
Double glazing uses two panes of glass with a sealed gap between them, often filled with a gas such as argon, and usually with a low-emissivity coating that reflects heat back into the room. It cuts heat loss compared with single glazing, reduces noise and can make rooms feel more comfortable by reducing cold radiation off the glass.
Look for the window energy rating, such as the British Fenestration Rating Council (BFRC) label, which grades windows from E up to A++. A higher rating means better performance. The frame matters too: uPVC, timber and aluminium frames all have different properties and costs.
Triple glazing
Triple glazing has three panes and gives better insulation and noise reduction, but costs more, is heavier and may not repay its extra cost in a typical UK home. It can make sense in very exposed or noisy locations, or in new, very well insulated homes.
Secondary glazing
Secondary glazing adds a second pane inside your existing window, with a gap in between. It is often the best option for listed buildings and conservation areas where replacing the original windows is restricted. It can be nearly as effective as double glazing for reducing draughts and noise, and is usually cheaper. Some systems can be removed in summer.
Cheaper alternatives
- Window film: clear plastic film fitted to the inside of the frame creates a thin layer of air. It is cheap and temporary and can help in the short term, though it is not as durable.
- Heavy or thermal-lined curtains: especially effective over single glazing if closed at dusk.
- Draught-proofing: sealing gaps around existing frames can make a bigger difference per pound than new glazing. See our draught-proofing guide.
- Repairing existing timber windows, which can often be restored and fitted with draught strips.
Is it worth replacing windows?
Replacement windows usually pay back slowly in energy savings alone. Other benefits include comfort, security, noise reduction and the appearance and value of the property. If your windows are old, damaged or have failed seals, replacement may be sensible. If your windows are in reasonable condition, it is often better to start with loft insulation and cheaper fixes first.
Choosing an installer
Use an installer registered with a competent person scheme, such as FENSA or a similar one, so that the work complies with building regulations and you receive a certificate. Get several written quotes and compare the glazing specification, frame type, guarantee and what is included. Be wary of unrealistic claims about savings or pressure to sign on the day.
Before you spend, check whether you live in a conservation area or a listed building, and whether any permissions are needed.