Double glazing or secondary glazing – which should I choose?

Double glazing, secondary glazing, triple glazing and even quadruple glazing. There are plenty of options open to homeowners when they look to upgrade their windows.

Despite its soundproofing and energy efficiency gains, triple glazing is only a small but growing part of the market. Quadruple glazing is only used in the most extreme environments.

In this guide, we will look at the more popular choice, between double glazing and secondary glazing.

Double glazing works by having a gap between two layers of glass. This reduces the transmission of energy from the warm air in your home to cold air outside. The gap is often filled with an inert gas like argon, which is a poor conductor of heat, and thus a good insulator.

It also works the other way around – in the hottest days of the year, it insulates your cooler home temperatures from outside.

It also dampens noise, keeping your home quiet.

Secondary glazing is best understood as another window behind your original. There is a much bigger gap between the two panes and the gap is simply air rather than argon or another inert gas. You slide open the secondary glass to access the outer window.

It is cheaper to install and it does not require any changes to your outside windows, which could be important if your home is listed or in an area where planning rules are tightly managed, like a conservation zone.

And it helps block draughts and noise.

According to supplier Everest, the average uPVC casement double-glazed window will cost £1,200, meaning for a home with eight windows, prices will be just under the £10,000 mark.

Secondary glazing, meanwhile, costs an average of £400 a window, according to Checkatrade.

Much depends on your budget and local planning rules.

In most cases, you won’t need planning permission to fit double glazing so long as it looks similar to the window you are replacing. But if that is a timber sash window, those can run into thousands of pounds apiece.

If you are looking to trap in more heat, secondary glazing could offer a cheap way of doing that, and you can even fit it yourself if you have a good track record in do-it-yourself projects. You can order the glass made to measure. Just bear in mind that wonky window bays and heavy glass could make for a troublesome project.

Also consider that it won’t look as neat as a new set of windows, nor will it offer the same level of efficiency.