double glazing ebook windows

Double glazing and alternatives for your home

If my clients’ projects had an unlimited budget, I would recommend double glazing throughout.

Double glazing is not only a better thermal barrier than regular single-glazed windows, it can also be a form of soundproofing.Since most people do have to stick to a budget, I have explained the options below.

Full double glazing

In construction there are a number of different engineering disciplines – types you might come across in the residential sector are shared here.

Annealed glass

Whilst annealed glass in a single-glazed window is easy to break, in a double-glazed window it’s less so.


Because the air cavity acts as a shock absorber.

Laminated glass

As with single-glazed windows, laminated double glazed ones essentially contain four panes of glass: two either side of the cavity with a vinyl interlayer.

Argon gas

Regardless of the type of glass, there’s also the option to fill the cavity between panes with argon gas.

Argon gas is about 40% more dense than air and improves the thermal performance of double glazing by around 15%.

Krypton gas

For the coldest parts of the country, krypton gas is twice as dense as argon gas and further slows down the transmission of thermal energy through the windows.  


As an alternative to all new double-glazed window and door joinery, there’s retrofitting. This is when you keep your existing windows and doors, but the single pane of glass is removed and replaced with double glazing.

It’s a more cost-effective option at roughly half the price of full double glazing. With retrofit double glazing, you can only double glaze within the limitations of the existing joinery – what this means is that the gap between the two panes of glass is much narrower and therefore less effective as a thermal and acoustic barrier.

The larger the gap, the better the performance.  

Secondary glass

The final option, at roughly a third of the price of full double glazing, is secondary glass.

This is when a layer of glass is installed against existing glass in your existing windows and doors.

This is nowhere near as effective as double glazing, or even retrofit double glazing and is usually used as a temporary measure rather than a permanent solution.

For example, if you have bought a do-up and won’t be in a position to design, consent and renovate for a couple of years, then you’d probably benefit from secondary glass – especially if you’re going to move or change the windows and doors anyway.

If the windows won’t otherwise be touched, then it’s worth the upfront investment.

Bonus tip

If you can’t afford new double glazing throughout, then prioritise the cold side of your home.

In the southern hemisphere, that would be the south-facing side as it gets less sun and therefore takes longer to warm up.


My Ultimate Guide to Windows, Doors, Ceilings, Stairs & Trims ebook breaks covers all the decisions you need to make, and all the information you need to make them. I cover everything from window and door anatomy, to type of glazing, ways to dress your ceilings, different trim styles and profiles, and all things staircase related. Need help with these decisions? I've got you covered.