Things to consider before retro fitting your home with double glazed windows

Two images showing demolition of walls and fitting new windows

Here is my experience as an owner builder with retro fitting double glazing.

Think about why you are fitting double glazing

The ‘experts’ I asked suggested there may not be a great return on investment (ROI) with retro fitting double glazed windows to your typical brick veneer house. This is because the windows are expensive and the potential savings from improved energy efficiency are not that great. Brick veneer house are usually poorly insulated and drafty. While the windows may perform well a lot of heat will leak through other parts of the building. If the new windows are poorly fitted, they will also leak between the window and wall. You’ll get a better ROI using wall and roof insulation, along with good curtains and pelmets.

Double glazing can provide a noticeable improvement in comfort. But this depends on the windows you are replacing. You will notice a great improvement if you replace nasty aluminium windows. However, as timber frames don’t transfer much heat you may not notice much of an improvement.

What most people don’t realise is even the very best performing windows are only something like 30% as good as a reasonably well insulated wall. If you have lots of glass, even if it is good double glazing you are still going to have problems with controlling heat transfer. This is why Passive Houses often have small very scientifically sized windows.

What to consider when choosing windows

There is more to good windows than just glass. Aluminium double glazing without a thermal break is not very effective as the heat just goes straight through the metal frame. Aim for frames made of uPVC or something with a ‘thermal break’. Take the time in the showroom to look at the quality and functionality of things like frames, reveals, hinges, locks and opening mechanisms. The ones I fitted have some awkward locks and fly screens. And it sh*ts me when I go to unlock the sliding windows. Every time you use the windows, you’ll notice the shortcomings in functionality and quality.

Fitting windows

My final tip relates to fitting. Be careful of the weights. One of my very large windows required 5 mates and some Egyptian style ropes and ramps to fit. It was dangerous and difficult. I found out later that if this window had it been a bit bigger the manufacturer would have shipped the frame first for fitting and fitted the glass later.


Having said all of this, I’m very glad I fitted double glazing in my renovation. I did it as part of larger reno, so I was able to add a lot of wall and roof insulation. I spent time carefully sealing between the window frame and the wall opening. I also removed walls and expanded openings which greatly increased the amount of glazing so high-performance windows were important. In the end I achieved a 6 star rating for a retro fit to a 70s brick veneer extension. Here’s a bit more info Bayley st renovation.