Retrofitted double glazing

I searched for a long time to find a glazier to retrofit double glazing. I got responses such as, “You want us to put another sheet of glass on your windows? Sure, we can do that.” I finally found one in a cold climate area and thought I was home and hosed. It has been a disappointment. The gap between the panes is only 8 mm, and there are massive thermal bridges as the metal frames are continuous inside to outside. Waste of money. Very unlike double glazing that’s common overseas which has impressed me.


Hi ! We have done this on all our compatible doors and windows with great success.
I suggest as a good start .
They will provide advise and help you to install with them or by yourself .
We are very happy with our result , Note that you cannot retrofit sash windows , unfortunately.


As @maggie1 wrote just adding a second glaze or sheet of perspex without addressing the metal frame is probably a waste of money no matter how much space is between the layers.

For aluminium framed windows doing it properly requires an insulating layer be applied to the metal frame as well as the second glazing, and depending on whether the window is fixed, sliding, or tilting the outcome can vary. Wood framed windows are obviously different, but that issue remains.

Original equipment double glazed windows are a different product to retrofitting, not to be confused.

There are a number of retrofit products on the market, some better than others, but none are ‘cheap’. I got some retrofit quotes 2 years ago and my estimated payback was over 100 years and double that for replacements not retrofits. I have fairly large windows and 4 sliding doors none that are are floor to ceiling and my retrofit quotes were in the order of $2500-4000 per window for perspective. If that quartered (75% reduction) my heating/cooling bill (which is unlikely) the payback would be more than 30 years. They forecast a realistic quarter (25%) reduction in my energy at best. Other than the ‘value’ of making the interior a bit more comfortable (more even temperature and fewer drafts around the windows) why would we do that?


Double glazing or even triple glazing was often a feature in homes in the Grand Designs UK series. I was continually amazed by the relatively low added cost of double glazing, or upgrades compared to the cost of the overall project or even as a single lump sum.

When I enthusiastically looked at the options for Australia several years previously the reality seemed very different. Double glazing appeared to require a whole new window excluding the basic outer house timber frames. The cost incrementally was not simply that of replacements plus 20-30% which seemed to the upper limit of expectations from the TV series. The costs advised were nearly double.

All of this is anecdotal in today’s values. It would seem that there are indeed two factors.

One being the likelihood many Aussie house windows do not suit a simple upgrade. It is all new windows, and perhaps even the outer framing?

The second is the everything costs twice as much in Australian factor? There are variations in glass types, separation, mounting and sealing or gas filling the void between panes, plus magic properties such as improved UV reflection to consider.

How does anyone even know that what is offered here is not a low performance $500 product being offered with a $1,000 price tag?

Or depending on where you live in Australia which products best match the local environment. We have areas with high outside humidity and moderate elevated temperatures yet others with very high outside temperatures and low humidity. These are not typical of northern Europe or the UK. (Unless you live in Alpine Australia or parts of Tassie there is no equivalence.]

Perhaps NZ has some relevant solutions?


I suggest that instead of vague assessments that some solutions are a waste of money or look good, or not so good, that you need some figures. Any supplier of double glazing solutions ought to be able to give you the heat transmittance of their product, the U value.

Your investigation should also look at whether you need to do all your windows or just some and if other improvements might be cheaper or more effective.

In the latter category if wanting to reduce heating through a window during summer the first consideration ought to be shading it. An external awning or shutter may give you a better result for less if the window gets direct sun during the day. It has the added advantage that the shade can be larger than the window and cool the wall too and it can be lifted during winter to allow the sun in. Moveability of shading is particularly important on east and west facing walls.

Despite the matter being understood for a long time there are still plenty of housing plans on the market and new houses being built that do not allow wall shading in some of our hottest climates. This simple error condemns the occupants to a lifetime of hot rooms or inflated aircon bills. This adds to all those charcoal roofs and houses oriented to the view not the sun. I know I am ranting, I’ll stop now.


The difference in requirements between hot and cold climate might be obvious but still worth mentioning. When the main problem is keeping heat out there are choices such as @syncretic pointed out . When the problem is keeping heat in and cold out it is a different slant to the problem, noting the OP referenced

which implied the latter was the problem she wished to address. In a cold climate it is generally all or nothing across the comfort sensitive living areas although there are going to be exceptions and sometimes workable shortcuts.

We installed light filtering (not opaque) honeycomb blinds. Cheaper than retrofits, a decorator item so the fashion conscious are happy curtains or other coverings are not needed, and they make a noticeable difference to comfort and the heating bill. In summer on the hottest days we put them down when it heats up so we only need to run the A/C for part days.


I want to double glaze my bedroom windows to reduce noise. Any suggestion on a reliable glazier/supplier in Melbourne area?

Welcome to the community @Richard3

I inferred your project is retrofitting so moved your post into this existing topic that hopefully has some interesting points made.

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The greater focus for most with double glazing is thermal insulation first, sound reduction a bonus.

You may find the following a useful alternative to consider. I can’t recommend the supplier, however many up here in Qld install shutters - plantation on the inside, hinged or roller shutters on the outside. They do make a noticeable difference to noise, more so solid external shutters. It might not suit all depending on your need for light and the noise level.

Noise also travels through the roof/ceiling and walls. Hopefully you have considered these too. We notice traffic noise when in Brisbane from the nearby main road. Insulating the ceiling of the townhouse ‘tin’ roof (to keep the cool out) made a significant improvement. Your situation may be very different.