May 11, 2018: DIY Retrofit Double-Glazing

A bit over a year ago I made a trip down to Sydney to do an Energy Assessment on an existing house in Epping. Probably built around 1950 on a west-facing site, this house had a tendency to get unbearable hot in the summer time and uncomfortably cold in the winter. Among a long list of recommendations on how to improve the comfort and energy efficiency of the house I suggested that adding double-glazing to some or all of the windows would be beneficial.

There are a few ways to retrofit double-glazing into an existing house. The best (and most expensive) way is to completely remove and replace the existing windows, frame and all. This is what we chose to do on the cottage next to the Greeny Flat as documented in the following video.

This is pretty big job which made sense for us because we had completely removed the old fibro cladding and wanted to ensure that there was no painted timber exposed on the outside of the cottage (because low-maintenance and durability were priorities for us). So we replaced the single-glazed timber windows with double-glazed aluminium ones.

Another (somewhat less expensive and disruptive) option is to just replace the glass in the existing window frames. There are a number of companies that offer this service and one that looks very promising to me is called ‘Twin-glaze‘. They have a very clever system which allows them to remove the glass from an aluminium window frame and replace it with double-glazing without removing the existing frame. I haven’t used this system so I don’t know how well it works or how much it costs and I’d love to hear from any readers who have used it.

A third option is to add a second pane of  ‘glass’ (usually it’s actually perspex) to the inside of the existing window frame. The most well-known company that offers this service is called ‘Magnetite‘ because they use a magnetic strip around the edge of the perspex to hold the double-glazing tight to the existing window frame. On my sister’s house in Canberra she used a combination of total replacement of some of the larger windows (and sliding doors) plus adding ‘Magnetite’ panes to the rest of the smaller windows and to the skylights. She’s very happy with the result but it certainly wasn’t cheap.

For the house in Epping, the owners, Margaret and Brendan, took a similar approach. They replaced some of the windows completely but decided to add double-glazing to an existing pair of french doors that open out to a west-facing deck. They got a quote from Magnetite but thought it was more than they were prepared to spend. So they figured out a way to do it themselves.

Here’s what they have to say about their DIY double-glazing.

You may recall when you came to our house the French doors in our lounge room. We got a quote from Magnetite to retrofit double glazing and total cost was $1529. We decided that we would have a crack at doing this ourselves. After a couple of hours work the job was completed for a total cost of $352. A local plastic company supplied 3mm clear acrylic cut to size and the magnetic tape and steel tape for secondary glazing was supplied by a UK company (couldn’t source it locally). I will note that the Magnetite product uses 4.5mm acrylic but I’m happy with the end result and the significant cost saving.

DIY ‘double glazing’ retrofit photos are attached. We attached the magnetic tape to the acrylic then stuck the metal strip onto the tape. Then we just removed the backing to attach to the French doors, as this made it much easier to manage positioning.

Margaret and Brendan's French Doors with their DIY Double-glazing installed.

Margaret and Brendan’s French Doors with their DIY Double-glazing installed.

If any of your readers are interested the supplier of the tape is Direct Products UK (I purchased via ebay). The item was magnetic tape & steel tape secondary glazing 30m kit for white window frames.

We are also very happy with our solar installation and are pleased to see that after charging the PHEV during the day we are still exporting to the grid.

With the Enphase monitoring we get the power usage and net energy figure.

A screenshot of their 'Enphase' solar power system monitoring.

A screenshot of their ‘Enphase’ solar power system monitoring.

Also we finally received our Flir thermal camera (a very long process to get one into Australia, and I had to sign my life away to say that it wasn’t going to be used in US etc). So we have been looking at the outcome of our on-going renovations (have started recladding with insulation & sarking & have also installed 6 new double glazed UPVC windows).

Congratulations Margaret and Brendan! Upgrading the energy performance and comfort in an old house can be a real labour of love (not to mention quite costly). They’ve got plenty more to do but they’ve already achieved a fantastic amount (even buying their own infrared camera to help them identify areas of heat loss or gain) and, in the process, figuring out how to install DIY retrofit double-glazing for a VERY reasonable cost.

Thanks very much for sharing this information with the rest of us.

A Nice Bit of Good News

South Georgia Island sits just above the Antarctic Circle in the Southern Atlantic Ocean (Image Source:

South Georgia Island sits just above the Antarctic Circle in the Southern Atlantic Ocean (Image Source:

To finish up this week I’d like to give a shout out to my brother George who has been deeply involved over the last five years with an ambitious and challenging effort to eradicate rodents from South Georgia Island. This was the largest rodent eradication project ever attempted and has just been declared a success.

As you can read in this New Atlas article

The task of the project was to cover 1,087 km² (419 mi²) – an area eight times larger than any previous rodent eradication effort that included some of the harshest, most mountainous terrain imaginable….

South Georgia Heritage Trust is delighted to declare that its Habitat Restoration Project is complete and that invasive rodents have been successfully eradicated from the island.

Congratulations George (and the rest of the team), we’re very proud of you.

7 comments to May 11, 2018: DIY Retrofit Double-Glazing

  • chris blaxland

    Rodent eradication programme is active on Lord Howe Island, but they have some objections – it will involve airdrop of baits into areas deemed too difficult to reach. The concern is that these baits may be eaten by the several species of unique birds, notably the flightless LHI woodhen and the LHI silvereye. In “urban” areas they use baiting stations made of plastic plumbing to hide the baits.

    Current plan is to breed some replacement stock in captivity, and release them after the baiting, now scheduled for 2019.

  • I’m curious how this went. You posted this in May so as it was getting colder in Oz.

    Not it’s October so summer is coming. Did the DYI hold up over winter? Did the bill go down?

    I guess that’s what it really comes down to. I know the cost of really double glazing is not cheap. But it works. So I’d be very curious to know if it works as good as DYI double glazing.

    • admin

      Those are good questions Debbie which I can’t answer because I was just passing on the information from one of our other readers. So I don’t know how it held up over winter but I’ll let you know if I can find out.

  • Chris Welsh

    Hello Andy
    I am trying to double glaze a light well in the ceiling of our main room. The house is well insulated but a lot of the heat disappears up the light well. I like the magnetic tape idea but wonder if there is any chance of it dropping. The ceiling height is huge and a falling window could inflict serious damage on someone below!

    • admin

      Sorry for the slow response Chris, I would agree that a window falling from such a high ceiling could be horrifying. The “Magnetite” system uses lightweight clear perspex rather than glass if that makes a difference. You could probably also add some screws for added safety.

      Hope that helps.

  • Jeff

    Re the falling glass (etc) panel:
    Maybe a metal tab, similar to what is used on some picture frames to hold the glass in, only on a larger scale. A piece of metal with a hole at one end. A screw goes through the hole into the frame. Then swing the tab over the frame of your double insulating panel (glass, perspex etc). Use one or two along each edge.

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