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For property owners with older windows, window insulation can create a unique problem. 

How can you achieve well-insulated, energy efficient windows without being forced to spend a lot of money on replacement windows – and, at the same time, sacrificing the treasured aesthetic of your current windows?


What is the best way to insulate old windows without losing all the features that you do love about your windows? 

In the case of heritage buildings, you will run into trouble if you try to replace your old timber windows with new aluminium or PVC ones, not only that but you’ll lose your home’s beauty, character, and traditional appeal of your heritage windows.


And, having new heritage windows made to fully replace your old ones can be incredibly expensive. This means for a lot of Australia’s classic period homes, the idea of having new windows installed to cut energy costs and better insulate your home is far from practical.  

Is DIY Window Insulation the Only Choice for Old Windows? 

As you may already realise, depending on how many window insulation tricks you’ve tried, the DIY methods don’t offer significant benefits. They also come with several drawbacks. 

Placing special insulating plastic over your glass, or a low E film for summer insulation, is going to detract from the clarity and attractiveness of your windows, without making a dent in your energy bills.

Hang up thermal drapes, insulating blinds, and anything else you can think of to create more insulation around your window glass. You’re still going to experience cold drafts, heat loss, and unwanted heat gain in the summer. 

Which means, you’ll spend hundreds on solutions that don’t truly work. Money that could have gone towards the best insulated windows on the market for older homes and heritage-listed buildings. Windows that will keep out the cold in the winters, stop overheating from happening in the summer, and will offer a quieter, healthier home with reduced noise pollution and improved air quality. 

Yes, the best windows for home insulation can do all that, and more. And, they’re more affordable than you think. 

Before giving up on insulating your old windows, take a look at how retrofit double glazing works. Using Thermawood’s patented dry Retrofit Double Glazing System, you gain all the advantages of having double glazed windows in your home – but you get to keep your old wooden windows and the original charm of your heritage windows or other old windows. 

Here’s how it works. 

Retrofit Double Glazing Old Timber Windows 

The best form of window insulation is to replace your single glazing with double glazing. A double glazing unit, also known as an insulated glass unit or IGU, is a system designed specifically to maximise the efficiency of your windows. The double glazing creates more insulation in itself, as there are two panes of glass. 

But where the real impact lies is in the small sealed air space in between the double glazing. This space slows down the movement of heat energy and prevents a huge chunk of thermal energy from making it beyond your double glazing, diminishing heat loss and stopping the bulk of solar heat gain. 

Depending on the unique needs of your property, you can tailor your IGUs for better winter insulation, more protection against overheating, enhanced acoustic performance, as well as other features like better security or a combination of the above.

The problem with getting new double glazed windows installed in older homes, is that your window installers will rip out your current timber joinery to put in a new one. You may lose the look of your heritage windows, as well as the function and style a lot of the character-rich windows of Victorian, Edwardian and Georgian homes offer, such as older double hung, awning and hopper windows. 

With retrofit double glazing, you get the new double glazing unit, but it is retrofitted into your existing wooden joinery. Thermawood uses the most advanced system on the market, converting your timber frame by creating a 15 degree angle and installing a specially-made grand adaptor complete with a patented drainage system. Then, the new IGU can be fitted within your current windows. 


We also include draft seals, and acoustic seals for noise pollution, directly into the design. They are machined into the windows, which means they aren’t going to shift or impact the movement of your windows, which can happen with a lot of other methods for sealing windows.   

Retrofitting is a simpler, less expensive process than installing new windows, which leaves your old joinery, character and heritage (if a heritage listed building) components of your windows intact. 

With Insulation for Old Windows, Moisture Control Is Critical 

Part of what makes Thermawood’s Retrofit Double Glazing System the most sensible option for insulated windows on the market today is that you won’t just have insulated windows, but beautiful, fortified windows, designed to stand up to the elements, harsh weather, and time because they are optimised for moisture resistance. 

This is particularly important with older windows. You want your investment to last, well beyond your time in your home. 

One of the biggest threats to the longevity of your windows, as well as to your indoor air quality, is water. When moisture has the chance to build up around your glass, it will drip down into your joinery, slowly damaging your windows. 

This can also lead to mould growth. You may not be able to see mould around your windows but if it’s formed, it’s impacting the air you and your family breathe. 

During the retrofit process, Thermawood window professionals will convert the windows so that the maximum amount of water can drain through the patented dry glazing drainage system. This helps to prevent condensation from ever forming and makes it close to impossible for mould to grow.


When you look at how Thermawood’s advanced Retrofit Double Glazing System was created, you can clearly see the intention behind the design. The goal has always been to create the best windows for home insulation, including for older buildings, which, after all, often experience the biggest problems with insulation and drafts. Thermawood is even certified to work on heritage-listed buildings in Australia because of our expertise in creating solutions for older wooden windows. 

There’s no reason to have to give up what you cherish about your windows in order to live a more sustainable lifestyle – and to enjoy lower energy bills and a more comfortable home!

An advanced system created specifically to help you achieve your insulation goals, at a fraction of the price of new double glazed window installation – why settle for anything less than the best for your beautiful older windows?

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Thermawood New and Retro-fit Double Glazing. For a warmer, healthier, drier home.