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With the latest advancements in window technology, heritage double glazing isn’t just possible, it’s one of the best investments you can make in your home. 


Well-insulated windows will add value to your property, whilst also lowering your energy expenses and making your home more comfortable.


This wasn’t the case years ago, which is why a lot of heritage property owners assume they are stuck with their single glazed heritage windows and all the problems that come with old, outdated windows – high energy bills, noise pollution, risk of mould growth, and even safety concerns.


The fact is, whilst your beautiful decades or century-old property has remained largely the same over the years, the world around it has changed dramatically. 


It’s louder. 


Less safe. 


And, keeping your home comfortable is an expensive uphill battle. Those old windows aren’t capable of living up to the demands and pressure of the modern world.


But, how can you upgrade your heritage timber windows without losing the original aesthetic and heritage designation? You can’t exactly rip out all that charm and history and replace it with a PVC or aluminium window.


There is a solution – one that solves the challenge of having to maintain your building’s heritage status, as well as every other issue outdated windows present.


By retrofitting your existing windows with new double glazing yet retaining your timber joinery – and, in fact, improving upon it with Thermawood’s unique dry glazing system – you can enjoy a seamless and much-needed upgrade to your heritage windows.


The Double Glazing for Heritage Windows Process Explained


To retrofit heritage timber windows with double glazing, Thermawood uses a special Retrofit Double Glazing system. At the heart of this method is a patented dry glazing draining system. 




Typically, one of the biggest concerns with double glazing is the risk of moisture build up in the rebate. If the job isn’t done well, water can form on and in between the double panes of glass. Something as simple as moisture in the rebate around the double glazing will cause the seal of the double glazing to fail. This moisture will also cause the timber frame to rot and even worse if the double glazing is under warranty, it may not be replaced due to improper installation.


What Thermawood has done to solve this problem is to develop a way to ensure the window is well drained and allows for evaporation, without sacrificing the look or operation of the heritage windows in any way. Basically, if water gets into the glazing rebate, it needs to be able to get out and this is what the Thermawood system is designed to do.


By removing a small portion of the window frame, a 15-degree slope is created at the bottom of the existing frame to create a deeper glazing rebate. This allows Thermawood window professionals to install the specially made grand adaptor and the dry glazing system. 


Then, the insulating glass unit, or IGU, is securely fixed in place and a front seal is attached. The final component is the window beading, which has been specifically designed for maximum evaporation. 


The whole process can be completed within a matter of hours, leaving you with a new, superior double glazed window that operates flawlessly, yet still offers the classic character and visual appeal that heritage windows are highly valued for.


The Advantages of a Proactive Heritage Double Glazing Approach


Today’s window technology allows for seamless heritage window restoration. The goal shouldn’t be simply to retrofit your old timber windows, but to evolve them, bringing your heritage windows into the 21st century.


For a lot of places like Sydney and Melbourne, these buildings are close to one hundred years old. This means, they are more vulnerable than your typical modern home and they require a more carefully-considered system in order to be properly restored.




Retrofit double glazing offers a way to replace the single glaze with a double glazed unit as the existing wooden frame remains in place. Retrofitting also is less expensive than installing new window frames and the insulating glass units. But, when it comes to heritage timber windows, it takes more than just a standard retrofit job to get lasting results.


In order to preserve Australia’s beautiful heritage homes, the environment and your budget, Thermawood took the time to find a solution for each unique challenge that heritage restoration and double glazing presents.

  • The patented dry glazing system encourages water to evaporate, stopping condensation from forming and preventing problems with mould, wood rot and poor indoor air quality.


  • Sash windows are re-weighted to retain movement.


  • Draft seals are machined in rather than stuck on, which is what a lot of window companies do – this can impair the window’s movement. Draft seals that are stuck on also tend to (you guessed it) fall off.


  • Refurbishing wooden window frames is also part of the process – any area that needs to be refurbished to make sure the window operates like new is taken care of.


As a result, you – and the generations that come after you – can enjoy all the benefits of a properly sealed double glazing unit, within your heritage window. It will look the same yet function like a new window.


How to Get Optimal Results When Double Glazing Your Heritage Windows


Being able to achieve serious insulation without sacrificing the original aesthetic or worrying about your old timber frames rotting or becoming damaged is monumental for heritage homeowners. The negative financial and environmental impact of outdated windows, especially when added up over time and compounded by the number of heritage buildings in Australia, is very real.


A lack of insulation tends to be a major issue because of the way the buildings were originally constructed. And, if your property was renovated at some point, you may have even more insulation problems to contend with. A lot of heritage renovations happen at the back end, such as adding on a back extension in order to leave the front of the house intact. This means your old timber windows have even more work to do to keep the home insulated.


Even more of a mess – when you combine poor insulation with a lot of south facing windows, you have a recipe for thermal and acoustic insulation disaster. Single glaze heritage windows simply can’t stand up to the job.


As part of the Thermawood process, a window professional will come to the property and evaluate each and every window’s needs, strengths and vulnerabilities with you.

  • Are there any drafts?
  • Do the windows still operate properly or will any refurbishing need to take place?
  • Can the existing hardware be used?
  • Is there any rot or evidence of water penetration?
  • What type of noise pollution is present and at what decibel and frequency levels?


By assessing the unique needs of the windows in each area of your home – for example, some rooms will need more noise reduction, others are more vulnerable to overheating in the summer – it’s possible to create a tailored double glazing solution for each window or room.


Features like argon gas, which increases the insulating power of your double glazed windows, low-E glass to repel more of the summer sun’s unwanted heat energy, and laminated or special acoustic grade glass to serve as a stronger sound barrier, can all be integrated within the same unit. This makes it possible to get precise results for each space in your home. You’ll also save money by not using features unnecessary for other windows in your home. 




Which means, you’ll get a complete, long-term solution, perfectly tailored to work for your property.


This is, after all, the ultimate objective. Double glazing usually comes with a 10-year warranty. Thermawood is all about longevity making your newly retrofitted windows last as long as possible.


With Thermawood’s specialised process and unique tooling – methods developed by people who have been in the industry for 30 years or more – your heritage windows should last for another hundred years.


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