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When it comes to restoring and insulating your heritage windows so you can enjoy the benefits of high-performance windows, just any double glazing system won’t work. 


If you don’t work with the right heritage window specialists, you could end up with aesthetic, functional and quality issues.


In other words, you’ll have an expensive mess on your hands.


This is what you should expect from your double-glazed heritage windows when you have them retrofitted:

  • Well-insulated windows that keep out the cold in the winter and solve your summer overheating problems;


  • Lowered energy bills;


  • A significant drop in noise pollution;


  • Beautiful windows that look and move like they did when they were built a century ago; and


  • Draft seals installed into all opening windows and doors that are machined into the timber.


If you don’t get these results, you may have to hire a second window company to fix the poor installation work the first company did.


The scary part is, if you don’t fix subpar workmanship, you aren’t just looking at problems like the lost charm of your original windows, double hung windows that don’t move smoothly or casement windows with extra drafts. Depending on how the windows were sealed, your insulated glass units (IGUs) may fail in a few years, forcing you to have to start all over again if you are beyond the typical ten-year warranty for double glazing.


Forget ten years. With the right heritage window specialists, there is no reason why you can’t get another century out of your property’s windows.


It pays to do your research and find experienced, skilled specialists for your heritage sash or casement windows from the beginning. These are the traits you should look for when searching for the right window specialists to work on your heritage windows.



1. Provide a Different Double Glazing Solution for Each Room


Your heritage property doesn’t require the same IGUs in every window in your home – each room will likely have a specific problem set and a specific set of IGU requirements to achieve the best results. 


For example, some of your insulating glass units will benefit from argon gas or special types of glass like acoustic-grade or low-E glass.



A hundred years ago, a lot of buildings were built back to front. As a result, your heritage home probably requires more thermal insulation in the front. You also may need acoustic grade glass in your double glazing for the rooms that face a noisy street – something that wasn’t factored in when your home was built a century and a half ago! Depending on the climates and which direction your windows face, you may also need low-E glass to combat overheating.


Solution-oriented specialists are going to focus on achieving the best results possible for your property. This means, tailoring your IGUs to suit the specific needs of each room of your house, giving you more insulation where you need it and not overdoing it where ‘more’ is just more expensive. 


This type of approach results in more effective double glazing for heritage homes, and a lower cost for you.



2. Have a Solution for Your Heritage Window’s Biggest Threat – Moisture


Probably the most critical distinguishing feature you want to look for is good drainage.


Moisture – from water vapour and the environment – will slowly rot your wooden frame. Water can also damage your window sealing, causing the interior of your IGUs to fog up and setting off a cascading effect of negative problems that lead to a failed double glazed unit.


The condensation on your glass will drip down, pooling around the bottom of the unit and speeding up the inevitable failure of the double glazing, as well as ruining your prized heritage timber frame. Your old Victorian or Edwardian window joinery is likely made from old growth timber – something you don’t want to have to give up and replace.


Old growth timber was frequently used a century ago when your windows were manufactured, and is incomparable in strength and durability to the timber used to make windows today.


Well-acquainted with the realities of what water can do to ruin windows (we are often the ones who are called in to restore windows that other double glazing companies have botched), a few years ago, we went to the drawing board to come up with a drainage system that would eliminate as much moisture as possible and stop water from damaging the double glazing and rotting the wood. 


Using 3-D printing until we got our design to work flawlessly, we created the only drainage system on the market effective enough to end the moisture problem of double glazed windows once and for all.



3. Use a Seal that Won’t Lead to a Failed Double Glazing System


Combine Thermawood’s specialised patented drainage system with our innovative approach to seals, and you have heritage windows, retrofitted to last through the ages.




When looking for window specialists, make sure you find out what they are using to seal the windows.


A lot of companies use silicon to seal around the beading and glass, and also around the IGU. The problem with this method is paint doesn’t stick to silicon and if the timber moves and a small gap opens, water will get into the rebate around the IGU and the frame will rot and the IGU will fail.


At Thermawood, we don’t use silicon, we use high grade Santoprene (high grade rubber) seals in the back of the rebate and on the outside beading so no non-compliant silicon will ever come in contact with the IGU. If any water does get into the rebate around the IGU it can easily drain away from the IGU and outside of the frame.



4. Restore and Refurbish Every Possible Feature for a Seamless Heritage Aesthetic


Something a lot of heritage property owners don’t realise is that they should expect their window specialists to restore every part of the window. Retrofitting is step one – it allows you to maintain your current timber frame but still have high performance double-glazed windows.


With heritage windows, there’s a lot more to be done.

  • Heritage hardware needs to be restored or replaced, if broken, with heritage-quality pieces.


  • Rotted or soft pieces of the joinery that can be refurbished should be.


  • Movement and function should be restored by your heritage sash window specialists – a lot of double hung windows no longer work correctly because they’ve been painted shut.


  • If you have lead lights, they should be professionally restored and then re-installed, within the double glazing where the heritage glass can be safely preserved.


  • With casement windows, any movement of the building structure over time has to be accounted for to prevent drafts when your double glazing is installed.


  • Sashes need to be re-weighted.


Are your window installers going to do all of this as a normal part of their service? 


If their goal is the genuine preservation of Australia’s heritage windows, they will in a heartbeat.


Thermawood takes care of every nuance of heritage windows to ensure they look exactly like original period windows; they just function as energy-efficient, high-performance modern windows.



5. Are Sanctioned by Heritage


And finally, if you want to know if you can count on your heritage window specialists, make sure they are approved by Heritage. You can rest assured your windows are in good hands when you’re relying on window specialists who Heritage councils trust.


Thermawood franchisees have been approved for Grade 1 and State-Listed properties, and we work directly with Heritage architects and councils to make sure Australian heritage homeowners know what is possible today to help preserve heritage windows.

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