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When you know how to protect your wooden windows from rot, there’s no reason why your prized heritage windows can’t last another century. 


One of the most common misconceptions surrounding timber windows is that they are going to eventually succumb to rot and start to fall apart. 


In truth, the old growth timber that was probably used for your windows is one of the most durable – and beautiful – building materials on earth. You just need to know how to look after your wooden windows in order to preserve it. 


Depending on the workmanship involved in installing your original windows or any restoration work that’s been done over the years, it is true that your windows may be vulnerable to moisture. This doesn’t mean they’re doomed. Their longevity all depends on the window system you have in place.


Upgrade the system, no more worrying about rotten timber frames.


No matter what hardwood window maintenance you have done, such as restoring soft pieces or applying a wood preservative, if the window system itself isn’t designed to promote maximum drainage and evaporation, you’re still looking at a problem once your timber frames are exposed to enough water. 


Here’s what you need to know about protecting your wooden window frames and preventing rot. 



Water Will Damage Your Windows 


Water is your wooden window’s biggest threat. It can damage the frame, lead to cracks through which heat can escape, and can encourage serious problems like mould growth and poor indoor air quality. 


  • Water causes wood fibres to expand, softening the wood. 


  • Once you have a moist surface, the timber frames are more vulnerable to mould growth and insects. 


  • Saturated water vapour can damage your window’s silicone sealing, leading to a host of problems like pooled water and drafts. 


You can’t stop water from getting in your windows. It’s not just rain that you are dealing with, but water vapour in the air, both outside and inside your home. When your glass is cold, which is a chronic problem with single glazed windows, water droplets form on the surface of the glass, drip down, and pool around your frames.




What you can do is make sure it is draining as fast as possible. Which is what Thermawood did when we created our patented drainage system for retrofitting timber windows



The Solution for Protecting Wooden Windows from Rot 


The heart of Thermawood’s Retrofit Double Glazing solution is the patented drainage system. It was created specifically to deal with the moisture issues that other double glazing systems create and that single glazed windows, by nature, have. 


The first problem a lot of homeowners don’t realise is that when you double glaze your heritage windows, the seal installers use around the insulating glass units will eventually break. As a result, moisture fogs up on the inside of the glass. Then, you end up with water sitting at the base of the window and will need to replace the double glazing. Keep in mind, most double glazing warranties last for only 10 years. 


Problem two – the water has nowhere to go. This means the timber frame is sitting in water. 


So, we came up with a system to ensure the double glazing won’t fail and can preserve the original wooden window frames for another 100 years. 


  • We use a unique, patented drainage system, which sits beneath the double glazing. This way, any water that gets in the glazing rebate will immediately drain out. We used 3-D printing to create working models until we were confident the design would work as expected, even in old casement and double-hung windows. 


  • Silicone blocks are used to support the double glazing on a 15-degree angle; there are no seals or silicones that can touch the insulated glass unit and potentially damage the polysulphide seal.





Protecting Wooden Window Frames and Updating Their Performance 


If you have your original single glaze heritage windows, you may be facing a long list of issues: 

  • Poor insulation and high energy bills; 


  • No protection against noise pollution; 


  • The timber frames have soft, worn areas and are in dire need of refurbishment; and


  • No idea how to solve all of these problems without ruining the look and movement of your old wooden windows. 


By retrofitting double glazing, you can update your windows so they offer 21st-century performance and have all your problems solved with one solution. 


Thermawood makes a 15-degree slope in your current heritage window frames to install the drainage system and high-performance insulating glass unit (two panes of glass separated by a sealed air space) in place of your single glaze. 


This means you retain the aesthetic quality and charm of your heritage windows without even knowing we have been there but enjoy the warmth, comfort, and quiet of well-insulated windows. 


While also eliminating all the issues that can cause you wooden window frames to rot!


We also can address any issues your heritage windows have. 


  • Any worn wood we can refurbish. 


  • Broken hardware, we can replace with heritage quality pieces.


We’ll even make sure they function like they did when they were first installed – we machine the seal into the timber so when we retrofit your windows we eliminate any gaps from where the building has settled around the window sash, a common problem with old casement windows. 


A lot of heritage homeowners with double-hung windows can’t move the top sash because it’s broken or has been painted shut for decades. We remove any paint, repair any broken parts and have century-old double-hung windows operating flawlessly. 


But, most importantly for the longevity of your windows, you’re protecting your wooden window frames from water damage when they are refurbished with Thermawood’s patented drainage system. 



Looking after Wooden Windows Over Time 


It’s also important to practice general wooden window frame maintenance. Timber has natural preservatives, which can be brought out by oiling or waxing the wood. You can also use a paint, varnish, or special chemical wood preservative for window frames. 




Keep an eye on your windows. If you notice the wood starts to look warped or feels soft, or if it doesn’t move easily or you notice drafts, have a professional take a look. These could be signs that you have a larger problem developing. By taking care of small issues early on, you can prevent big issues like rot, mould, and a broken system, from ever developing.



Making Sure Your Wooden Frames Last a Lifetime


Don’t give up on your heritage windows. 


The way windows were made over a century ago is different to how they are built and installed today. The level of workmanship, the materials – everything was intended to stand the test of time. 


By updating your windows with the same level of workmanship and care, as well as the latest advancement in window technology, you can protect your wooden frames, update your windows’ performance, and enjoy the character and charm that makes heritage windows so highly valued today. 

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