Until recently, professional sash window preservation wasn’t able to achieve the results modern heritage property owners have been looking for – beautiful, easy-to-operate historic windows that offer the original heritage aesthetic but work like 21st-century high-performance windows.

But now...

Thanks to new advancements in window technology, combined with a meticulous approach to older windows that focuses on longevity, it’s possible to not just restore these century-old windows but to set them up so they can last another hundred years.

Here’s the thing.

Sash windows aren’t just attractive. They represent an important piece of architectural history.

First put into use in the 18th century, single hung and double hung sash windows became a staple in buildings and homes across Australia. As such, they’ve become associated with classic periods, embodying more than historical charm but also the craftsmanship, style, and culture of an era.

It is for this reason sash windows are so highly valued today and why there’s such an effort to maintain them as much as is possible. In an effort to evolve the standard solutions for heritage sash windows, you’ll find that some window companies have started using new techniques.

In the case of Thermawood, we’ve gone so far as to design our own solutions, recognising the need for more sustainable and effective sash window restoration techniques.

Take a look at these four advancements, which are capable of offering a complete restoration system that can sustain your heritage sash windows for decades longer than what you'll get from the standard preservation process.

Retrofit Double Glazing for Your Sash Windows

To get the insulation benefits of double glazing and to preserve your existing timber windows, retrofit double glazing offers the most sensible solution. With retrofitting, your current timber joinery remains in place.

Thermawood rebate the existing sash and create a 15 degree slope on the bottom rail. This 15 degree slope houses the patented Thermawood drainage system which allows any moisture from condensation build-up on the glass to drain before it can pool around the base of the window and rot the wood.

Then, a double glazed insulated glass unit, or IGU, is installed where the single pane of glass was removed. Thermawood will also re-weight the sash weights to ensure the sashes are easy to move.

This leaves the original aesthetic of your sash windows intact, yet upgrades the windows for energy efficiency and acoustic performance, offering a more comfortable, quieter, eco-friendly home and increasing your property value. It also is the first step in protecting your windows from rotting and decay from water damage, which is your sash windows' greatest threat.

Patented Dry Glazing Drainage System

What makes Thermawood unique when it comes to retrofitting old windows with double glazing is that we’re obsessed with longevity. 

We know the quality of materials and level of craftsmanship that went into your double hung or single hung sash windows in the first place – and we also know, if they are properly restored and cared for, just how capable they are of outlasting even the new, modern windows being installed today.

So, we created a special dry glazing drainage system in order to maximise drainage and evaporation and to protect both the timber joinery and the double glazing units from the inevitable deterioration that comes with moisture exposure.

In addition to creating a slope during the retrofit process, we used 3-D printing to develop a system that would facilitate total drainage. This patented dry glazing drainage system means that even if water were to get into the rebate around your window, it won’t be able to do any damage because it will quickly drain away or evaporate.

Unfortunately, without this level of optimized drainage, your wooden windows are still susceptible to rot and decay. So, even if you have sash window preservation work done, you’re still looking at future water damage and the need for even more restoration work or a full window replacement.

High-Grade Window Sealing

One of the most important steps to preserving your sash windows is sealing. The problem with conventional silicone sealing is that the material is prone to cracks and small gaps, which can allow water to get into the rebate around your insulating glass units, causing the frame to rot and the double glazing to eventually fail.

To solve this problem, Thermawood uses the newer, high-grade synthetic rubber, Santoprene.

This material is resistant to not just water, but also to UV light, heat, and chemical exposure, offering far greater durability and protection for your windows. We use Santoprene seals in the rebate as well as the outside beading.

Sustainable Approach to Sash Window Preservation

And finally, the key ingredient to ensuring optimal longevity is mindset. A lot of window companies will settle for ‘good enough’ – if the window operates and doesn’t have any broken pieces, it’s good to go, right?

Not exactly.

There’s much more to truly preserving the integrity of old sash windows. We look at every nuance, from the hardware to the condition of the sashes and the frame to ensure the window system as a whole is set up to last.

This includes:

• Removing all the layers of old paint to get the sashes to move properly and to restore the clarity of the original window detailing
• Replacing broken hardware and cords with heritage-grade pieces
• Re-weighting the sashes so they operate even better than before we came
• Evaluating the state of the timber and restoring where necessary, even removing the sashes to have them professionally restored
• Identifying signs of excessive moisture and ensuring no rotted wood or vulnerable areas are left behind

When we’re done, your sash windows will look and operate like they did the day your home was first built. But, you’ll have a high-performance, patented dry glazing system in place to preserve the quality of your sash windows – and your home – for another lifetime.