What is Thermawood and how does it work?
Thermawood is a patented retrofit double glazing system developed specifically for existing timber windows and doors.
Rather than removing the entire window and replacing it, the Thermawood system adapts your existing timber joinery so a modern insulated double-glazed unit can be fitted securely into it. The timber stays, the single glass is removed, and the window is carefully prepared for the new glazing system.
What makes Thermawood different is that it isn't simply about fitting thicker glass into an old frame. The system has been designed around how the new double glazing is supported, sealed and drained once it is installed.
Why was the Thermawood system developed?
The system was developed after seeing double-glazed units fail in timber windows because moisture had become trapped around the glass.
If water continually sits around the edge of a sealed double-glazed unit, it can eventually affect the seal. Once that seal fails, moisture can get between the two panes of glass and cause the familiar fogged appearance that can't simply be wiped away. The glass unit then needs to be replaced.
The thinking behind Thermawood was simple: If water gets into the glazing area, it needs somewhere to get out. That led to the development of Thermawood's patented drainage system.
created here in New ZEaland
Early development of the system took place around 2008, with the design taken to the business development unit at Otago Polytechnic, where the original CAD model was developed further. The system components are manufactured in New Zealand, and Thermawood's drainage adapter is made from recycled material. For Thermawood Otago, that's a particularly fitting connection.
The Thermawood system has been tested and approved to New Zealand Standard NZS4211:2008 for weather tightness.
A drainage system built into the window
When your existing single glazing is removed, Thermawood's purpose-designed tooling is used to carefully prepare the timber for the new double-glazed unit.
The base beneath the glazing is formed with a 15-degree slope, with the Thermawood drainage system sitting underneath the glass. If moisture gets into the glazing area, the slope directs it down to drainage points that allow the water to escape to the outside of the window. So rather than relying on the idea that water will never find its way into a window, Thermawood has been designed around what happens when it does.
Why does that matter?
Both timber and sealed double glazing perform better when water isn't allowed to remain trapped around them.
Thermawood's drainage system helps protect the edge of the insulated glass unit while also reducing the amount of moisture sitting against the surrounding timber. It is one of the key differences between the Thermawood system and simply making enough space in a timber frame to fit a double-glazed unit.
What does 'dry glazing' mean?
You'll often hear Thermawood described as a dry retrofit glazing system. This means that the double-glazed unit is installed as part of a purpose-designed system that supports the glass while allowing moisture to drain away, rather than leaving the unit sitting in an area where water can collect underneath it. The prepared timber, sloped base, drainage adapter, support system, seals and finished beading all work together around the new glass.
In other words, we're not simply squeezing a double-glazed unit into an existing timber window. We're converting that window so it is properly set up to accommodate modern double glazing.
Warm Edge technology around the glass
The two panes of glass in a double-glazed unit are held apart by a spacer that runs around the edge. Thermawood uses Warm Edge technology, with a high-performance spacer made from stainless steel and insulating plastic materials to reduce heat transfer through this area.
This helps improve the thermal performance of the complete double-glazed unit and reduces the likelihood of condensation forming around the colder edges of the glass.
You don't see any of this once your windows are finished, but it plays an important part in how efficiently the glazing performs.
the advantage of timber
Wood contains tiny air pockets within its cellular structure, making it a natural thermal insulator, while those same characteristics also help dampen acoustic vibrations.
Timber windows are naturally better insulators than aluminium, so rather than replacing them, the Thermawood system allows us to retain their insulating properties and improve the glazing within them.
Better performance without changing the character of your windows
The engineering behind Thermawood may be sophisticated, but you shouldn't notice it when the job is finished. Your existing timber frames remain in place, with only the timber needed to accommodate the new system carefully machined before new beading is fitted around the double-glazed unit.
The aim is to improve the performance of your windows without making them look like an obvious retrofit. That's particularly important for character and heritage windows. If any timber window restoration work is needed we can complete this at the same time. Retrofitting double glazed windows keeps the internal glass surface warmer, significantly reducing condensation on your windows.
Thermawood is the retrofit system rather than a particular brand of glass. This means different types of double-glazed units and glass can be installed within the Thermawood system depending on what you want to achieve.
IGU stands for Insulated Glass Unit, which is the technical name for the sealed double-glazed unit fitted into your window. It consists of two panes of glass separated by a gap that can contain air or an insulating gas such as argon.
Low-E stands for low emissivity. Low-E glass has a very thin, virtually invisible coating that helps reduce heat transfer through the window while still allowing natural light through. When used with double glazing, it helps keep more warmth inside your home during colder weather, improving the overall insulating performance of your windows.
Yes. The system can accommodate different glazing options, including Low-E glass for improved thermal performance and acoustic glass where reducing outside noise is a priority.
Argon is an inert gas that can be used to fill the space between the two panes of a double-glazed unit. Because it transfers heat less easily than ordinary air, it provides an extra layer of insulation, helping improve the overall thermal performance of your windows.
Argon gas can be combined with Low-E glass when you want a higher-performing glazing option.
No! The phrase "retrofit double glazing" simply means installing double-glazed units into existing window frames rather than replacing the complete windows. How those units are fitted, supported, sealed and protected from moisture can differ between systems.
Thermawood is a purpose-designed retrofit system for timber windows, with a patented drainage system that allows moisture entering the glazing area to drain away rather than remain trapped around the glass.
excellent in every regard
"Our experience dealing with Thermawood has been excellent in every regard. Prompt and efficient service, a high standard of workmanship and excellent communication and followup. Also they are really friendly and helpful to work with. I would give this company a top score."
Alistair Chalmers ( Owner - Arrowtown Engineering )