Retrofit double glazing for existing timber windows and doors
Quality existing timber windows and doors can often be upgraded with double glazing. Thermawood retrofit double glazing allows us to retain much of the serviceable original timber joinery while upgrading the glass to improve thermal performance and comfort. It's particularly well suited to villas, bungalows, heritage properties and older buildings where the original timber windows and doors contribute to the architecture and character of the property.
Cedarlite specialises in timber joinery as well as retrofit double glazing, so we can look at the condition of your existing windows and doors before recommending whether they should be retained, require some work or would be better replaced.
Talk to Cedarlite about your property and we'll help you find the right way to combine the character of timber joinery with the benefits of modern double glazing.
Thermawood – double glazing designed specifically for timber joinery
Cedarlite uses the Thermawood system for our retrofit double glazing. Rather than being a generic glazing method adapted to timber, Thermawood is a patented dry-glazing system developed specifically for timber windows and doors.
An important part of the system is how it manages moisture. The timber rebate is created with the required slope and incorporates drainage components and seals, allowing moisture to drain and ventilate away from the edge of the insulated glass unit rather than remaining trapped within the glazing rebate. Specially designed timber glazing beads are then fitted as part of the completed system.
Thermawood is also the glazing system we use when manufacturing our new double-glazed timber windows and doors, giving us a consistent approach whether we're working with existing joinery or creating something completely new. You can read more about the Thermawood system here.
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Page: Double glazing wood windows Auckland | Retrofit timber windows NZ - Last updated: 20th October, 2026
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- Thermawood double glazing for new and existing timber windows and doors
- Glazing options tailored to thermal, acoustic, safety and privacy needs
- Refurbishment of existing joinery if possible and full window replacement if needed
Based in Auckland, we work on projects throughout New Zealand and welcome international enquiries.
Why retrofit your existing timber windows?
Cedarlite uses the Thermawood system for our retrofit double glazing. Rather than being a generic glazing method adapted to timber, Thermawood is a patented dry-glazing system developed specifically for timber windows and doors.
An important part of the system is how it manages moisture. The timber rebate is created with the required slope and incorporates drainage components and seals, allowing moisture to drain and ventilate away from the edge of the insulated glass unit rather than remaining trapped within the glazing rebate. Specially designed timber glazing beads are then fitted as part of the completed system.
Thermawood is also the glazing system we use when manufacturing our new double-glazed timber windows and doors, giving us a consistent approach whether we're working with existing joinery or creating something completely new. You can read more about the Thermawood system here.
The process of retrofitting double glazing
Depending on the window or door, the work can include:
- Removing the original single glazing
- Carefully machining the existing sash or frame
- Creating the required slope and drainage path
- Installing the Thermawood drainage and sealing system
- Installing a new insulated glass unit
- Fitting new timber glazing beads
- Installing draught or acoustic seals where appropriate
- Repairing localised areas of timber where agreed
- Adjusting or upgrading hardware where required
The aim is to upgrade the glazing while retaining as much of the serviceable original timber joinery as practical.
Choose the glass for the performance needed
Double glazing isn't one standard product. The glass can be specified according to the location of the property and what you want to achieve in different areas of the building.
Options can include:
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Standard double glazin
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Low-E energy-efficient glass
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Toughened or laminated safety glass
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Acoustic glass
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Privacy and obscure glass
- Tinted glass
For example, Low-E glass can be considered where improved thermal performance is a priority, while an appropriate acoustic specification may be useful for properties affected by traffic or other external noise. Safety, privacy and solar gain can also influence the glass selected. We'll help you work through the options rather than expecting you to know which glass specification you need.
When replacement timber windows may be the better option
Before retrofit double glazing, we assess the existing joinery to make sure it can properly accommodate the new insulated glass units. This includes the condition of the timber, sash dimensions, hardware, available clearances and structural capacity.
Localised areas of deterioration can sometimes be repaired as part of the retrofit work. However, if the timber is severely deteriorated or the existing joinery isn't suitable for the additional requirements of double glazing, replacement may provide a better long-term solution.
Cedarlite can manufacture new timber windows or doors and use the Thermawood glazing system, with new hardware and seals incorporated where required. For heritage and character properties, we can replicate original profiles, mouldings and detailing so the replacement joinery remains in keeping with the building.
Because we're timber joiners as well as retrofit double-glazing specialists, we can assess each window or door individually and recommend whether retrofitting, localised repair or replacement is the most appropriate approach.
What to expect from double glazing
Double glazing improves the performance of the glazed area of a window or door, but it's important to look at it as one part of the performance of the whole building. It can reduce heat loss through the glass and reduce condensation forming on the glass, but it won't address every possible source of heat loss, moisture or draughts within a property. The condition of the surrounding joinery (if the existing frames were kept) and the wider building will also influence the result. We can give you a realistic understanding of what retrofit double glazing can achieve for your property.
Many timber sash and double-hung windows can be suitable for retrofit double glazing. Their dimensions, condition, clearances, hardware and ability to accommodate the new glass need to be assessed before we can confirm this.
Yes, suitable existing glazed timber doors can also be upgraded using the Thermawood system. As with windows, we'll first need to determine whether the existing joinery is suitable.
This will depend on the number, style and condition of your windows and whether any additional timber or hardware work is required. We can discuss the expected timeframe once we've assessed the joinery and scope of the project.