Retrofit Double Glazing for existing Timber and Aluminium Windows and Doors

Retrofitting is the installation of double glazing fitted into existing aluminium and timber windows and doors.

As well as the huge benefits of double glazing, retrofitting into your existing joinery has its own advantages:

More cost effective than replacing existing windows with new window frames

  • Enables you to preserve leadlight windows 
  • Improve draught sealing 
  • Maintains and preserves the architectural integrity and character of your home
  • Environmentally positive by retaining perfectly sound existing aluminium or timber windows and door frames

Thermawood Retrofit Double Glazing System

The Thermawood Retrofit Double Glazing System has been designed specifically for existing timber windows and doors. Dunedin and Otago is renowned for its character homes, however the extreme weather conditions have identified them as draughty and cold. Double glazing provides protection from the cold, helping to abate some of perils of older homes. Many retrofit double glazing systems into Timber Joinery do not allow for adequate drainage required to withstand the local weather conditions. The Thermawood Retrofit Double Glazing System is the only system designed with this in mind. Using the Thermawood Retrofit Double Glazing System ensures the longevity of the double glazing and also retains the original look and character of a home or building.

Leadlight Preservation

Working with a well-respected local leadlight restorer, Thermawood Otago is able to repair and double glaze leadlight windows by replacing broken sections and recementing the lead where necessary. Double glazing leadlight windows preserves the original panels with all the added benefits of double glazing. The panel is removed, restored, then placed in-between a double glazed unit before being fitted back into the window opening.

Rot Repair

Traditionally glazed timber framed windows and doors can rot, especially when exposed to moisture for long periods of time. Rot can continue to spread even when the source of moisture has been eliminated. 

Our qualified timber joiners will assess any rot and discuss options for repair or replacement. 

The Thermawood Double Glazing System was designed to mitigate this and is the only Timber Retrofit double glazing system tested and approved by the New Zealand Standard Authority to allow any moisture around the double glazing to drain away freely. This protects your double glazing and timber frames from any future moisture retention, which can cause rot or breakdown of a double glazed unit. 

To ensure the longevity of your double glazing and their timber frames, speak to the timber retrofit double glazing experts - Thermawood Otago

Draught Sealing

Ill-fitting windows and doors are quite common, especially in timber joinery, which unfortunately creates draughty homes. Thermawood are able to remedy draughty windows and doors. We have different options to suit window and door types.

The draught sealing work is carried out by our tradesmen timber joiners, who will custom make and fit the suitable seal for your windows or doors. 

This is a very cost effective way to retain your heat and get the most out of your double glazing.

Retrofit Double Glazing FAQ's

Our most commonly asked questions about retrofitting

Q: Can my wooden windows be retrofitted?

A: In most cases yes, we complete a written assessment of your windows to make sure they are suitable to be retrofitted. A copy of this is available on request. We can retrofit casement, double hung and fixed windows.

Q: Can you install draft seals into the wooden window?

A: Yes we can install seals into all opening windows, including double hung windows to make them more efficient. We generally price the seals separately.

Q: I have double hung windows, will they stay up with the extra weight of double glazing?

A: Yes, we weigh the sash with the double glazing installed and re-weight the double hung windows accordingly so the still operate as they should.

Q: Do you remove the windows and take them to your workshop to do the work?

A: No, if possible we do all the work onsite. We remove the windows, rebate the frames and reinstall the windows the same day.

Q: How long will the job take?

A: When you are given your quote, you will also be given an indication of how long the job will take.

Q: Can we price per window?

A: Yes we can price per window or per room.

Q: Can we just retrofit one window or one room at a time?

A: Yes this is why we price per window or per room so you can retrofit your home within your own budget and timeframe. We have many customers that are on our installation schedule for 2-3 years progressively working around their home.

Q: Why should I use the Thermawood System?

A: The Thermawood Retrofit Double Glazing System is the only system that uses a drainage adapter under the double glazing to prevent any moisture sitting around the double glazing. Any moisture sitting around the double glazing will cause the double glazing to breakdown and fail over time. This breakdown becomes visible when the moisture starts to build up in-between the two panes of glass causing it to fog inside. This cannot be fixed, the whole double glazed unit will need replaced. The Thermawood system provides reassurance you will get longevity from your double glazing no matter what the conditions. (See our about & information pages for more info)

Q: Has the system been tested?

Yes the Thermawood System has been tested to New Zealand Standard 4211 and passed, which covers weather tightness and durability to very high wind zone. A copy of this test report is available on request.

Q: Will installing double glazing stop condensation?

A: Double glazing will help condensation, if your glass gets cold enough it will still condensate slightly but double glazing will help retain the heat in your home to reduce the condensation. You may now notice condensation on the outside of the windows, particularly on South facing windows.

Q: What are the products made from?

A: The Thermawood 'Grandadapter' is made locally from recycled milk bottles and all our timber beadings come from sustainable sources. The Thermawood system is environmentally sound which, is something we take great pride in.

Q: Will double glazing make my house quieter?

A: Yes, standard double glazing will make your house quieter by approximately 25% but if noise is a particular problem we can use different glass types in the double glazing to reduce the noise further to approximately 55%.

Q: Will double glazing make my house warmer/cooler

A: Double glazing will make your house warmer or cooler as long as you heat or cool the house, the double glazing will help retain the heat or cold in the building. Double glazing works just as well for keeping heat in as it does for keeping the cold in from air conditioning making it a year round solution for energy efficiency and savings.

Q: I have some leadlight windows, can I keep the leadlights.

A: Yes, the Thermawood system refurbishes and protects the leadlight by having installed a new border lead, resealing the leadlight and then installing the leadlight into a double glazed unit where it will remain preserved.

Q: Do you paint my windows after the job is complete.

A: Generally we don’t get involved in the painting as most people either like to paint their own windows or have their own painter. We will leave the window ready to be painted with all bare timber primed and the pin holes all filled and ready to be painted. We do have painters we recommend if needed.

Q: What if you find some rotten windows?

A: We complete an assessment of the windows when we quote the windows but sometimes rot is not visible until we rebate the windows.  If this happens we can arrange to have new replacement items made to match the existing and installed along with the rest of the job for a very competitive price. This is generally the only thing that would change our quoted price. 

Q: Can I keep my original hardware?

A: Yes, if your hardware is still in good workable condition and suitable for retrofitting, we will use it. We do have a large range of new hardware available to suit your home/existing hardware if needed.

Q: What are the benefits of incorporating Low E (Low Emissivity) and or Argon Gas?

A: These products increase the insulating performance of double glazed units. (See our product info) 


We are true experts in the field of retrofitting, please speak to us for more information.

03 4884000 71 Maclaggan Street, Dunedin

03 4454004 13 Hughes Crescent, Cromwell


©2017 Thermawood Otago Ltd