What does double glazing cost?

Written by

12 May 2024


5 min read

Here’s what you need to know about retrofitting your existing windows with double glazing, or installing new ones.

Homes across Aotearoa New Zealand are often cold and damp due to poor insulation. One of the first steps to improving this is to replace single glazing with double glazing. This is an effective way of reducing significant heat loss, stopping cold penetration and therefore reducing condensation on the window areas, resulting in drier windows with less mould and mildew.

“Kiwi Double Glazing’s units are manufactured to the highest of standards using warm edge technology (non-conductive spacer bar) and Argon gas within the two panes of glass as our standard Insulated Glass Unit (IGU),” says Scott Cutler, director at Kiwi Double Glazing. “For high performing units, KDG offers Low E Units (Low Emissive Glass coating). These units reduce heat loss by up to 80 per cent as well as reducing heat gain in the summer down to 37 per cent from single glazing that is nearly 90 per cent.”

This technology is now standard for all new homes and full replacement joinery can be installed into your home when retrofitting into your existing frames.

Experienced in retrofitting double glazing – including insert frames, retaining the character of timber windows while upgrading them to perform as new – as well as manufacturing new thermally broken double-glazed windows, Kiwi Double Glazing offers options for existing and new homes that meet the H1 regulations.

Kiwi Double Glazing can retain the character of timber windows while upgrading them to provide better insulation.

The benefits of double glazing

“Kiwi homes are notoriously cold and difficult to heat because of poor insulation. It means that when people are trying to heat the whole house because of poor insulation and single pane glass, they close doors and really only live in one room and heat that room which then creates very cold and damp bedrooms, in particular,” says Cutler.

“With double glazing, mould and bacteria won’t build up around the frames, so it’s a huge advantage for health. By improving insulation throughout the home, you can allow all of the internal doors to remain open to allow more airflow and create a much healthier home.”

As well as keeping your home warm, dry and healthy, double glazing has numerous other benefits including noise reduction and ultraviolet protection, which lowers the effects of fading and damage caused to furniture and flooring.

Depending on your home and budget, Kiwi Double Glazing has various double glazing products to choose from (with performance varying depending on existing joinery):

Heat loss reduction

  • KDG Standard 56 per cent
  • KDG Ultra Clear Low E 80 per cent
  • KDG 4 Seasons Low E 83 per cent (with reduction of heat gain in summer to 37 per cent)

Noise reduction

  • KDG Standard double glazing will achieve around 10 per cent perceived sound reduction (PSR)
  • KDG 6.38mm Laminate double glazing achieves 35 per cent PSR
  • KDG 6.7mm Quiet glass incorporates an acoustic grade interlayer to achieve 50 per cent PSR 

UV fade reduction

  • KDG Standard double glazing will eliminate 42 per cent of UV entering through the glass
  • KDG Planibel Clear Low E will eliminate 50 per cent of UV
  • KDG 4 Season’s Low E double glazing will eliminate 80 per cent of UV
  • KDG 6.38mm Laminate will eliminate 99 per cent of UV
With a wealth of knowledge and many years of experience, Kiwi Double Glazing can take you through the process of creating a comfortable, healthy home for you and your family.

Limitations when retrofitting older windows with double glazing

“Retrofit is a great option because all the moving parts are replaced with new ones. There are few limitations except for the fact that sometimes the framing just isn’t suitable – it could be too old, too thin and it can’t hold double casing very well,” says Cutler. “What we would consider too old is generally anything from mid to late 80s.”

When retrofitting into timber, the original character of an older home’s windows can be retained. 

For example, this beautifully renovated Titirangi villa utilised Kiwi Double Glazing’s Heritage Windows to improve insulation while retaining the original charm of the home.

When retrofitting, the original character of an older home’s windows can be retained. 

Kiwi Double Glazing installed 10 purpose-made Heritage Windows into the original timber sub-frames, and the client decided to retain the upper single-glazed leaded light windows.

“The issue with timber windows is that people like the look of timber, but to upgrade them with double glazing you need to route out the existing timber which we don't recommend. What we offer is an aluminium insert frame – the Heritage Window – which looks very similar to timber, but then will hold the double glazing in a new frame. This allows the double glazing to be held correctly and it also means you can warranty the work,” says Cutler.

“Retrofitting double-glazed may not be suitable for all customers. If so, Kiwi Double Glazing offers a service of full replacement, providing windows that fully comply with the new and current H1 building code. Effectively, the H1 new frames have dense polymer in the frame separating the external and internal surfaces of the aluminium. This hugely reduces the conduction of cold and heat across the frame. This is known as thermally broken joinery.”

Kiwi Double Glazing also offers full window replacement with double-glazed windows that meet H1 requirements.

How much does double glazing cost for retrofits?

However, many existing windows are suitable for retrofitting and this is a great option for upgrading your home. Retro-fitting is a cost-effective option and Kiwi Double Glazing makes it easy to find out how much it will cost. 

“The cost of retrofitting your existing windows is a huge advantage, it’s considerably cheaper than full replacement,” says Cutler. “It’s a very quick, clean process; we often do retrofits in homes that are finished and decorated and have been lived in for years, but the actual process is very clean. It means less disturbance and what you achieve at the end is a high performing window with glass specification that meets new requirements.”

Although nearly all existing frames won’t be thermally broken, Kiwi Double Glazing can offer thermally broken sashes.

Kiwi Double Glazing’s online quote calculator provides cost estimates based on standard double glazing – with additional cost for Low E and noise reduction products.

Explore projects on ArchiPro that have used Kiwi Double Glazing and get in touch with the team to learn more about retrofitting or building new windows for your home.