What should I be asking when considering retrofit double glazing?

Retrofitting double glazing should be carried out by a skilled professional who can ensure that appropriate Building and Glazing Standards are followed in completing the work for you. Here are some things to check in advance of approving the work:

Is it genuine double glazing?

Ask them to explain the process and ensure that you are getting genuine double glazing.

What will your windows and doors look like when they have been double glazed?

Ask to see the changes in place so that you can check first-hand if the glass area will change and the overall aesthetics. Most windows should have no reduction in viewable glass area. Some doors (e.g. sliding doors) may have a small change. The finished outcome should be one where the changes maintain or enhance your home’s appearance – and don’t just look like an add-on.

What is the width of the space between the two pieces of glass in the double glazing unit?

This should be at least 10mm and not more than 16mm (the optimal space for double glazing is close to 15mm, depending on the glass and fill chosen). If the space is too small, the cold will more easily travel through the double glazing from one side to the other. If the space is too large, then convection currents are set up inside the double glazing resulting in reduced thermal performance. A 12mm space provides 8% better thermal performance than an 8mm space.

(Your double glazing will be there a long time, and 8% adds up to be a very significant difference over time!)

Is the spacer a high performance, thermal spacer?

‘High Performance’ double glazing encompasses thermal insulating performance and durability and a high-quality thermal spacer is a critical part of the thermal performance, particularly at the edge of the double glazing.

This is important for both timber and aluminium frames and will make a noticeable difference for condensation reduction.

What are the options available that can help address other issues at the same time?

Consider options for improved sound control, reducing fading and enhancing security.  Also, consider weather seals and new hardware options that could help improve your comfort and enjoyment of your windows.

What is the warranty being offered – on the double glazing and on the workmanship?

Double glazing manufactured by members of the Insulating Glazing Unit Manufacturers Association (IGUMA) has to meet BRANZ tested standards and comes with a 10-year warranty.

How long has the company been doing this work (retrofitting double glazing) and are they members of the Window and Glass Association of New Zealand (WGANZ)?

WGANZ membership provides you with an assurance of industry standards being met with quality workmanship and good service. Previous customers can also be a great reference for the quality of work and service that you can expect to receive.