Double Glazing Explained

Double Glazing Explained

What is WEERS?

WEERS is New Zealand’s “Window Energy Efficiency Rating System”.
The Window Association (now known as Window & Glass Association) has introduced a system called WEERS – which is an accurate rating of the energy efficiency of the actual window or door you purchase.

“The windows and doors you purchase are built to your exact requirements. The choices you make can change the energy efficiency rating.”

WEERS is Different to Other Window Energy Rating Programmes

WEERS is an advanced window energy rating system that offers you an accurate rating specific to each window and door that you purchase. Even if you buy two similar windows that are only slightly different, each one will have its own unique and accurate rating.

There are other window rating systems worldwide. Many of those are based on rating a standard window size and configuration, which may be quite different to the window actually being purchased, meaning that the customer does not usually know the actual energy performance of the window purchased.

When you purchase a house lot of windows the window manufacturer will be able to provide you an R-value for the entire house lot which can be given to your Architect or Energy Consultant to use in whole house energy calculations.

WEERS – The Technical Story

WEERS was developed by BRANZ in conjunction with the Window Association of New Zealand. EECA and MBIE have also been partners in the development.

WEERS energy rates all types of windows and doors. The rating takes into account the actual materials that make up the construction i.e. the frame material, the various glass used in the double glazing (insulating glass units) and the specific combinations of components associated with these.

The WEERS Rating Process

WEERS combines the thermal performance of all the frame components, the glass and the glazing method, also incorporating the configuration and size of the individual window to determine the thermal performance of the complete window as an R value, and also as a WEERS star rating. The WEERS rating process determines which high thermal-performance windows qualify for Energy Star endorsement.

Software performs the calculations as each window is being quoted. Each component part has its own unique data. The software has been verified as complying with the requirements of international thermal modelling standards, and the WEERS processes are audited annually.


Before being WEERS rated, windows and doors must meet the WANZ requirements which include compliance with the New Zealand Building Code including B1 Structure, B2 Durability, and E2 External Moisture; NZS4211 Specification for the Performance of Windows; NZS4223 for glass selection and glazing, and IGUMA-EN1279 for testing insulating glass units.

Overseas Ratings

WEERS ratings are specific to the New Zealand climate using New Zealand climate conditions as determined by BRANZ and MBIE.

Thermal efficiency ratings from other countries, including Australia, USA, Canada and Europe are not easily comparable for New Zealand conditions. It requires specialist expertise, such as that provided by BRANZ, to determine the reliability of any overseas energy performance claim if they are to be applied for use in New Zealand.

Any other performance claim for windows or doors, such as equivalency to NZS4211, or NZS4223 must be independently verified before being accepted for use in New Zealand. WANZ can facilitate such independent verification.

Whatever your double glazing needs are, you can be confident that we will provide the right retroGLAZE solution for your home

Explore our retroGLAZE® solutions

Timber Retrofit

Retain the character & superior insulating properties of timber, upgraded with high performing double glazing.

Aluminium Retrofit

Upgrade your existing single glazed aluminium windows & doors to high performing double glazing.

Replacement windows with new double glazing

Replacement Windows

Refresh and modernise your home with new high performance windows and doors