In late 2021 the New Zealand Building Code announced its biggest energy efficiency changes in over a decade, with the latest amendments requiring significant improvements to the insulation of the building envelope, including windows, and introducing six new climate zones to reflect specific weather in different areas of the country.
The changes aim to make new homes and buildings warmer, drier and healthier with less impact on the planet, and the continued improvements in window quality (among other things) are expected to reduce the energy required for people to heat their homes by up to 40%.
These building code improvements are in stark comparison to the minimum levels of energy efficiency legislated in the Australian National Construction Code (NCC), which already lagged behind New Zealand in terms of thermal performance and insulative requirements before these latest changes.
During 2021, the Vinyl Council of Australia made a submission on the public comment draft of the NCC 2022 supporting an increase to the minimum level of energy efficiency mandated in buildings and calling for maximum U-value thresholds and Solar Heat Gain coefficients for windows by climate zones.
This suggested focus on a need to improve the energy efficiency of windows in new buildings is based on the well-founded knowledge that windows are the single largest influence of heat loss and gain in Australian homes, which in turn has a direct effect on the amount of energy use required to control internal temperatures year-round. As the lower the value, the more insulative the window, setting a maximum U-value is one of the most simple and effective ways to drive improvement in the thermal envelope of buildings and is relatively simple to update over time or adjust in different climate zones.
The Vinyl Council’s submission called for a simplification of the approach and measurements in place to legislate maximum U values by climate zone, such as the standard set in the New Zealand Building Code. Currently, the Australian NCC includes pages of complicated tables and a glazing calculator which even if followed still allows scope for trade-offs in efficiency that see windows with U values of over 5 allowed to be used in climates such as Melbourne.
Jenni Tipler, Manager of Building Performance and Engineering at the Ministry of Business in New Zealand, is reported as saying that the recognition that “windows represent the largest source of heat loss in new homes” was a key driver for the changes in the New Zealand Building Code, which unlike its Australian equivalent, encourages use of higher thermally performing windows.
Changes made in the New Zealand Code include increasing the minimum insulation level for windows (as well as roofs, walls and floors) across the country, with a focus on targeted higher upgrades in colder climate zones. The new window insulation requirements in the warmest climate zones will see a 2-step approach with an interim increase in the next year and an additional increase in the following year, while all other parts of the country (climate zones 3, 4, 5 and 6) will have a 1-year transition period. By the end of 2023, all parts of the country will have a similar minimum level of window insulation requirements.
The simple, 2-step approach for the window insulation requirements is designed to allow the sector to prepare for the changes before they become mandatory for new builds. Under the 2021 updates, the maximum U-value of windows for New Zealand by climate zones are as follows:
The reluctance of Australia’s NCC to adequately regulate for an impactful increase in energy efficiency standards through means such as setting maximum U-values for windows will cause a substantial delay in allowing Australia to move towards net zero buildings, a trend seen in many other countries that have made a mainstream transition to higher performing windows such as uPVC.
The Vinyl Council’s uPVC Windows Alliance welcome the changes in New Zealand’s Building Code to regulate for higher performing windows and will continue to advocate for the Australian NCC to make the thermal performance of windows and the simple requirement to stipulate maximum U values a priority moving forward.
 It should be noted that New Zealand U values are based on European U value calculations, while Australia’s Window Energy Rating System (WERS) follows the American National Fenestration Rating Council (NFRC) system for calculating U values. However, Australian U values are given in the metric system (i.e W/m²K) rather than the US imperial system. European U values are calculated under a different methodology standard and would appear slightly lower than Australian values, even for an identical product.