Comparing the Waitakere NOW Home to other new builds

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Even though it was built over ten years earlier, the Waitakere NOW Home still outperforms most new houses being built today. 

BRANZ researcher Roman Jaques used the NOW Home as a benchmark to see how current new homes were performing.  He randomly selected over 200 building consents from Auckland, Hamilton and Christchurch and modelled their performance using the submitted specifications.  He compared this data to modelling of how the NOW Home would perform in the three locations.

Findings

Overall, he found that, compared to the NOW Home, the 2016 homes, with very rare exceptions, have:

1.     Considerably higher space heating and cooling-related CO2 emissions

The Y2016 homes (with a few exceptions) have considerably higher space heating and cooling loads and therefore CO2 emissions.

2.     Higher water heating-related CO2 emissions

There is a considerable gulf between a carbon-efficient water heating system and what is typically being installed. Comparing the mean figures, the NOW Home has approximately 3.5x, 3.4x and 2.7x less carbon-intensive water heating requirements for Auckland, Hamilton and Christchurch respectively

3.     Lower whole-house resource efficiencies, by bedroom number

Resource efficiency is calculated by simply dividing the conditioned area of a house by the number of bedrooms. The lower the number, the more efficient the house is likely to be. The NOW Home was designed specifically to address this issue; it forgoes hallways and has compact bedroom spaces.

4.     More energy-intensive space heating and cooling needs via active means

The difference between what could easily be achieved through considered design (i.e. the NOW Home) and what is currently being achieved (i.e. the randomly selected homes’ median performer) in terms of the level of active heating and cooling required is considerable. This gulf in thermal performance is even more startling when only a handful of selected homes designed for the Christchurch climate thermally outperform the NOW Home, which was designed for a considerably more clement climate.

5.     Less daytime thermal comfort in the main living area via passive means

Compared to the NOW Home, the Y2016 consented homes, with very rare exceptions, are considerably less comfortable via passive means (Christchurch result available only), having more extreme temperatures in the main living area.

6.     Fewer extreme temperatures in the main living area

Compared to the NOW Home, Christchurch new builds have considerably more overheating (defined as temperatures greater than 25°C) in a key area - the lounge. This suggests that randomly selected designs didn’t consider shading in a meaningful way.

The thermal performance of the NOW Home is considerably better in terms of limiting both uncomfortably hot and unhealthily low temperatures when using the main living space as a proxy for the whole house.

Conclusions

While this 2019 report found some improvements in new builds over an earlier benchmarking report in 2015, it concludes that the underperformance of new homes needs urgent attention.

“ ‘Where properly planned and used, our homes can be low-carbon, more comfortable to live in, better for our health, and more affordable to run’ (Committee on Climate Change, 2019). There is good evidence that newly built, detached New Zealand homes are far from well planned, based on those consented in 2016 in three key cities. This situation needs urgent remedying, especially if New Zealand wants significant progress in this area to meet its 2050 goals of being carbon neutral as well as generally improve new homes’ comfort, health and affordability….

The time for discussion is over.“

Jaques, R. (2019). Measuring our sustainability progress: New Zealand’s new detached residential housing stock (first update). BRANZ Study Report SR426. Judgeford, New Zealand: BRANZ Ltd.


  • 01-Nov-2019 (Report )

    Measuring our sustainability progress: New Zealand's new detached residential housing stock (2019 update) (PDF 2.2MB)

    Roman Jaques

    This is the second report of an ongoing longitudinal study on key sustainability-related aspects concerning new New Zealand detached housing consented in the 2016 calendar year. It covers a range of core indicators grouped into eight domains: energy and CO2, water, indoor environment, resilience, affordability, consumer demand, industry capacity and policy and regulation. It provides a breadth of information over three thematic areas: building performance, market forces and governance. Although a stand-alone document, its predecessor BRANZ Study Report SR342 should be read prior to or concurrent with this first update for best comprehension.


  • Find BRANZ’s other reports here