This is part 1 of a 3-part series on household emissions in NZ. This part looks at whole-of-life emissions from housing. Part 2 will do the same for household transport, and part 3 will tie them together (the implication being: it really matters where we build new homes).
Globally, we need to reduce greenhouse gas emissions by lots, and we don’t have very long to do it. New Zealand has its own targets and Heidi has written about Auckland’s C40 commitment to a 50% drop in emissions by 2030.
Here’s the Stats NZ breakdown for household consumption emissions, aka their annual “carbon footprint”. It includes ‘indirect’ emissions from the manufacturing process, e.g. clothing or cars that were made overseas but sold to NZ households.
Source: “Greenhouse gas emissions (consumption-based): Year ended 2017”, Stats NZ. I’ve added in emissions from the construction of housing, which are actually categorised as “gross fixed capital formation” of “residential buildings” rather than household consumption. I divided the aggregate figures by 1.721 million households to get the average per household.
Transport stands out pretty starkly as the biggest contributor, but today I’ll focus on “housing and household utilities”.
Some recent research looks at the whole-of-life emissions from a typical detached house. Since it includes the construction as well as the operation of the home, it’s conceptually similar to the ‘direct plus indirect’ emissions measured by Stats NZ.
The researchers assume the house has a 90-year lifetime and is almost 200 square metres in size, which is bigger than the average existing house but pretty typical for a new one. The total emissions from the house over its lifetime are shown in the graph below:
The “upfront” emissions from building the house add up to 42 tonnes before the house is lived in (although if you allow for ‘biogenic carbon’ in the wood used to make the house, then this reduces to around 21 tonnes). The ongoing energy and water use, plus maintenance and replacement, add up to 231 tonnes over 90 years or 2.6 tonnes per year.
Unsurprisingly, building the home is a big part of the emissions: equivalent to 16 years of energy use/ water use/ maintenance. If you group construction with maintenance and replacement, then they are equivalent to 36 years of energy and water use. Even so, that’s under 30% of the lifetime emissions, so energy efficiency is very important.
The research was covered in a Newsroom article titled “new houses emitting five times too much carbon” – that’s based on the authors comparing the figures above to what they thought the target should be, using a top-down global carbon budget based on 2°C of warming (which as Heidi’s article notes, isn’t exactly comfortable).
The Newsroom article also quotes the authors:
“There are things we can do quickly to get the carbon down,” says Dowdell. “The big one is the house size. There is a close relationship between house size and carbon footprint.”
“Then, making houses more energy efficient, especially in places like Wellington and further south. Orienting our houses so they get good winter sun and making sure there is shading in summer, using good high-spec double-glazed windows that are well installed. Simple things like that don’t add much to the cost. They cut the carbon, but typically we are not doing them in a routine way.”
The authors focused on detached houses and haven’t looked at apartments yet, but they plan to. They note “some trade-offs there, in that as we start to build higher, we use material with higher embodied carbon such as concrete or steel… But getting the size down and having higher density living also provides other carbon benefits in terms of allowing people to live in proximity to jobs and transport hubs”.
Building smaller homes is a key move. Beyond that, my takeaways from the research are the importance of cutting operational emissions for all homes (partly through design, as per the quote above), and choosing low-emissions products for new builds (wood is best).
Lastly, there’s a whole bunch of research from around the world showing that it’s much more efficient to upgrade old homes than to build new ones: for example, “it would take an average of 168 years for a high-efficiency home built in Vancouver today to “earn back” its embodied emissions”. In the UK, building a cottage involves 80 tonnes of emissions but upgrading an old one involves just 8 tonnes, and “even the highest-specification newbuild could not catch up this advantage over the 100-year period”.
Auckland is growing so we will certainly need new homes, but upgrading existing homes is also very important. More on that another time!