embodied carbon. Aukland CBD buildings people walking
Photo: Tanay Vora

Steel and concrete are New Zealand’s worst offenders when it comes to embodied carbon, together contributing more than half the carbon footprint of both residential and non-residential construction, according to a new report.

Commissioned by the New Zealand Green Building Council (NZGBC), the report also found aluminium is a “very significant” source of green house gas (GHG) emissions in the industrial and commercial sectors.

Timber framing is the third biggest contributor in residential construction, followed by paint, aluminium and plasterboard.

The report, written by thinkstep, a building sustainability consultant, found that the amount of greenhouse gas emissions from new-build construction and renovation in New Zealand is equivalent to that from one million cars or more on the road every year.

The report will inform part of NZGBC’s submission to a parliamentary select committee on 19 August that will examine the New Zealand government’s Zero Carbon Bill.

The report measures the carbon emissions created through the supply chain when building products are made (known as embodied carbon) on a national level.

The report also looked at short and long-term solutions to the problem.

Tackling embodied carbon will be a collaborative effort. No one sector is to blame. But the report’s researchers hope that it’s possible to decarbonise 40 per cent the country’s embodied carbon footprint. This amounts to taking almost 15 per cent of the country’s cars off the road.

When it comes to detached houses, increasing the proportion of low-carbon concrete could reduce emissions by 5 per cent (3 tonnes of CO2e).

Longer-term changes to the way building materials are manufactured, such as powering the manufacture of cement with coal alternatives, could cut 29 per cent of GHG (18 tonnes CO2e).

Low-emission concrete and aluminium also has the potential to slash embodied emissions in the non-residential sector by as much as 19 per cent (85 tonnes of CO2e).

Improving how these key materials are manufactured could cut 51 per cent of emissions (230 tonnes CO2e) generated by non-residential buildings.

The report says specifiers and customers need to choose materials carefully, with an eye on their embedded emissions.

Government buildings can be a good place to start. The report recommends using a life cycle assessment, such as Green Star, when specifying government building programs, as well as embodied carbon considerations in public and private procurement policies.

It is essential the government take the lead on decarbonising NZ  buildings, said Andrew Eagles, head of the NZ Green Building Council.

“They can do this in two clear ways,” he said. “Firstly, by ensuring there’s a building expert on the Climate Change Commission. Secondly, as the largest and most significant building occupier in Aotearoa [New Zealand], the government can clean up their own house, and ensure that all their buildings are climate-friendly, clean and efficient places.

“We need to construct healthy, efficient buildings and warm, dry homes, and slash carbon emissions, too. And these go hand in hand.”

The researchers also recommend ensuring the NZ Emissions Trading Scheme accounts for the emissions embodied in imports.

Good-quality data can also help address embodied carbon. The recent publication of product carbon footprints and environmental product declarations (which include a figure for embodied carbon) for a number of New Zealand-made building products is making this easier.

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