A new report claims the construction industry in New Zealand will emit as much carbon as 1 million cars every year from now until 2050.
But it's possible to reduce that by half, according to sustainability company thinkstep, which authored the report.
Green Building Council CEO Andrew Eagles says it is a serious situation.
"We're not going to meet our zero-carbon targets by 2050 unless we seriously go at this, and go even further than what we're setting out in this report."
The report, titled Under Construction: Hidden emissions and untapped potential of buildings for New Zealand’s 2050 zero carbon goal, suggests the construction industry belches out about 20 percent of the country's carbon emissions, but could slash 1.2-million tonnes every year - the equivalent of taking half-a-million cars off the road.
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Eagles says concrete is an example where materials could be substituted.
"They can use pozzalon, which is a natural material rather than cement that significantly reduces carbon emissions. With steel, you can change the beam design."
He does not believe the changes would significantly increase building costs.
"Nobody talks about it. It's not in the building code, it's not in the procurement rules for the Government. So we're creating all this carbon pollution, but we're not doing much about it."
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He hopes the report will help encourage the industry to act.
"They can do this in two clear ways. Firstly by ensuring there’s a building expert on the Climate Change Commission. Secondly, as the largest and most significant building occupier in Aotearoa the Government can clean up their own house, and ensure that all their buildings are climate-friendly, clean and efficient places."
New Zealand's greenhouse gas emissions increased 19 percent between 2007 and 2017, mostly due to transport and dairy farming.
Prime Minister Jacinda Ardern has called climate change the "biggest challenge facing the international community and New Zealand". Last week she was at the Pacific Islands Forum, where leaders of nations at risk of being submerged urged richer countries like New Zealand and Australia to do more.