Buildings could be belching out 20 per cent of New Zealand's carbon pollution - and much more needs to be done to make them greener.
That's according to a new report by sustainability consultants thinkstep, which the New Zealand Green Building Council (NZGBC) says highlights a "hugely significant" area for action on climate change.
Buildings produce carbon pollution when using energy for things such as heating and lighting, and also during their construction, when pollution is emitted through the extraction of raw materials and the manufacture of building products.
Previous estimates, including last month's report by the Productivity Commission, suggested that our buildings were responsible for roughly 5 per cent of emissions – and maybe even as low as 2 per cent.
But the new report showed that buildings could amount to 20 per cent of New Zealand's carbon footprint when considering their lifetime "embodied" emissions, and the products and services that New Zealanders consume – rather than those that are destined for offshore markets.
The thinkstep report arrived at the larger figure for the climate emissions of buildings than previous studies because it uses a different methodology, which was widely applied internationally and has been used by organisations such as the European Commission, Danish Government, the National Bureau of Economic Research in the USA, and Motu Economic and Public Policy Research in New Zealand.
This approach differed because it allocated emissions to a sector at the point of consumption, rather than production, and because it considers the entire life cycle of buildings, including the extraction of raw materials, material production, the electricity and energy use of the building, and the treatment of construction waste.
"Buildings and infrastructure are some of the longest-lived parts of our society," said Jeff Vickers, thinkstep's Australasia technical director and lead author of the report.
"So it is crucial we act now to reduce their contribution to climate change pollution – both through reducing emissions from energy used during the building's life and through reducing the emissions embodied in the building products that we choose.
"Embodied emissions are increasingly being provided by building product manufacturers through Environmental Product Declarations."
The NZGBC now wanted to see the Government increase resources and efforts to reduce emissions from our buildings.
"The Government is taking some very welcome steps to cut our levels of climate change pollution," NZGBC director Sam Archer said.
"But they really do need to do more to tackle the emissions of our buildings, which make up a significant portion of our overall pollution.
"If they do, they'll ensure that our families will live in a cleaner, less polluted Aotearoa, and will also ensure that we'll achieve our important international obligations to tackle climate change."
Auckland now had more than 170 buildings which had received Green Star certification, with almost half those rated sites clustered around the CBD, and making up about 10 per cent of downtown buildings.
But homes in the city were frequently damp, cold and poorly insulated, which made them expensive to heat.
One city proposal that would have required all new city residential and commercial buildings to be green-certified and sustainable was opposed by some government departments and eventually scrapped during Auckland Unitary Plan hearings.