New NZ homes emitting 5x more carbon than <2 deg budget allows

15 January 2020 by Jason Quinn

This first study of its kind in New Zealand attempts to calculate how much carbon new homes can emit if we are to stay within the 2 degrees warming limit set by the Paris Agreement—and how much carbon our new builds are actually using.

The outcome? Our typical built-to-Code new builds spew out five times more carbon than their fair share. To me, that’s a terrible number, but the researchers say they are relieved; that’s much less worse than what they expected.

The numbers necessarily rely on a lot of assumptions and I’d make different ones, but my conclusions would likely be similar.

A new home built today is assumed to have a 90-year life span (which is generous given the Code only requires key components like windows to last for a minimum of 15 years or maybe only 5 years if they components are easy to replace). Over 90 years, the energy used by the occupants is greater than the embodied energy used in building the house. But given the Paris Agreement’s 2050 target, the researchers focused on the carbon budget for the next 30 years. In that timeframe, almost half of the emission are in the materials, according to BRANZ’s David Dowell.

Bottom line? We need to reduce the carbon intensity of new homes by 80%.

The report’s authors recommended:

  1. Reducing the concrete and steel content (which typically increases in multi-storey dwellings);
  2. Reducing the size of our homes (currently 168 m2 average for detached homes and increasing)
  3. Higher density living: apartments and terraced housing. Not only for the carbon intensity of constructions, but for the carbon savings in other areas, such as shorter commutes and fewer cars.
  4. Designing to reduce energy usage.

Those recommendations are straightforward. A step-change improvement in the Building Code and a combination of stick and carrot initiatives to reduce footprint, increase density and choose wood products over steel and concrete would do it. Once again, politics not science is the sticking point.

—15 Jan 2020

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