Energy upgrade to Passive House standard for historic public housing in New Zealand

• Energy performance of 1940–1960s state houses in New Zealand was investigated.
• Different retrofit packages up to EnerPHit standard were defined for a pilot project in Auckland.
• Upgrade packages were modelled and evaluated using Virtual Environment and PHPP.
• Improvements to EnerPHit standard result in over 85% reduction of annual heating demand.

A large part of the current New Zealand housing stock was built prior to the 1978 policy of mandatory insulation. Its average low energy efficiency has significantly contributed to the recent growth of health inequality, fuel poverty and building decay. Considering that these old houses will be a significant portion of the future stock, their retrofit is decisive to meet environmental imperatives and to tackle urgent health issues. The mid-century state housing, in particular, is a repository of ‘authenticity’ that needs to be respected, studied, protected and revitalised. It proves to be suitable for effective energy upgrade interventions, setting a new performance benchmark for New Zealand retrofitting practice. This paper presents problems, opportunities, strategies and predictable effects of retrofitting interventions on 1940–1960s state houses, discussing results of empirical research on a representative sample located in Auckland. Different retrofit packages, up to the Passive House standard, were identified for implementation in a pilot project. Indoor and outdoor environmental parameters of the selected house and two control houses were monitored over a one year period and used to define the ‘base case’ for thermal simulation. Several upgrade packages were then modelled to assess their impact on the house's thermal performance, comparing annual heating requirements of various insulation and ventilation options.