Existing homes

Papakōwhai Renovations

This 10 home case study project trialled different combinations of retrofit interventions aimed at making homes warmer, drier, and more energy efficient. Results were monitored before and after the renovations to see which retrofit combinations were the most effective.

The project asked:

How can we make any house, whether built ten, twenty or fifty years ago, more energy efficient, more water efficient, healthier to live in and more affordable for its occupants?

It showed clearly that insulation needed to be accompanied by heating to get lower energy bills AND warmer houses.

The houses

House 1 received a a standard thermal retrofit with efficient heating and a heat transfer system. Temperatures improved by 1-2oC and electricity use fell with a reduction of 12% in hot water energy use during winter
House 3 was renovated with a high thermal retrofit with efficient heating and solar hot water. Temperatures increased by 1.7oC to 3.8oC and there was a reduction in electricity use of ~33% over winter.
House 5 received a standard thermal retrofit with efficient hot water and a heat transfer system. Temperatures improved by ~1oC, although these were still too cold for good health, and electricity use reduced by 35%.
House 7 received a moderate to high thermal retrofit with some heating, hot water and ventilation improvements. Temperatures increased by 1oC and relative humidity was over 70% for 75% of the time. Electricity use reduced by 20% over winter.
House 9 received a moderate thermal retrofit with cylinder and pipe wraps. Temperatures increased slightly by 0.4oC although less space heating was needed. Water heating efficiencies meant overall energy use reduced by 20%.

House 2 received a basic retrofit package matching insulation standards of the day, plus interventions to reduce and extract moisture. Temperatures improved by 1.1oC to 1.6oC and hot water efficiency reduced energy bills by 11% during winter.
House 4 was sold and left the project.
House 6 received a basic ceiling top-up, the equivalent of earlier government subsidies, and wrapping of hot water cylinder and pipes. There were no improvements to temperatures or humidity but an 11% reduction in hot water costs.
House 8 received a moderate to high thermal retrofit with a solar hot water system. Temperatures stayed the same but the house required less energy to heat. 70% less electricity was used to heat water during winter. Overall, energy use dropped by 15%, thanks to space heating savings.
House 10 received a high thermal retrofit with efficient heating and a solar hot water system. Temperatures increased by 4oC , hot water energy use reduced by 70%, and overall household energy use reduced by 30%.
Papakōwhai Renovations case studyDownload
What else is in the knowledge base?
  • Papakōwhai Renovations: Project summary and case studies
  • Papakōwhai Renovations: Householder perceptions and experiences
  • Papakōwhai Renovations: Impacts on householders and dwelling performance
  • Cost benefits of sustainable housing retrofits
  • Clawback of heating services in Beacon research homes
  • Solar water heating in NOW Homes and Papakōwhai Renovations
  • Sustainability options for retrofitting New Zealand houses: Theoretical cost benefit analysis
  • Sustainability options for retrofitting New Zealand houses: Energy