Building passive houses in subtropical climates? A lesson learnt from New Zealand

Abstract

New Zealand's construction industry proves to be extremely conservative, reluctant to accept new products and technologies already established overseas. However, the country now faces the global issues of natural resource depletion and increased energy consumption, exacerbating its endemic problems concerning living conditions. Despite numerous studies proving the deleterious effects of unhealthy and uncomfortable dwellings on human wellbeing, there is still lack of pragmatic guidance on methods and technologies for future-proof constructions, both comfortable and energetically self-sustained. Even the most recent update of the current New Zealand Building Code is still insufficient to ensure comfortable indoors, imposing R-values that are just a fraction of those required by the European regulation in similar climatic areas. In the meantime, Europe is considering the Passive House (PH) standard as the means to achieve the requirements of the new Energy Performance of Buildings Directive, which requires all new constructions to be highly energy efficient, enabling the very low amount of energy required to be significantly covered by renewable sources. The success of the PH standard led to the question of whether it was applicable to New Zealand’s ‘unique’ climatic, social and market conditions. Referring to the construction process of the first certified PH built in New Zealand (and in Australasia), this paper reveals the challenge of introducing the standard to what is perceived as a sub-tropical country. After having debunked the local ‘myth’ of the climate, it traces the brief but rapid evolution of the PH in the country, from the first prototypes, to the first certified detached house recently completed in Auckland, finally to the ultimate projects - already in their completion phase – of ‘zero energy’ PHs, which are equipped with on-site renewable energy generation systems. In order to verify if the PH standard is a viable solution for New Zealand, results of PHPP calculations produced for the NZ’s first certified PH and two ‘zero energy’ PHs currently under construction in the North Island are analysed and compared to the PHPP calculation of a Code compliant house. The economic feasibility of this model is also assessed by running a simplified cost analysis and comparing the results to standard NZ construction costs for the same building category. Results show that the PH standard represents a suitable solution even for a sub-tropical country such as New Zealand: despite market constraints, PHs prove to be economically viable, especially considering long term benefits due to energy and health costs savings. At the national scale, the success of the most recent ‘active’ solutions could contribute to revitalize the image of New Zealand as a green country, which has greatly invested in clean energy but not on energy conservation strategies, first of all in the building sector, one of its biggest energy sinks.