MBIE’s options versus FMI ZE – costs Before comparing MBIE and FMI’s cost estimates, we need to acknowledge two caveats. House design: Between MBIE’s and FMI’s builds we are comparing apples and oranges to some degree. MBIE’s house has four bedrooms and a 150m2 floor area, whereas FMI’s home has 3 bedrooms on a 120m2 floor area. MBIE has also restricted its design changes to the energy efficiency of the building envelope while FMI, as described elsewhere, has also addressed water heating and increased airtightness which has added cost. Recency of costings: MBIE will likely have compiled its building costs in early 2021 whereas the FMI cost data in Figure M was refreshed late in Q3 2021. Again, we are to some extent comparing apples and oranges. This is partly due to the ongoing rises in building material costs throughout this year and partly to the potential for price relativities of key materials to have shifted. Shifting relativities could affect the premium payable to deliver an energy efficient home. Confirming the build cost premium for FMI’s ZER design is a core reason for the next step of building a test house. With those caveats noted, we can return to comparing the cost premiums for the MBIE options and for FMI’s ZER house. The premiums estimated by MBIE in their April consultation document struck us as high for merely improving the insulation in the building envelope, even acknowledging they are for a larger house. The highest premium is $50,000 or about 12% of total home building cost excluding land for Option 3 in Climate Zone 6. This concerns us: if these
numbers are not verified with relevant sources in the industry, the high premiums could sap interest and support for energy-efficient improvements. By contrast, our FMI ZER house in Climate Zone 6 – the house that needed only a fifth of the energy for heating demand as MBIE’s Option 3 – carries a premium over a Code-built house of slightly over 4%. Figure M shows that about 35% of the GST inclusive premium is driven by very highperforming R0.95 windows, with the remaining two thirds split fairly equally between the investment in air tightness (ventilation, spray foam and weatherisation layer) and the appliances. Note that the recent costing we obtained in fact priced a heat pump into the Code built home. Rather than make estimates to align the Code house’s air heating method back to our thermal modelling assumptions, we have left it as is to reflect an emerging trend in group home builders’ choices. Importantly, the cost impact of about $1000-1500 on the ZE premium is truly lost in the rounding! For the solar panels, we were advised by a specialist company to use a one-size solution across all climate zones. This aligned well with our views on simplicity. We have costed an installation of 18 panels each rated at 370W capacity to provide a system capable of delivering the annual energy demand of the ZE house in all six proposed climate zones. The premium for the ZE home is a little over half as much again as for the ZER house. Costs are of course shifting all the time as technology changes and as global and local supply-demand balances alter. What is right at the time of writing will soon be out of date.
