What does it take to build a Certified Passive House in New Zealand?

Passive House in Whanganui

1) An optimal level of thermal insulation of opaque building elements, like walls, roofs and floors.

This optimum is found based on factors like the local climate, geometry, orientation and occupancy of the building. Thresholds for both heating and overheating apply. For a Certified Passive House in Auckland, you may get away with as little as 90mm insulation in the walls, if other factors are favourable.

2) Optimally sized and insulated window frames with high quality, optimised glazing.

The optimum is found based on factors like the local climate, geometry, orientation, shading, comfort and daylighting. Thresholds for both heating and overheating apply. For coastal regions, very efficient double glazing in a timber or effectively thermally broken uPVC or aluminium frame may suffice to tick all the boxes, if other factors are favourable. External, moveable shading is essential to prevent overheating.

3) Thermal bridge free design and construction.

Careful detailing is required to eliminate byways for heat to escape, which results not only in unnecessary heat loss, but also in low interior surface temperatures, offering potential for indoor humidity to condensate.

4) An airtight building envelope.

An airtight building envelope is required to prevent moisture build-up in cavities, and to keep outdoor elements, like draughts, noise, contaminants and unwanted fauna outdoors. It is also essential to safeguard the performance of the insulation, and any purposeful ventilation system.

5) Heat recovery from ventilation.

A constant supply of fresh air is essential for the well-being of people and pets inside a building. However, by constantly exchanging warm air for cold outside air, heat is unnecessarily lost. Unless the bulk of the heat is recovered from outgoing air. While it is not a requirement for Certified Passive Houses to have a heat recovery ventilation system (unlike openable windows, which are a requirement), it is a smart decision to use very efficient and independently tested heat recovery ventilation, to curb ventilation heat loss without sacrificing the constant supply of fresh air.

6) Quality control.

Without a robust means to test a design or building, setting goals is only an exercise in wishful thinking. Certified Passive Houses are tested at the design stage, but also in the real world. Arguably, both tests are equally important, but errors in the design stage are more easily fixed. It is therefore greatly beneficial to use a tool that enables an accurate prediction of the performance in the real world. For Certified Passive Houses, the Passive House Planning Package (PHPP) has to be used, which was widely tested to be a reliable design tool. Using PHPP, designers are able to find optimum levels of insulation, the most beneficial window configurations, as well as the best ventilation strategy. It's not a race to zero consumption. It's about getting the best outcomes your budget can buy.