Passivhaus and NatHERS – Our View

How do we deliver Passivhaus projects?

NatHERS is the national energy rating tool for homes that is required under the National Construction Code and planning process for every new home, with a minimum 7 Star rating needed under NCC 2022.
The Passivhaus method of energy modelling takes a more detailed approach to each building component and provides a better indication of the building’s final performance. The model used (called PHPP) has been refined through empirical verification of actual building performance.

Learn more about the oldest Passivhaus in Darmstadt which has been monitored for 25 years.

In our projects, we have found that our Passivhaus projects generally correlate to a NatHERS star rating of around 8.0. A high NatHERS rating requires good insulation specifications, however it should be noted that:

The comfort range in NatHERS is wide and may not suit occupants in practice. Passivhaus aims for a consistent 20-24°C year-round.
A high NatHERS rating may still result in a leaky building. Losses in conditioned air means high energy use and high bills.
The software used for NatHERS doesn’t permit thermal bridge modelling or detailed component inputs to the same extent as PHPP.
NatHERS ratings are often prepared early in the design process, and there is no requirement to check that the specifications are delivered during the build.
NatHERS assesses projects based on annual consumption. A black roof and no eaves in Melbourne may improve the winter performance, but adversely affect summer performance – and this would not be reflected in the star rating.

There are more intricate differences between the systems, and we acknowledge that NatHERS has to be applicable for projects across the country.

In practice, we prefer the Passivhaus model for its exacting quality assurance process. It is rigorous, comprehensive, and has a process to verify construction quality, final airtightness, and system commissioning. It is a lot more work for us, but it is time and money well spent and is reflected in the final product.

We use PHPP as a primary assessment, with NatHERS as a secondary check when designing our projects.