Chapter 2 Passivhaus

The passivhaus approach originated in Germany. The approach is also increasingly used elsewhere in Europe and North America. While originating in cold climates the method applies equally to warm climates - the physics of heat transfer are, after all, universal. For example, the Austrian embassy in Jakarta uses passivhaus principles and there are an increasing number of residential dwellings in Spain built to Passivhaus standards. There are now a number of buildings in Australia certified to the passivhaus standard and many more under construction - the Australian Passive House Association is the professional body that promotes passive house principles in Australia.

2.1 The advantages of Passivhaus

There are numerous sustainable building philosophies, most of which seem to have a strong “feelgood” basis and much more limited technical rigour to support them. We liked the passivhaus approach because of its scientific basis:

  • its’ starting point is the evidence on air temperatures, temperature stratification, air movement (drafts) and radiant surface temperatures which are known, based on empirical studies with human subjects, to produce conditions which are perceived as comfortable,
  • it then adds in the accepted volume of fresh air required for good indoor air quality (30 m2/person/hr),
  • it applies the physics of heat transfer and hygrothermal analysis (i.e. moisture transfer) to ensure the desired performance is achieved,
  • it seeks to achieve comfortable internal temperatures using no more heat load than can be carried into the building in fresh air required to keep the occupants comfortable (that is, exceptionally low heating and cooling requirements), and
  • extensive verification is required to ensure what is desired and designed is actually built.

While passivhaus is fairly common in Germany, and related standards such as Minergie-P are common in Switzerland, it’s fairly new to Australia. Indeed, when we started there were fewer than six certified passive houses in Australia and only one certified to the retrofit standard.

Our home is NOT passivhaus certified. We feel just short of the airtightness criteria to meet the certification.

2.2 How is passivhaus different?

Australian building practice increasingly recognises the importance of bulk insulation as a means of maintaining internal building temperatures, and there is some understanding of the importance of glazing. There is also some recognition of the role thermal mass (e.g. concrete slabs and reverse brick veneer) can play in storing and releasing heat within a home. However, there is almost no recognition of:

  • the importance of airtightness,
  • thermal bridging, or
  • verification of modelled performance.

The passivhaus approach is different insofar as it requires extreme levels of airtightness, a continuous insulation layer and verification that what has been designed has indeed been built. More information on the approach is available here and from the Australian Passive House Association.

We would emphasise the importance of verification - there is strong evidence to suggest that the vast majority of new homes built in Australia that are supposedly 6-star energy rated are performing closer to 3-stars. This is a massive performance gap; a 6-star home in the Moorabbin climate zone would require 35 kWh/m2}/year of heating and cooling but a 3-star home requires more than twice this level of energy (84 kWh/m2/year). This has huge repurcussions for the ongoing operating costs and comfort for occupants. The Passivhaus approach imposes a much higher level of rigour to provide some reassurance to the owner that they’re getting what they’re paying for. Given the cost of building a house we felt this additional insurance was well worth the effort.