Online news source, the Fifth Estate reports that the Australian Passive House Association has developed a new online resource showing the difference between designing for 7 Star NatHERS and designing for different degrees of Passive House.
As Willow Aliento, from Fifth Estate, points out, "For the average homebuyer, it’s difficult to know whether a home with a 7 Star NatHERS rating is actually performing like one."
The user interface encompasses both the building fabric itself, and the quality of the building fabric with options ranging from minimum – 7 Star compliance – to excellent. It also shows how steps towards the Passive House standard will influence both thermal comfort and annual energy bills.
Builders promote 6 Star NatHERS homes as a bonus for buyers, rather than recognising the fact that this is the minimum requirement of our building codes. This leaves much of the industry aiming for 6 Stars and believing they are buying an energy efficient home - when it is in fact the poorest thermal quality of home you are legally allowed to build.
With our current building certification systems, the reality is that most houses are unlikely to be built to the rating requirements anyway. While our Star rating system is based on the use of some smart software programs, in reality they are mainly a paper based exercise. This was highlighted in the National Energy Efficient Building Program study undertaken by the federal government in 2016, which tested over 700 houses built to the 6 Star standard or above and found most were insulated to a 3-3.5 Star standard as actually built.
Air sealing and leakage is a major factor in why houses as built are performing so poorly. Habitech houses approach Passivhaus standards, and one house, which utilises heat recovery technology, has an air-change rate of 1.15 air changes an hour at 50 kilopascals. The Passivhaus standard is 0.6, while a typical new home might be 20-30 . Have a look at the graph below to better understand this.