14 Dec Can Perth Home Builders Rely on the Stars?
When we talk about a sustainable home in Australia, people often talk about star ratings. Today we look at whether the stars really give a good indication of the environmental performance of a house – particularly in a Perth context.
NatHERS or the Nationwide House Energy Rating Scheme rates the thermal comfort of a home on a scale from 0-10. A 0 star home will give barely any protection from the elements, while a 10 star home should not need any heating or cooling to remain comfortable all year round. The higher the rating, the less likely you will need to heat or cool your home.
The reality is somewhat different, particularly in Australia’s hotter climate zones (such as Perth). A CSIRO review of the new 5 star standard for homes compared to the previous 3.5-4 star standard had the following findings in a review of over 100 built and rated homes:
- Energy required to heat homes in winter was reduced (as one might expect)
- Energy required to cool homes in summer was increased
Although cool climates such as Melbourne had significant reductions in energy consumption with the higher star ratings, in hotter climates such as Brisbane the net annual energy consumption was higher in homes with the higher star rating. Perth was not included in the study; however with very hot summers and mild winters it is highly likely that the results would be similar to the Brisbane homes.
Award winning architects Welke and Harris noted that many of their Northern Territory homes which have not needed any cooling over the past few decades achieve very low scores, some even 0 stars. They attribute this to the rating’s focus on sealed houses with high levels of insulation as opposed to a holistic approach using passive design strategies to exploit the local climate.
Further, while thermal comfort is a very important element for a low energy home, this is not the only factor to consider in the quest for a sustainable home. For example, in Perth where we are very remote, we should be taking into account where the materials for our homes are sourced. In such a dry climate, we should have a strong focus on water consumption.
If you are looking to build a sustainable home, you should consider what sustainability means to you and set your goals accordingly. It may be enough for you to simply ensure sustainability is considered in the design process. Maybe you want a home that uses very little water, or is built only using renewable materials. Or you might want to go down the path of rating your home.
NatHERS is by no means the only way to rate your home’s sustainability. One of the more comprehensive rating tools is LEED for homes. This rating system gives a substantial allocation of points to homes with high thermal performance (but uses a far more robust mechanism for estimating this than NatHERS). It also takes into account factors such as embodied energy, indoor air quality, materials, construction methods, location, landscape design, water efficiency and impacts on the urban heat island effect.
Two local sustainability gurus in Perth have started their own rating system called etool which looks at both the embodied energy and operational energy of a house in parallel giving a holistic picture of the lifetime impacts of a home.
Whatever your goals may be, my advice to those building their own eco-home is to look beyond the stars, as these may not give you the home you are looking for!