There is so much information around about the National House Energy Rating System (NatHERS) that I’m not going to cover anything much here. The minimum standard is for a 6 star (out of 10) rating, with lots of folk advertising and promoting much higher ratings.
I have a somewhat contrarian view on this – you can spend a great deal of money achieving a high energy rating for your house in an effort to reduce your energy usage, but I would argue that installing a solar& battery system to cover the increased energy requirement is more more environmentally friendly, cost effective and yields a more liveable house.
A high star rating house, >8 star, can often compromise your living – house orientation (inconvenient with land orientation, loss of view), size, aesthetics with internal and external building material restrictions, window size and orientation, house ventilation (can be really stuffy/smelly when you’re shut up tight) etc etc. One example is ventilation – in summer, open a window. Great idea. In winter, your heat literally flies out the window, so to have a good comfortable environment inside, you need to have a heat recovery system to bring warm fresh air into your house, adding cost and complexity.
Achieving a high star rating is expensive, difficult to achieve, restrictive, and has high embodied energy. If you are trying to be environmentally friendly by going for a high energy rating, then make sure you look at the embodied energy of the build.
CSIRO research found that the “average” house has 10 to 20 years worth of energy use embedded in it.
If you’re looking for high thermal mass, specific materials, added build complexity and additional equipment you will likely be adding significantly to your embodied energy.
We made a different choice – orient the house for the view, with outdoor living sheltered from the prevailing winds. We have skylights and clerestory windows to bring light into the living room from overhead, east and west. We’ve selected double glazed windows with low e glass (light bridge). This gave us a 7.5 star rating at low cost, without compromise on how we wanted to live. It adds very little additional embodied energy to the house. We selected a look for the house that we liked – recycled red bricks with some black steel sheeting. We were comfortable with the dark colours because we were more concerned about winter heat, than summer cooling. Blog post Cooling.
Use of the recycled bricks reduces the embodied energy. I must admit that our house size and small amount of steel sheeting are not good from an embodied energy view point.
From an environmental perspective, our heating is sustainable – purpose grown fire wood trees (blue gums) that coppice well so will continue to regenerate and regrow even after they are cut down. Our cooling is sustainable – we will produce double the electricity in summer than in winter, so we have excess power available in summer to run air conditioning and/or fans, as required, to cool the house.
Even upsizing the solar to cope with additional cooling load is likely to be cheaper than a significant increase in your house star rating.
Solar with batteries is likely to be the far cheaper, easier and environmentally friendly option to get a low energy use house – on or off the grid.
Disclaimer I haven’t done a comparison between embodied energy of the solar system and a high star rated house, but solar panels do produce more power than they take to make.