For new builds / renovations
Before you sign any contract or make any drawings, research home efficiency or engage a professional.
When you have the chance to build a house from scratch, spend a little more and you'll have a yearly electricity bill under $500, no gas bills and a super comfortable house all year round. The additional cost over a standard build for the upgrades is modest at around 10% of the total build cost. If done after the build, this is likely to increase to 30%.
The Your Home website has detailed info on all of the major considerations for efficiency and comfort if you'd like to do the research part yourself. Then there's the issue of compliance.
Compliance - the elusive 6 star house
Having the specifications is only part of the work - a 6 star house rarely ends up achieving that rating in practice. Short cuts can easily be hidden on many of the recommendations so compliance is an issue. All the little details add time and costs to a project and unless they are inspected and followed through with, the results can come short of expectations. Once a house is completed, energy upgrades become markedly more expensive.
The key stages for inspection are before the cladding and plaster go up.
Inspect details like wall insulation before the plaster goes up. It's too costly to fix afterwards.