designing for sustainability

All new buildings are subject to rules regulating thermal performance of a building in section J of the building code of Australia.
Section J is only a minimum requirement, other certification systems such as GreenStar, NABERS or BREEAM provide (sometimes real estate agents put these on the 'for sale' or 'for lease' signs).

Having these certifications usually makes the building more attractive to buyers/occupants. They are particularly attractive to government organisations since government buildings are required to meet certain requirements for enegy ratings.

passive design

Buildings don't use energy, services do.

Passive design recognises that a building's environment and materials can be used to increase energy efficiency. it means a building's design has to take into consideration things like:
you may notice your house is set up to take advantage of its relationship to the direction of the sun! many houses are designed so bedrooms face south to keep you cool at night in summer.
even if we've designed a building using the most thermally efficient materials, it's likely we'll still need to use energy to run it

luckily, sustainable buildings can be used to harvest renewable energy, such as wind and the sun. the less reliant on fossil-fuel generated energy, the better!