Recent changes to the Commercial Building Disclosure (CBD) Program mean that as of 1 July 2017 1000 square metres will become the mandatory disclosure threshold on commercial office buildings. The threshold is currently 2000 square metres.
The CBD Program requires that energy efficiency information is provided when a commercial office space is listed for sale or lease. The CBD program ensures that any prospective buyers or tenants are kept informed and that the energy efficiency of large office buildings is improved.
More information here.