In 2003, thermal performance requirements for residential buildings were added to the Building Code of Australia for the first time. The initial performance requirement was 4 Stars in the National House Energy Rating Scheme (NatHERS) as simulated using the benchmark software AccuRate. In 2006, the requirement rose to 5 Stars, then to 10 Stars in 2010. This all sounds great. The increasing rating requirements of NatHERS provides a measurable and predictable target for improving the energy efficiency of Australian homes. But the building products industry wanted to know, how accurate is AccuRate?