Calculations are done for the fenestration.

If the first concept design does not comply, the following may be implemented to bring the design to compliance:

• reduce glazing ratio
• specify double glazing and performance glass
• implement horizontal shading devices

A 3D energy model is built, with details of actual location, fabric, operation and systems embedded.

Insulation levels must be met for the roof, prescribed by the climate zone.

An hourly simulation is run for the building using certified thermal calculation software.

Rational glazing and insulation properties are chosen to balance cost and performance. There is no minimum glazing or insulation requirement.

Shading provided by surrounding buildings may not be accounted for, and space use and the efficiency of energy systems may not be considered to show compliance.

Annual energy and peak power use are quantified, accounting for all the building's energy uses.

These are reported in detail, and a building energy performance summary is generated.

Once the prescriptive boxes have been ticked, forms may be signed and submitted to council alongside building plans.

If the building's annual energy use and peak power are less than the allowances in the XA regulation, the building passes the rational assessment.

If the energy use is shown to exceed the allowance, the most cost effective energy conservation measures may be advised to achieve the required performance.