What Is BASIX?

BASIX is the Building Sustainability Index used for residential development in New South Wales. It forms part of the NSW planning and approval system and establishes project-specific requirements for water use, energy use and thermal performance.

A BASIX assessment uses information about the proposed dwelling, including its location, size, glazing, construction, insulation, water measures and building services. The assessment also records construction materials so the embodied emissions associated with the development can be calculated and reported.

Once the applicable BASIX requirements have been satisfied, a BASIX Certificate can be generated. The Certificate lists the sustainability commitments that must correspond with the approval plans and be carried through into the completed development.

The BASIX Materials Index calculates and reports the embodied emissions associated with construction materials entered for an applicable residential development in New South Wales.

Unlike the BASIX Water and Energy sections, the Materials Index does not currently apply a separate score or emissions limit that the project must achieve. Its present role is to quantify material-related emissions and record them within the BASIX assessment.

The result depends on the proposed building geometry, construction areas and selected material systems. Accurate information is therefore important even though the Materials Index is currently a reporting requirement rather than a standalone performance target.

Passive design uses the building’s orientation, form, windows, shading, insulation, ventilation and construction to respond to the local climate before mechanical heating and cooling systems are considered.

Within BASIX and NatHERS, these decisions influence the modelled heating and cooling demand of a residential design. A well-coordinated passive response can improve thermal performance, reduce pressure on later specifications and make the final commitments easier to deliver.

Passive design is not a checklist of universally beneficial features. Each measure affects the others, and the appropriate balance depends on the climate, site, dwelling form and way the home is expected to operate.

Windows are one of the most influential parts of a residential thermal-performance assessment. They provide daylight, views and ventilation, but they can also transfer heat more readily than insulated walls, roofs and floors.

Within BASIX and NatHERS, window performance is determined by more than whether the glass is single or double glazed. The complete window system—including the frame, glass, opening type, size, orientation and shading—affects the modelled heating and cooling demand of the dwelling.

The final assessment may establish maximum U-values, acceptable Solar Heat Gain Coefficient ranges and dwelling-specific window requirements. Those values must then be coordinated with the architectural plans, window schedule, supplier information and installed products.

Thermal performance is the part of BASIX that assesses how much artificial heating and cooling a proposed dwelling is expected to require. It considers how the building envelope responds to the local climate before the efficiency of the installed heating or cooling equipment is taken into account.

The result is influenced by the dwelling geometry, orientation, glazing, shading, insulation, construction systems and exposure to external conditions. BASIX compares the estimated or simulated heating and cooling loads with the maximum loads allowed for the project.

A project must satisfy the applicable heating and cooling requirements using an accepted assessment method. Depending on the dwelling and project pathway, this may be the BASIX DIY Method, NatHERS Simulation Method or Passive House Standard method.