While Green Star, the National Australian Built Environment Rating System (NABERS) and Nationwide House Energy Rating Scheme (NatHERS) have different origins, and were designed with different uses in mind, there is an increasing convergence in their application.

Green Star

The Green Building Council of Australia (GBCA) developed the Green Star office rating tool in 2002. Today, there is a wide range of tools available for different types of buildings, such as educational facilities and multi-residential developments. Energy efficiency is a strong focus of the tools but it also addresses management, innovation, indoor environment quality, water, materials, emissions, transport, land use and ecology.

A Green Star assessment is comprehensive, and is designed to recognise national and international best practice and leadership. To achieve a star rating usually requires a significant investment in design and capital cost.

All Green Star tools are voluntary assessments and can be obtained as a design or as-built rating. Given that a formal certification requires at least four stars, an official rating places a building amongst the top 25 per cent of the market in terms of environmental impact.

NatHERS

At the other end of the spectrum to Green Star, the NatHERS tool is used to assess house designs against minimum compliance standards set by the Building Code of Australia (BCA). This framework is used by the more familiar names of First Rate, BERS or ACCURATE.

A NatHERS assessment measures the thermal performance of the envelope of the building, taking into consideration some aspects of location, orientation, shading and overshadowing as well as building fabric and glazing. The result is a relative estimate of heating and cooling demand.

The 2009 version of the BCA requires an individual dwelling to achieve a rating of 5 stars in Victoria. In 2010, this threshold was raised to 6 stars or equivalent.

National Australian Built Environment Rating System (NABERS)

While Green Star and NatHERS predict building performance, the NABERS tool assesses real performance. Energy is assessed by reviewing actual energy bills, indoor environment quality with on site measurements, water consumption from bills and waste generation by quantifying outputs.

With the introduction of the Commercial Buildings Disclosure schemeimplemented on the 1 November 2010, offices with a floor area greater than 2,000 square metres will be required to disclose their energy performance with a NABERS rating when the space is being leased or sold.

As part of the NABERS energy scheme, design assessment protocols have been developed. These protocols predict the future rating of developments through thermal computer simulation and are aiming to assist design teams in providing a building that, later on, will achieve the desired performance. While a successful computer simulation cannot guarantee that the building will achieve its target in the future, and no formal certification can be obtained just through simulation, the protocols are an important part of designers’ toolkits that help evaluate different scenarios.

The protocols also form the basis for the energy assessment within the Green Star tools. Even though Green Star and NABERS have different base case benchmarks, the protocols are used in Green Star to determine the energy performance and the resulting points achieved.

The outlook

As environmental awareness in the community grows, environmental performance assessment tools are being used to set quantifiable targets for building design and operation. Rather than prescribing fairly inflexible and thus untargeted deemed-to-satisfy provisions, the tools allow designers to innovate, create their own solutions and evaluate them using the methodologies and benchmarks of third party tools.

With energy efficiency being one of the most salient aspects of modern building design, the scheme will move NABERS Energy ratings increasingly into the industry spotlight. Comprehensive Green Building tools such as Green Star will ensure that the required optimisation of the way we use energy within our buildings is balanced with other important design aspects of the built environment.