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People often refer to Building Code of Australia (BCA) requirements being ‘6 stars’. However, the 6 stars requirement is actually one of a number of available pathways for compliance with the BCA energy efficiency requirements.
The BCA is a performance-based code, meaning that it allows for a number of available pathways to comply with the mandatory Performance Requirements.
For energy efficiency, the relevant Performance Requirements that must be complied with are P2.6.1 and P2.6.2.
Performance Requirement P2.6.1 sets the benchmark that a home needs to achieve in terms of the level of thermal performance of the building envelope (i.e. the building fabric).
The objective of this Performance Requirement is to enable a building to facilitate the efficient use of energy for artificial heating and cooling, taking into account its location and surrounds.
This means the floor, wall, roof, windows, etc. of the building shall be constructed so the house maintains a certain level of thermal comfort naturally. Artificial heating and cooling can still be installed but the building design and materials used must maintains a certain level of thermal comfort naturally, thus reducing the amount of artificially heating and cooling needed. Ultimately, the BCA’s requirements aim to reduce greenhouse gas emissions via the efficient use of buildings’ services.
Performance Requirement P2.6.2 applies to the fixed services installed in the building and relates to their efficiency and power usage/supply.
The requirements consider the geological or geographic conditions found at the building site. Across the various climatic conditions found in Australia, some areas will be heating dominated and others will be cooling dominated.
To meet the mandatory Performance Requirement P2.6.1, the BCA provides three different pathways, as well as the option to use a Performance Solution.
Using any of the pathways should result in a home having similar energy demands for maintaining an ambient temperature.
These pathways include:
This is the best-known method and uses software programs (e.g. BERS Pro, Accurate and First Rate 5) to assess the heating and cooling demands of a building to maintain an ambient internal temperature.
These demands are compared to performance bands that indicate the ‘star rating’ of that building.
The software outputs a certificate with a star rating and, for most homes, if you achieve 6 stars or greater, you achieve compliance.
This method adds up the thermal resistance (R-value) of each building element to quantify the building’s performance and compares it against prescribed minimums.
This involves following the diagrammatic arrangements written into the BCA in Parts 3.12 when constructing the building.
The diagrammatic arrangements might, for example, say the external wall needs to meet a minimum R-value of 2.8 in climate zone 6. For this particular building, walls are to be brick veneer. The BCA provisions specify that the brick veneer wall (i.e. bricks, cavity and framing) achieves a total R-value of 0.56. This means that insulation or sarking and insulation will need to be installed to make up the shortfall (i.e. R2.5 insulation or R2.0 and sarking with a minimum R0.5).
Essentially, this method is like the recipe or checklist approach that you work through, complying with the individual provisions written into the BCA to achieve compliance.
This method compares the performance of the modelled proposed building against a similar building modelled using the DTS Provisions (often called the ‘reference building’).
If the proposed building outperforms the reference building, compliance is achieved. This method is completed as a Performance Solution to meet the BCA.
The BCA also always allows a pathway for the development of another type of Performance Solution. This can be a unique solution that demonstrates the home meets the Performance Requirements of the BCA and is often demonstrated by expert judgement.
The various pathways have their benefits, so selecting the appropriate pathways should be done on a case-by-case basis. One of the key areas to consider is the consistency of the intended construction with traditional building methodologies or the need to have flexibility with the building elements.
To satisfy the building services Performance Requirement P2.6.2, this is commonly achieved by complying with Part 3.12.5, as appropriate, for the services installed in the building.
When using any of the pathways for energy compliance, there are additional considerations relating to installation of insulation, thermal breaks, building sealing and air movement that require consideration when detailing the external envelope of the building.
These requirements are prescribed in Parts 3.12.1, 3.12.3 and 3.12.4.
In NSW, Part 3.12 does not apply and is replaced with the requirements for NSW in Appendix A.
This requires that a BASIX (Building Sustainability Index) assessment be completed.
In NT, Part 3.12 is replaced with the requirements of BCA 2009 Part 3.12. For other states, local variations included in the Part 3.12 should be considered.
There are also some other variations or additional provisions that apply in some states. As such, it is important to check with your local authority or administration for any specific state or territory provisions that may override the BCA provisions.
Note: The above information is general advice only and HIA recommends that prior to using any method for demonstrating compliance with the BCA energy efficiency requirements, builders, designers, etc. discuss it with the relevant energy assessors, building certifiers and regulators for the subject project to ensure the BCA requirements are being satisfied.
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