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How to Go from Six Stars to Seven Without Budget Blowout

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A recent Australian Building Codes Board consultation on proposed changes to the energy efficiency provisions for residential dwellings in the National Construction Code has foreshadowed a possible increase in performance requirements from 6 Star NatHERS to 7 Star.

If it goes ahead, the change would form part of the next iteration of the National Construction Code in 2022.

Before that happens, regulatory impact statements will be released as well as a draft of the Code for consultation and industry feedback in late 2020 or early 2021.

The impetus for lifting performance requirements comes from an agreement by the COAG Energy Ministers earlier this year to adopt a Trajectory for Low Energy Buildings. The Building Ministers Forum in July also endorsed the trajectory.

It might sound like a quantum leap. However, according to experts on residential design and construction, it is neither hard nor expensive to deliver a home that meets 7 Star NatHERS requirements.

The options presented in the ABCB scoping study emphasised the importance of the building envelope in terms of dwelling performance. It also suggested a whole-of-house approach facilitated through the use of Verification Methods. By applying these methods, you are able to take into account the interaction between various parts of the building, such as the building envelope, building services and on-site renewable energy.

The key factors the ABCB identify as key to minimising energy use for mechanical heating or cooling are the building orientation and internal layout; insulation and thermal mass; window type and size; passive solar heating for winter and shading for summer; the degree of building sealing; and the use of natural ventilation.

Executive Director of Anderson Energy Efficiency, Clyde Anderson, tells Jobsite one of the major differences between 6 Star NatHERS and 7 Star is that 7 Star is “less forgiving”.

It is possible to tweak elements of a build to achieve 6 Star, he said. With 7 Star, on the other hand, it is much more cost-effective to get all the elements in place at the early design stages.

The good news is those fundamentals, while needed to be taken into account early in the process, do not generally add to the project budget. What’s more, Anderson said, there is also a major financial gain for occupants—the upgrade from 6 Star to 7 Star delivers a 20 per cent reduction in energy costs.

“For the average household, that can equate to a couple of thousand dollars a year,” he said. 

At 7 Stars, most homes or apartments would only be uncomfortable in terms of heat or cold for several weeks of the year. Meanwhile, a 6 Star home is likely to be uncomfortable for a few months of the year in many Australian climate zones.

The starting place for achieving 7 Stars is the orientation, he explained. Once a build commences, it’s not a detail that can be corrected easily.

The CRC for Low Carbon Living’s free Guide to Low Carbon Residential Buildings – New Build, explains that optimum orientation allows a home to gain the maximum benefit of free warmth from winter sun entering living areas while minimising heat gain in summer.

In order to achieve that, Anderson said, window location needs to be considered carefully. In case of western or eastern windows, the builder should consider adding retractable shading, such as awnings, or louvres. This requires builders to understand passive design, he said.

Since an energy rating certificate is required at both the design stage and at the Certificate of Occupancy stage, he recommends builders “pick the brains” of the energy assessor.

He also suggests doing an indicative rating at the early stages of the design process. Thus, builders and designers can “see how a project’s tracking” in terms of its NatHERS score. That will also highlight where things can be improved and fine-tuned.

The energy assessor will be able to help develop workable suggestions for improving a design. For example, they can suggest changing the location of a garage, adjusting the extent of glazing, altering the home layout or moving a deck.

According to Anderson, the energy auditing process can serve as a form of “rigorous checking and quality assurance” for both design and construction.

The uplift to 7 Star has been on the radar for some years, and the Australian government has already laid some useful groundwork to help upskill the industry. It has provided free downloadable designs for 7 Star homes appropriate for each of Australia’s major climate zones and supporting information resources at the Your Home website.

Among the strategies the Design for Place 7 Star Home project suggests different material choices. For instance, using reverse brick veneer for strategic internal walls can add thermal mass. Similarly, waffle-pods with a concrete slab can be used in cold climates for added insulation.

The project also suggests using “cool roof” approaches, such as a light-coloured roofing material instead of a dark one. It also promotes thinking carefully about finer details like the impact of downlights on insulation performance are also highlighted.

Building products manufacturer CSR has undertaken significant research into the costs associated with building to a 7 Star standard. Their testing and modelling showed there is no additional cost added to the project budget—and that even going one Star further to 8 Stars would add a mere $2,300 to build costs.

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