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By Willow Aliento
October 15, 2018
The Victorian Government recently announced a grant of $2.18 million as part of a pilot Net Zero Homes project that will see Stockland, Metricon Homes and SJD Homes deliver showcase energy-efficient homes in key Melbourne growth areas.
It’s part of a wider green building trend—so Jobsite asked experts in sustainable design and construction what sets a net-zero home apart, and how both builders and home buyers can find value in the approach.
Dr Rob Brimblecombe, Manager, Energy and Sustainability at Monash University, led the team for Australia’s first Passive House commercial office project. He co-authored Positive Energy Homes, published by CSIRO in 2017, with Kara Rosemeier.
According to Brimblecombe, a simple definition of a net-zero home is one that can generate as much energy as it uses annually. In the urban setting, it is generally also necessary for a home to be all-electric, rather than having gas as well. Such practices obviously result in dramatically lower bills for the home’s occupants.
Design is key, he says, when the energy split between lighting, fixed appliances, hot water and heating and cooling is considered—heating and cooling are generally the “lion’s share” of energy use. However, good design can more or less eliminate heating and cooling, Brimblecombe says, when combined with a home being well-insulated, having good windows, and good solar control.
In winter, solar control is about gaining free heat from the sun. In summer, the key is being able to open a home up for ventilation as well as also to stop heat from getting in.
Not only is the right amount of insulation important, he says, but also the detail around it is crucial. If there are gaps in the insulation, it won’t work. An air-tight building envelope is, therefore, essential. Since heat looks to move from zones of high temperature to zones of lower temperature, gaps and cracks at ceiling height can compromise performance.
In the Passive House system, energy-efficient heat recovery ventilation systems are generally used to ensure high-quality indoor air enters the home. They provide extremely economical heat in winter, and in summer they can remove heat from the interior.
For other homes, operable windows and doors can provide the fresh air and in warm weather can also purge excess heat.
One benefit of good design is that adding thermal mass as part of the building’s thermal performance strategy should not be necessary, Brimblecombe explains. This means lightweight construction can perform just as well as masonry-type construction.
Another important part of the methodology for delivering net-zero homes is to “design for construction”, Brimblecombe says. “It means using a method that doesn’t require a lot of chasing, detailing, or taping.”
Brimblecombe says that in the net-zero home space, practitioners are not primarily talking about energy efficiency as the goal. Comfort and a quality indoor environment are what consumers experience, with energy efficiency as a happy “by-product.”
The Green Building Council of Australia, as a member of the World Green Building Council, is committed to working towards all buildings being net zero in operation by 2050. It is also specifically focusing on residential dwellings through its new Future Homes program.
Jorge Chapa, GBCA Head of Market Transformation, tells Jobsite the difference between a net zero home and one that achieves NCC compliance is a net-zero home is one that through the combination of better design, building practice or technology—or a mix of these things—is energy efficient and comfortable.
It is also a home that derives its energy from renewable energy, whether that is on-site solar such as rooftop PV or renewable energy sourced from offsite.
By comparison, a code-compliant home is built to a standard that is focused on ensuring it doesn’t “fall down, burn down or be excessively uncomfortable to live in,” Chapa explains. He says that the real value a builder can provide through net-zero approaches is delivering a good quality home by utilising good design and good careful building techniques at the same cost as a code-minimum home.
Market forces stimulating the trend toward net-zero include consumers recognising that they should have better housing in terms of quality and comfort.
Another enabling trend stems from the fact that technology required to achieve net zero has evolved. While Australian supply chains are still maturing, technologies such as solar PV, battery storage and double glazing are reaching a cost-effective price point.
In terms of the regulatory framework, there are policies emerging at a state and individual city level that commit jurisdictions to emissions reduction targets, Chapa says. These policies are likely to require an increasing proportion of residential stock to operate at net zero.
Chapa points out net zero also has benefits for utilities in terms of reducing the need for investments in the grid and other infrastructure.
“There are a lot of social benefits,” he adds.
A “big question” when it comes to net zero is examining the role of natural gas in homes that commonly use it for hot water and cooking.
“I can foresee a trend of the industry moving more to deliver fully-electric homes,” Chapa says. The challenge here for builders will be becoming accustomed to the design and delivery process for all-electric.
Chapa claims as part of this, builders also need to be considering how to ensure homes are electric vehicle-ready, as the uptake is expected to rise substantially over the coming years.
Overall, the design, whether it is a volume building floor plan, a multi-residential building, or a bespoke custom home, needs to be matched with a construction methodology that allows a project to be built with “fewer mistakes” in the form of gaps, poor sealing, thermal bridging or challenges to achieving continuous insulation.
Chapa says to sell the concept of net zero to home buyers it is important to speak to what they experience. That means promoting the benefits—not the buzzword—such as having a home that is resilient to the climate, future-proofed for EVs and against energy price hikes, healthier and affordable to operate.
“There is power in those statements,” Chapa says. “People are prepared to pay for amenity, quality and luxury. The challenge is how do we create coolness around having a home that is not trying to actively kill you in summer?”
renewable energy sector
net zero homes
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