How Australia’s largest residential volume home builder designed and built its first Zero Net Carbon (ZNC) home
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Name of the home: Delta 29MR
Estate: Kaduna Park Estate
Address: 4 Mortlake Drive, Officer South
Retail pack: Energy Saver Plus pack
Home builder: Metricon Homes
Land developer: Parklea Developments
Size of home: 232m2
Retail cost (as displayed): $364,265
Estimated annual savings: $1522
Estimated cost to consumer: $21,150 (aluminium windows) – $28,090 (timber windows)
Estimated annual greenhouse gas savings: 105% or 7tCO2-e
Table 1: Annual energy and carbon emissions savings of 4 Mortlake Drive (ZNC home)
NatHERS rating: 6.6 Stars
Victorian Residential Efficiency Scorecard: 7
Carbon status: zero net carbon
Metricon Homes opened their first ZNC home on Sustainable House Day in September 2019, a four-bedroom 232m2 home, the prototype for an entire new range of home upgrade offerings. Metricon, Australia’s largest residential volume home builder, joined Sustainability Victoria’s ZNC Homes program to get support for the design, construction and marketing of high-efficiency, low-emission homes.
“Metricon’s consumer research has showed us that homebuyers are willing to spend a little more for a home that is more energy efficient, more comfortable and helps reduce their energy bills. We worked with Sustainability Victoria’s ZNC Homes Pilot Program to modify some of our home inclusions and are really pleased with the outcome, the Energy Saver Plus pack, which makes these types of homes accessible to new home buyers in Victoria,” said Peter Langfelder, Metricon’s Victorian General Manager and Director.
Metricon’s display home in Officer South, Victoria was designed to run on a combination of electricity and gas, with the homes emissions fully offset by renewable energy generated on-site.
The home was a vital step in Metricon now offering their Energy Saver Plus pack, a ZNC upgrade, to most home designs they offer in Victoria. Metricon’s move shows that you do not have to choose between good design and sustainable inclusions.
“At Metricon, we are always looking for ways to innovate and meet market demand for change," he said.
Working with Sustainability Victoria has allowed us to test home inclusions that when bundled together, not only offer our customers cost savings, but are also a win for the environment.
Peter Langfelder, Metricon’s Victorian General Manager and Director
Metricon’s Delta 29MR home was an existing design, which was modelled for an increase to the NatHERS rating from 6 to 6.6 stars. The home was then modelled for ZNC. The aim was to create an affordable and comfortable zero-emissions home.
Upon joining the ZNC Homes program in late 2018, Metricon developed its Energy Saver Plus pack with assistance from Sustainability Victoria, using the ZNC Modelling information.
The 232 square-metre home includes four bedrooms, two bathrooms and two living areas and is the perfect home for a family of four. The retail price of the display home including the upgrade package with timber windows is $364,265. The ZNC upgrade cost represents 7.7% of the total home cost.
The display home achieved a 6.6 stars NatHERS rating, which is 0.6 stars above the National Construction Code’s minimum star rating for new homes. This makes the home cheaper to run as well as more comfortable to live in.
Due to other site constraints, one challenge for this home was that it had a southerly orientation of the main living areas, which featured large windows to allow natural light to flow into the areas throughout the year as well providing access to an outdoor living area.
A southerly orientation is a challenge because it reduces the amount of sun that comes into the home during the winter months. Analysis showed that the difference between simply having the living rooms facing north rather than south for this home design made a difference of 0.3 stars in terms of the NatHERS rating. The challenge was solved with extra insulation in the roof, double glazing to most windows and extra insulation in the walls.
Apart from ensuring that the home had a comfortable thermal performance it also was built with attention to air tightness, LED lighting, energy efficient fixed appliances and a roof solar PV system.
The building shell design includes:
The fixed appliances include:
Comparing the ZNC home design to the standard Delta 29MR home design, the benefits include superior build inclusions, increased comfort, less environmental footprint and reduced energy costs.
The table below compares the Metricon ZNC home design with a standard home design:
Standard homes with a 6 Star NatHERS energy rating, insulation meeting only basic NCC requirements, no double glazing and no post construction ABV testing, are often colder in winter, hotter in summer, noisier, more draughty and more likely to allow dust and pollen into the home, making these homes much less comfortable and healthy to live in.
By comparison, the indoor ‘feel’, temperature/conditions of 4 Mortlake Drive, Officer South is comfortable no matter what the weather conditions outside the house. Modelling data also shows that the home, if left unheated and cooled would have less hours outside the comfort range between 18–26°C.
During the launch of the home in September, no heating had been provided overnight and the home still felt comfortable when staff arrived to set up.
Metricon’s display home in Officer South was constructed over a six-month period.
Care was taken in construction of the building shell to produce a high level of air tightness, so that occupants are less reliant on using energy for heating and cooling, which accounts of up to 60% of home energy use.
To produce high levels of air tightness, extra care is taken during to install the insulation to realised air leakage, in particular around the window frames and the openings for services such as the air-conditioning. Silicone sealing between the slab and frame was applied and a sisalation wrap was installed with care taken to realised tears and gaps.
Additionally, draught sealed exhaust fans and weather strips were installed for further draught proofing. Finally to ensure that moisture would not build up in the wet-areas, these areas operate automatically measuring when moisture builds up and releasing the moisture directly to the outside.
All venting from the kitchen and the wet rooms vent directly to the outside rather than into the roof cavity – further avoiding the risks of mould and mildew.
To verify that the Metricon display home met the ZNC Homes standard, an independent As-built verification (ABV) check was undertaken to ensure that the original design intent had been realised in the build.
This verification check included two checks:
Blower door/window test
The home was blower-door tested to determine that the air leakage rate complies with the ZNC Homes program standard of not more than six air changes per hour. The home passed the blower door test with an airtightness of 5.1 air changes per hour. The standard requires a rate of between three to six air changes per hour. If the home falls below three, mechanical fan heat recovery ventilation is required to ensure adequate fresh is available to occupants.
Acceptable range: Air permeability of between 3.0 and 6.04 Mortlake Drive, Officer South: Air permeability of 5.1
This test uses a special camera that can ‘see’ through the home’s interior walls to check that the insulation behind the walls and ceilings has been correctly installed and that no more than five per cent of insulation is missing. The display home passed this component of ABV if insulation coverage achieves greater than 95% coverage.
Zero Net Carbon Home maximum allowed: 5% missing insulationMetricon’s 4 Mortlake Drive home: 1% missing insulation
Research shows that when marketing a sustainable product there is a substantial amount of customer confusion in the market and it is not clear to the customer what the benefit is to them. Metricon has shown a clear understanding of their market segment by communicating clearly what the consumer benefit is. The display home therefore contains plaques that show what the benefit is for the customer and not necessarily for the environment.
By building the ZNC home and offering this product as an upgrade to any design they have on the market, Metricon has shown that it is ready to lead the volume home construction market in the future and that they are ready to meet the challenges a carbon emission free future may pose.
“We have seen an enquiry and purchase trend emerging in our regional Victorian business which is interesting. Arguably this customer is more aware of Victoria’s extremes in temperature and the effect a thermally efficient home has on living quality and utilities bills. We will be looking to strengthen knowledge of the Energy Saver Plus pack and its benefits across all of our Victorian consumer markets in 2021", said Peter Langfelder.
Metricon has opened a second ZNC display home in Mickleham in Melbourne’s North, and ran a competition to provide the upgrade to three lucky winners of the Energy Saver Plus packs. The competition received 200 applicants, demonstrating that there is an interest in the product.
When the Delta 29MR was launched it attracted media attention with a reach of over 2 million. This home has started a conversation around the creation of an environmentally conscious product that can be offered to the mass market and essentially becomes an easy option. Metricon and Sustainability Victoria have done all the thinking so the customer doesn’t have to make the difficult choice between good design and a comfortable home – it is all done for them.