Warren McLaren reports on Harmony 9, which is considered the first 9 star home built in Australia by a commercial developer.
The four-bedroom, two- storey, 296 sqm house can be found at the Waverley Park development in eastern Melbourne. Here the Mirvac Group is building up to 1,500 houses on the site of the old Australian Football League (AFL) stadium and carpark.
Ironically, one of the key reasons the AFL moved back to the city was the lack of public transport infrastructure to Waverley Park. Yet it is here which Mirvac Design, the architecture and design subsidiary of Mirvac, has showcased its sustainability credentials with a prototype house.
We asked John Eckert, national housing director for Mirvac Design, why it elected to shoot for a 9 star home. It turns out it was a strategic decision to anticipate how the company might respond to pending changes to the Building Code of Australia (BCA), seeing what energy efficiencies could be achieved through existing construction methods and materials available to its project partners.
After COAG (Council of Australian Governments) meetings in 2009, the federal, state and territory governments set out to develop what they termed a National Building Energy Standard — Setting, Assessment and Rating Framework. The aim was to strive for a consistency of energy ratings for residential and commercial buildings across the country.
The Nationwide House Energy Rating Scheme (NatHERS) uses AccuRate computer software to score a residential home for its thermal comfort. The scale extends from zero to 10 stars, with the latter achieved when residents do not ever require the use of artificial cooling or heating. Furthermore, COAG’s $88 million National Strategy on Energy Efficiency (NSEE) proposes, amongst other initiatives, that it wants “…Australian homes to provide energy, water and greenhouse performance information to buyers and renters, starting with energy efficiency in 2011.”
Indeed, this practice has been common place in the Australian Capital Territory (ACT) since 1999. A study completed for the NSEE found that increasing the energy efficiency rating in a detached house in the ACT in 2005 with a price value of $365,000 by 0.5 stars would be associated with an additional cost of $4,489.
As one of Australia’s major residential property developers, Mirvac has plenty of commercial reasons for exploring its opportunities for building houses with optimal NatHERS ratings. But before a single sod was turned or a nail hammered, Mirvac sat down with Floyd Energy to, as Eckert put it, “test the limits of computer modelling”. They were, he says, “trying to ‘break’ the software”.
Initially they thought they might be able choose between either installing double glazing or fully insulating the external walls, but the modelling surprised them, indicating they’d need to do both. According to Eckert, “moving from 5 stars to 6 stars is relatively easy. Well, not easy, as such, but is largely common sense. Achieving a 7 star rating is harder again, but from 7 stars to 8 stars requires an even more substantial commitment.”
After exhaustive computer modelling trying umpteen permutations of design, construction methods and material types, Mirvac Design came up with a house rated to 9.2 stars. Could it have pushed the design envelope out to a full 10 stars? Eckert is dubious.
As it is, Harmony 9 is expected to passively maintain a temperature range of 18°C to 24°C for 98 per cent of the year, with window shading arranged so no summer sunlight penetration is expected between the four hottest months of the year — October 17 to February 26. For those remaining few days, a need for artificial cooling or heating is anticipated and provided for by a small reverse cycle air- conditioning system.
Yet achieving a high energy efficiency rating wasn’t the only challenge that Mirvac Design set itself. With over 23,000 housing lots to develop nationally, the company has long-term partnerships with suppliers and contractors that are worth retaining, so the Harmony 9 house needed to use products and materials currently available from its suppliers in the Victorian residential construction market.
To reduce the cost of prototyping, Harmony 9 also earns its keep with a day job as Waverley Park Development’s sales office. And just as features from concept cars trickle down into production models, so too are aspects of Harmony 9 being incorporated into Mirvac’s 6 star homes.
How then does Harmony 9 achieve its extra 3.2 stars? Partly by reverse brick veneer construction, which is the complete inverse of current Australia housing. Brick has thermal mass, slowly absorbing radiant heat and later releasing it. Traditional, uninsulated brick veneer homes suck up the heat of a searing Australian sun and re-radiate that warmth into the house in the late afternoon/evening. (According to NatHERS, prior to 2003 less than 1 per cent of Australian houses would achieve a 5 star rating, with the average 1990 house managing just 1 star.)
Keeping the brick inside, protected by a lightweight, highly insulated external wall and roof (R5 insulated external walls and R8 insulated galvanised steel roof), moderates the temperate, reducing the need for summer air- conditioning. This effect is enhanced by resident-adjusted cross-flow ventilation from doors and windows. Any warm air inside can be further vented out through a thermal chimney that rises through the centre of the two-storey building.
Eckert freely acknowledges the operational vagaries of user-adjusted passive solar design — the “1 star resident in a 9 star house”, he calls it.
The shades that block the northern summer sun doubles as platforms for the grid-connected 3.6 kW solar voltaic system, which is more than enough to power all the electricity needs of the house. A gas-boosted solar hot system is similarly sited.
Inside the front door is a green switch allowing residents to turn off dedicated appliances with one click as they leave the house. Beneath the driveway a 20,000 litre rainwater tank is hidden and combined with a class A recycled greywater system to water the garden, flush toilets and do the laundry.
It has been calculated that Harmony 9 will annually save 12.047 tonnes of CO2 and 125,0000 litres of potable water, providing residents with over $1,200 in reduced energy bills.
But it is not all good news on the savings front. Although Eckert would not say how much Harmony 9 might sell for (it may be put up for auction once the Waverley Park development is completed), he did indicate Harmony 9 was worth three times that of its four-bedroom 6 star houses on the site. At the time of writing, one of those houses was going for $780,000, so auction goers will need a rather fat wallet.
Space unfortunately precludes us from covering the myriad of other ecodesign attributes of Harmony 9, so we suggest contacting Mirvac for its very comprehensive Harmony 9 data sheets. Yet it is worth stealing a line to record that Mirvac’s Eckert observed that even this groundbreaking project was “but a poofteenth [infinitesimally small] way along the road to true sustainability.”
