Developing Affordable Passive Houses

by Sophi MacMillan

A new house in a Melbourne suburban street has demonstrated that affordable Passive House construction looks within reach in Australia.

Until now passive houses were priced well beyond the means of ordinary Australians, and scared off both builders and home buyers.

But retirees Sue and Peter, builder RMH homes, passive house certifier Grun Consulting, and uPVC windows supplier VUE Windows have produced an elegant, spacious home that looks like any normal new build. Unlike those normal new builds, however, the home will produce stellar results in terms of thermal comfort and energy efficiency. In doing so, they have opened the door to more affordable, comfortable, high performing homes in Australia.

The passive house - or Passivhaus - movement started in Germany in the 1980s, and worldwide there are now around 30,000 certified to strict Passive House Institute requirements, with a further 60,000 residential and non-residential units applying the principles, according to the UK’s Passivhaus association.

In Australia, there are only 10 certified passive houses, but interest is growing.

“Passivhaus is all about taking a space and making it perform,” says Clare Parry, founder of Grun Consulting. “It provides an as-built guarantee. It was established to provide comfortable, healthy buildings. Excellent air quality and lower energy use are side effects.”

These results are achieved through orientation, layout and product selection, including high performance windows.

Until recently Australia’s energy has been cheap and the climate moderate. However, the Australian National University identified electricity prices between 2006 and 2016 rose over 100 per cent in Queensland, NSW and Victoria. The average annual electricity bill in Australia in 2015-16 was $1,296, and according to the Clean Energy Council, it is not uncommon now for people to pay over $2,000 per year. This is becoming exacerbated by more extreme weather, such as longer heatwaves.

According to National House Energy Rating Scheme (NatHERs), the average (unimproved) 30-year-old home in Australia would achieve just a 1 star NatHERs rating. This is largely due to air infiltration and poor insulation. And while the mandatory 6 stars for builds today is clearly better, NatHERs says it is not outstanding, condemning today’s new home owners to years of poor indoor comfort.

The Passivhaus choice

Sue did not set out to have a passive house, but she was fed up with both the draughty conditions of her apartment and the worsening traffic and noise of inner city South Yarra. Unable to find an existing property that met her requirements, she and Peter decided to build. They interviewed and obtained quotes from specialised passive house builders and ordinary builders. With dismay, they discovered that the typical price for a passive house build is between $3,000 and $5,000 per square metre.

Determined to fit a passive house within their more modest budget, Sue and Peter hired a traditional builder keen to give it a go. Drawing on their time and experience as owner-builders, their team achieved a passive house build – verified by certification – for a remarkable $2,100 per square metre.

“Our three-bedroom house is 250 square metres, same as the average new house. Our certified passive house is in the same price bracket as a luxury high-volume build in a housing estate and we are confident our house will perform better than 10 stars,” says Peter.

Orientation is obviously a major design consideration. Allied to this is then the placement, size and type of windows. Use of high performance windows - low emissivity, double or triple glazed windows with non-metal or thermally broken frames - is essential. We think about insulating our walls; we should do the same with our windows.

Sue’s house features an expansive wall consisting of 32.45 square metres of uPVC double glazed windows and doors across the north-facing living and kitchen areas, including openable fanlight windows at ceiling height for purging hot summer air.

The argon filled double glazed uPVC windows achieve excellent insulation value of Uw 1.37 and a solar heat gain co-efficiency (SHGC) of 0.58, allowing winter sunshine to penetrate but not too much solar radiation in summer.

According to VUE Windows, in a normal house, such a large wall of glass with only six-millimetre single pane glass would result in a poor insulation value of Ug 5.8 and high SHGC 0.82, making the indoors uncomfortably hot in summer and cold in winter, or excessively expensive to heat and cool. These figures are for the glass alone; metal non-thermally broken frames are likely to increase (that is, worsen) the window U values as they conduct the heat from one side to the other.

The floor plan is shaped like a big "U" and allows natural light into each room – carefully – with appropriate placement of windows around a courtyard with good eaves and shading. The total budget for windows and external doors was a little over $50,000. Although this constituted about 10 per cent of the budget, these were an integral design element to the house and will remain for a large part of the building’s life. Timber windows were found to be more expensive and require more maintenance than uPVC, which Sue and Peter were keen to avoid as busy retirees.

Meeting passive house standards also requires air leakage and thermal transfer to be carefully avoided. This was achieved with an air tight skin behind the plaster walls, no thermal transfer with the outside environment via structural frames, such as stumps, walls and window frames, no gaps through the insulation by cabling or pipes, and no air leakage around windows and doors. High performing windows like uPVC ones have continuous, built-in double sealing systems and multiple locking points to provide a tight seal between the sash frame and the house frame reducing air infiltration.

In order to control the movement of air and temperature, a heat recovery ventilation (HRV) system with a highly efficient heat exchanger is used. These lungs of the house operate 24/7 ensuring there is only filtered, comfortable temperature air.

To gain passive house certification, pressure tests are conducted upon build completion. Sue and Peter were delighted the house passed the tests with a low 0.6 air changes per hour (ACH). With the HRV, they have controlled and comfortable air at less than five ACH. A typical Australian house is so leaky it has 15 ACH, the equivalent of having a door open all the time.

Sue and Peter have built their dream home that will keep them comfortable for the rest of their days. They have also converted their builder and tradies to sustainable homes, and have forged a new future for sustainable, affordable living in Australia.

Sophi MacMillan

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