Justin O'Connor Builders

Comfort from the cold

The thick walls of this Lucaston rammed-earth house keep out the crisp winds and chills of the Huon Valley.

Photo courtesy Justin O’Connor Builders


Cass Proudfoot

The soft honey-coloured walls on this Lucaston home are not just a design feature. They are actually made of 45cm-thick rammed earth, designed to keep out the bitter cold of the Tasmanian winter.

In fact, the entire house has been designed for climate comfort, by HIA member Justin O’Connor. His business, Justin O’Connor Builders specialises in building energy-efficient homes, or German inspired passive houses around the Hobart area. Justin’s business won the HIA Tasmanian GreenSmart Sustainable Home of the Year in 2017 for this property.

Lucaston is a small town in the Huon Valley.

‘It is one of the colder places in Tasmania,’ Justin explains. ‘Being stuck in a valley brings the cool air down.’

It can get down to -5oC overnight in Lucaston, with a lot of frost and ice in the area. The build even saw a dusting of snow on the ground at one stage, and some heavy frosts.

But the finished property is cosy and comfortable in winter, yet stays cool in Lucaston’s warm summer months.

‘Lucaston in summer is warm for Tasmania,’ Justin says. ‘So the site has climate extremes.

‘The building performs amazingly well. It sits at 21oC almost the whole time. So it is working, and the owners are absolutely rapt with how comfortable they are in the building,’ says Justin.

The house did once reach 24oC inside, but that was on a rare 38oC day, and the owners admit to having a window open, allowing some warm air in.

For this property the thick walls, insulation, tripled-glazed windows, thermal breaks and an airtight weather-sealed roof have made all the difference. Justin believes it could be the most airtight house in Tasmania.

Justin O'Connor Builders
The home is cosy and comfortable in winter, yet stays cool in Lucaston’s warm summer
Photo courtesy Justin O’Connor Builders
Justin O'Connor Builders Photo courtesy Justin O’Connor Builders

As part of his work in low-energy housing, Justin O’Connor does blower-door testing, and the envelope of this building returned an air-change rate of .48 air changes an hour at 50 pascals. This is well below what is required to meet passive house standard.

‘This is very, very difficult to achieve,’ he says. ‘So it even surprised me. But we took quite a lot of care with the rammed earth and the junctures and the detailing. I don’t know of any other Tasmanian building that has tested lower than that. But there will be soon – we’re always trying to push the boundaries!’

Justin keeps up with a lot of passive house builders on twitter to follow the race for ever-lower air-tightness results. He also watches for developments and new techniques in passive house design.

One such development is the counter-battened roof structure used on the Lucaston house.

‘This is the way roofs are starting to evolve in Tasmania,’ he says. ‘It’s international best practice.’

The iron roof serves as a rain screen. Behind that sits a black membrane for weather proofing or sarking. A big part of passive house construction is to have the weather-tightness layer sealed and water tight. And Justin can guarantee that this one is.

‘We had that roof without iron for three weeks and we just continued working underneath because it was waterproof with no leaks,’ he says.

The counter-batten roof has thin strips that run down to the gutter on top of the rafters, and then the roofing battens sit at 90 degrees to those and the roofing iron is screwed to those battens.

The finished property is cosy and comfortable in winter, yet stays cool in Lucaston’s warm summer months

‘In normal construction you’d see the roofing membrane go on top of those battens before the roof goes down. It’s the way we’ve done it over the years, which is now not the best way to be doing it – we learn and take notice of what’s happening internationally, and currently there’s a bit of a shift,’ Justin comments.

So, is a passive house more expensive? Justin O’Connor doesn’t think so, although the research is still coming in. More care does need to be taken with air tightness and with thermal breaks where surfaces meet, which can add a little time to a build.

Justin believes that the cost increase, to build a sustainable building in Australia is from around three per cent up to about seven per cent extra, on top of the total cost for a standard building.

‘We’re still gathering data – initially these types of buildings were mainly constructed in the high end of town, so it’s very hard to gauge how much extra they cost when you’re looking at million-dollar builds. But we have seen really good case studies in Victoria, with construction of certified passive houses for under $2000 per square metre.’

As well as airtightness, it’s important to have a thermal break between inside and outside. So the 45cm-thick walls have a layer of strong extruded polystyrene (XPS) in the middle. But otherwise the outer wall is identical to the interior walls.

‘The outside and inside walls are unpainted – what you see is the rammed earth,’ says Justin ‘They were built and finished at the start of the construction.’

Justin O'Connor Builders Photo courtesy Justin O’Connor Builders
Justin O'Connor Builders
Justin O’Connor embraces new techniques in passive house design, including the counter-battened roof structure used on the Lucaston house
Photo courtesy Justin O’Connor Builders

The earth walls were constructed from local gravel and sand. The house has a concrete slab with Hebel bricks around it, and the walls sit on the Hebel bricks. This is another way to create a thermal break.

‘Because that outside skin is going to get cold and warm we don’t want that energy to transfer though the insulated slab and into the building. So it reduces that thermal bridge,’ say Justin.

Twenty years ago when Justin O’Connor started out in the building industry in Hobart, not many people were looking for a sustainable home or passive house. Justin had to go to Melbourne to learn more about them, where an international trainer provided intensive training for the Passive House Institute of Germany. But now demand is growing strongly, and Justin himself is a director of the Australian Passive House Association.

Justin only works on low-energy houses with his business Justin O’Connor Builders, and is currently building a certified passive house for his own family.

‘We keep pushing the envelope with design, and what you can do,’ he says.

It will be fascinating to find out the energy rating that his own home will achieve, and the air-change rate per hour. Can he top the low-energy success of this Lucaston home?

‘We’re hoping to move into that as soon as possible. But as builders would know, building a house on the weekend takes a little bit of time.’

It seems that this eco-builder isn’t so different to more traditional builders after all.

Lucaston House at a glance

Energy rating: 8.7 stars
Cost: Around $700,000. Additionally the owners supplied key items such as the oven
Time: 10 months
Walls: 450mm rammed earth walls with 100mmXPS core (by Unique Earth Tasmania)
Roof: Proclima Mento 3000 Connect roof membrane (sealed weathertight layer) under counter-batten roof, Colorbond corrugated iron above
Windows and doors: Unilux triple glazed windows and doors (average U-0.8) with airtight installation

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