A warm welcome

A certified passive house, this Dunedin home stays at a comfortable temperature year-round while needing very little energy to operate.
Words Kim Dungey Photos Otago Daily Times

Architect Rafe Maclean and his family have taken a while to adjust to the warm, dry conditions inside their Dunedin passive house. 

Before moving in, they spent two years in a cold rental property, where the heat pumps were on year-round and they slept with several blankets on each bed. 

In their newly built Maori Hill home, the indoor temperature is always  20–23 degrees and their energy bills are low thanks to the extremely airtight building envelope and the high-spec triple-glazed windows, insulation and heat recovery ventilation system. 

The family have swapped woollen tops for T-shirts and shorts, and often sleep under only a sheet. 

“Living in the house, we’ve become quite sensitive to the temperature,” Rafe says, smiling. “If it’s sitting at  

20 degrees, everyone’s thinking it’s a bit chilly and putting on jerseys.” 

Two asthmatic members of the family who are sensitive to mould, damp and pollen have not had any problems since moving in, and all of them enjoy not having to think about fresh air, temperature and humidity. 

Corrugated cladding provides a crisp contrast to the green surroundings.

“Here it’s all controlled and we have much more energy to do other things. We’re not scrambling over a fireplace or chopping wood or adjusting heaters.” 

Developed in Germany and applying to all kinds of buildings, not just houses, the passive house standard results in homes that use about 90 per cent less heating energy than existing buildings and 75 per cent less than an average new build. 

Rafe, who designed the South Island’s first certified passive house in Wanaka in 2015, says it is not only focused on energy efficiency. It also produces indoor environments that are quiet, comfortable and have excellent air quality. 

Kowhai House, named after a native tree on the site, is perched high on a hillside overlooking Leith Stream. 

No one else was brave enough to build on the steeply sloping plot, which drops away about 50m from the top and has a no-build 5m-wide council wastewater easement running through the only flat area. But where others saw only pitfalls, Rafe saw potential: the section faced northeast, it was near his daughters’ high school, and his 20-plus years as an architect had given him the skills to address the site’s challenges. 

Because of the difficult access and marginal soil, the three-bedroom home was designed to be simple in form and “buildability”. The shape is a gabled rectangle but with one face of the gable roof sloped up from the ridgeline, not down, to provide internal space for mezzanine beds. 

The simple form also makes the home more thermally efficient: compared with a more complex design with lots of corners, there is less envelope surface area through which heat can escape. 

With 70sqm on each of the two floors (including walls), the home is compact but big enough for the four family members to live together and still have their own space. 

The inter-floor structure is exposed to give more height to the space under it, with wastewater lines and ventilation ducting carefully concealed behind a partial floating ceiling aligned with interior cabinetry. 

After designing passive houses for his clients, architect Rafe Maclean wanted to experience the benefits first hand.

Zincalume corrugate on the exterior provides a crisp contrast to the green surroundings, while yellow highlights inside and out are a visual salute to the kowhai that flowers outside the living area in spring. 

Interior finishes are warm and welcoming, and the extensive use of pine plywood includes a pale painted floor. 

“I’d always wanted a white floor but forgot we had a black dog,” he jokes. 

Prefabricated structural insulated panels (SIPs from NZSIP) provided good insulation and reduced the time that builders Stevenson & Williams were on site. 

The mechanical heat recovery ventilation system, which supplies fresh, pre-warmed air, is housed in a small utility room. 

In theory, the family needs a heater of just under 1kW to heat the house on a cold day. In fact, they have two panel heaters – one upstairs and one downstairs to spread warmth throughout the home – and these are 1kW because they couldn’t find smaller ones, Rafe says: “Dunedin just doesn’t sell them, it would seem.” 

In one of the coldest months last winter, the house used 540kWh, which was mostly for hot water, computers and appliances, not solely heating. The annual heating demand is 15.4kWh per square metre; installing photovoltaic panels on the roof would have offset this, but the panels would have been difficult to access for cleaning. 

The use of interconnected spreadsheets allows the performance of passive houses to be accurately modelled before construction and is based on climate data for each location. In Wanaka, where he also works, Rafe would typically specify more sun shading and more insulation.  

While the passive house standard is mostly a voluntary one, a growing number of European cities and districts are requiring that all new buildings meet it. 

Rafe says because the buildings use much less energy, it is one way to achieve climate change targets: “I think eventually all new buildings will have to be a passive house or something similar but it’s just a matter of time and education... It’s pretty exciting but very glacial in take-up speed.”