St Clair Certified Passive House

By Architype

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St Clair Certified Passive House banner
Project by
Year of completion
2019
Project cost
$0.5m - $1m
Building style
Passive

Overlooking St Clair beach, Dunedin’s popular surfing spot, this modern black pavilion is a sustainable certified passive house with a sunny outdoor living room that is cantilevered over a steep and challenging site.

Dissatisfied with the quality of many of the houses they found on the market in Dunedin, a family who had previously lived in a well-insulated, centrally heated home in the UK were eager to build a passive house that would be comfortable, healthy and energy efficient year round.

From the start of the design process, the architects faced a number of challenges that implicated each other. They needed to capture views over St Clair beach to the east, make the most of the solar gains from the north, and work around a steep site set close to the road. The sunniest part of the site, at the northern corner, was the most obvious place for outdoor living but it was also the most sensible place for cars to access the property and situated right below the street, leaving little privacy.

“It was a little tricky to make the design work,” explains Architype’s Tim Ross. “There is also a very tall house to the north which shaded the house for much of the day. We decided to raise the house as high on the site as possible to allow the main outdoor living space to look down on the street. We added movable shutters to create a private yet sunny outdoor living deck that captures the the sun and views throughout the day, without interference from cars accessing the property.”

Along with a cantilevered outdoor area that hangs out over the bush, the height of the foundations and retaining walls have been minimised to create a relatively economical solution on this very steep site. “With a passive house, ideally you want to keep the thermal envelope of the building reasonably compact. This doesn't mean you have to end up with a boring building form though. Often, you can play with those parts of the building that are outside the thermal envelope (garages, decks, etc) to articulate the building form and, from a thermal massing point of view, a compact form makes it easier to build and to heat,” says Tim. 

However, the overall result is a decent-sized four-bedroomed family home that nods to mid-century modern designs with its black pavilion form, exposed rafters, cantilevered terrace and low roof profile that draws in the western afternoon sun. The main living areas are located on the upper level, with a guest bedroom, service areas and garage downstairs. And, because street parking in the area is limited, extra parking has been added on the upper level.

To be certified as a Passive House, the building needed to have a maximum heating demand of 15kW per m2, per annum. This requires a clever balancing act during the design stage to keeping the house well-insulated and draft-proof, with quiet mechanical ventilation drawing in fresh air and expelling warm, stale air to create an even temperature of 20-22 degrees celsius all-year-round.

When considering building a passive home, potential homeowners are often confused about the idea of ‘airtightness’, which makes the house sound like it will be stuffy. But the principal is to basically to eliminate the leaks and gaps around a house, where warm air escapes, and to control the rate of ventilation to ensure a warm and comfortable home. “It’s not a hermetically sealed box – you can still open the windows on a nice day,” says Tim.

“The system is more about being draft-proof rather than airtight,” says Tim “If you have a house that leaks air, when the wind is blowing outside, then you can’t control the leaks. With a passive home, you actually prevent any leaks. The warm air is expelled and the heat recovery ventilation system essentially jumps the heat over into the incoming fresh air to create an even temperature. But, it’s not like a ducted heat pump system that moves huge volumes of air; with this system, you can’t hear it or feel it.”

“We do our own testing for draftproofness,” explains Tim. “During the build, once the envelope is completed, we attach a large fan to the front door and pressurise and depressurise the house to 50Pa and, then, monitor any leaks so the builder can address them. It’s much easier to do this on a cold day because you can run your hand around the junctions of materials or services penetrations and feel the jets of cold air on your hand where leaks are present.” To create the draft-free building envelope, the architects used a special membrane and tapes, along with triple glazing and thermally broken windows.

To model the energy performance of the house, the architects used the Passive House Planning Package, which runs as an Excel spreadsheet and is able to accurately predict the energy consumption and comfort of the house depending on the design, materials and product specifications you enter. It factors in the performance data, such as occupied floor areas, insulation, window sizes, types of glazing, thermal bridging and so on.

“It’s a great tool,” says Tim. “As you work through the process, it tells you if you will achieve the standard and is the backbone to the entire certification process. It is a great quality-control process and ensure that you can't fudge your numbers. The builder also has to photograph key aspects of their work throughout the build process and sign a declaration, which is a legal document, that helps protect the integrity of the certification.”

In many countries, passive house certification is becoming more and more popular because this scientific building process, which originates from Germany, ensures the health and comfort of the tenants, as well as reducing the energy costs of a home. Overseas, the data suggests that passive houses can sell for five to ten per cent more than a regular house, justifying the extra investment from the start.

“For the owners of St Clair House, they were mostly looking for comfort and quality,” explains Tim. “There is a level of comfort that you can achieve with a Passive House that you just can’t achieve with a code house, no matter how much heat you pump into it. Here, the temperatures are very even with no cold spots, which can result in condensation and mould.”

In the future, low-energy houses like St Clair House will have to become the norm in New Zealand, as our electricity supplies are leaned on more for infrastructure and industry and, also, to meet our national zero-carbon targets. “New homes like this are relatively easy to design to high energy standards, whereas completely retro-fitting houses is more challenging” says Tim. “We cannot continue to build homes that place huge demands on our winter electricity supply. In the summer, we are okay but, in the winter, we will struggle to decarbonise our grid if we don’t reduce energy consumption from our buildings.”

 

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About the
Professional

Architype is an award winning architectural practice specialising in the design of high performance Passive House and low energy residential and community architecture.

OUR APPROACH

At Architype we believe that good design is worth the effort. We know that building is expensive and to us it just makes sense to put the effort in at the design stage to carefully think through the design and develop solutions which, once constructed, will provide a lifetime of delight for the building users.

We also know that, “delight” is more than just good space planning and elegant building form, it is also about the long term and comfort and energy efficiency of the building. At Architype our focus is on creating buildings which provide warm, healthy and affordable environments for building users.

Comfortable and low energy buildings can’t be created by bolting on solutions at the end of the design process. When understood properly these factors will influence almost every key decision in the design process.

WHAT WE DO DIFFERENTLY

At Architype, in addition to considering important traditional architectural issues like: context, views, town planning, entry, public and private space, circulation and orientation, we add additional design considerations to the mix. These include: favouring compact building forms, appropriate distribution and shading of windows, continuity in insulation, draught proof construction, thermal bridge free detailing and strategies for the simple distribution of ventilation ducting.

We believe that an understanding of building science and a passion for good design should go hand in hand.

Our projects employ a range of high performance building systems and components including high performance timber framing, various types of structural insulated panels, insulated concrete forms, uPVC windows, European timber windows and ventilation systems with heat recovery.

We love to work with clients who are informed and see the value in building better.

BUILDING INFORMATION MODELLING

With highly integrated design comes the need for powerful tools for the development and communication of projects. All our projects are modeled using Building Information Modelling software or BIM. Using this powerful software a virtual model of each project is created from which all of the drawings are derived. Change a door on one drawing and it changes in every drawing. As the project progresses from the initial concept design to detailed design, more and more information is added to the model creating a more and more complete reflection of the final building. We are able to export files to our clients who can explore the design in 3D on their own computer or tablet. More than ever before this has allowed our clients to visualise and understand their projects before any work begins on site. Not only has this improved communication but it also results in fewer changes on site.

We can also leverage the digital model to quickly create additional deliverables like sun studies, energy modelling, schedules and promotional material.

At ArchiPro we recognise and acknowledge the existing, original and ancient connection Aboriginal and Torres Strait Islander peoples have to the lands and waterways across the Australian continent. We pay our respects to the elders past and present. We commit to working together to build a prosperous and inclusive Australia.