Very Low Carbon Habitat

The Passive House concept promises low-carbon living that doesn’t cost the Earth, and the way it is gaining ground around the world demonstrates that such claims are far from being so much hot air

Since the first ‘prototype’ was developed in 1990, the Passive House concept of energy efficient buildings has been gaining ground across the world – literally.

There are now over 30,000 buildings that are recognised as fulfilling the required criteria, covering a million square metres of space. That may not be much in the grand scheme of the global built environment, but it represents the steady growth in the construction of certified Passive House structures.

The millionth-metre mark was achieved last year with certification of a detached house in Santa Cruz, California, in the United States. The Midori Haus, as it is known, gained its certification from the Passive House Institute (PHI) in Darmstadt, Germany, in December 2014. Given the symbolic threshold this property crossed, the institute issued a special – what you might call a commemorative – certificate to recognise the achievement.

Originally built in 1922, the Midori Haus is a three-bedroom, two-bathroom single-storey property. It was remodelled in 2012 to the Passive House Standard. The house retained the original foundation, floor, framing, porch, built-in furniture, as well as the interior trims and accents. Since the work was completed energy usage has been monitored, with utility bills showing that the energy consumption dropped by 80%.

California’s climate, of course, is somewhat removed from that of Central and Northern Europe, where the Passive House concept was first devised, but it is a concept that has been tailored to – and been realised in – a variety of different climates in the 25 years since the first building tested out the principles. These days, Passive House structures are to be found on almost every continent and in practically every climate zone.

Most Passive House structures – they aren’t exclusively residential properties – are located in Central Europe, and despite the quantified number of such buildings, the real number may be much higher, according to the PHI.

That’s because for one thing, it exists to widely disseminate its research into the concept and methodologies for putting it in practice, for another certification is voluntary. Consequently, the existence of Passive House buildings may be far more widespread than even its progenitors realise.

“In principle, anyone can build a passive house,” said Zeno Bastian, the PHI’s head of building certification. “What matters is compliance with the clearly defined criteria for energy consumption. How this is achieved depends on climate. In Central Europe the most essential measures include thermal bridge free construction, an airtight building envelope, a ventilation system with heat recovery, triple-glazed windows, and excellent thermal insulation.

“The primary purpose of certification is quality assurance. With this internationally recognised seal, building owners are safe in the knowledge that the desired savings for heating costs and added benefits of a Passive House will actually be realised.”

The Passive House concept – or ‘passivhaus’ to give its European flavour – was devised by Professors Bo Adamson of Sweden and Dr Wolfgang Feist of Germany, with the ‘prototype’ constructed in Darmstadt. The Kranichstein Passive House, as it is known, was Europe’s first multi-family house to achieve a documented heating energy consumption below 12kWh/ (m2a).

Since then, the concept has taken root with Passive House structures constructed in every European country, with Australia, China, Japan, Canada, the USA, and South America joining in to put the concept through its paces. Apparently, there’s even a research station in Antarctica built to the Passive House standard, according to the PHI.

These days, when branding is King – or at least courtier – it is important to note that Passive House is not a brand, nor is it linked to any specific type of construction; both are important points in maintaining the flexibility and adaptability of the principles, as much as its ‘open source’ nature, whereby anybody can access the research of the PHI and its sister bodies around the world, and work on its own enhancements to the concept.

That doubtless helps to explain its growing global appeal and the diversity of projects to which it has been applied. To date, according to the PHI, the largest building built to the Passive House standard is an office tower in Vienna, Austria. The RHW.2 building has a useable area of almost 21,000 square metres. Conversely, the smallest certified Passive House is a building near Rennes, France, which has a floor area of just 11 square metres.

Then there’s Heidelberg’s Bahnstadt quarter, which is billed as the world’s largest Passive House district. At the International Passive House Conference last year, it scooped the 2014 Passive House Award for its “exemplary nature”.

An award plaque now adorns the district’s Schetzinger Terrasse kindergarten where passers-by can see this reminder of the area’s international recognition.

“The award displays strikingly the pioneering spirit demonstrated by the world’s largest Passive House neighbourhood,” said Heidelberg’s mayor, Dr Eckart Würzner during the plaque’s official unveiling last year. “The Bahnstadt district is gaining ever more attention internationally and is visibly asserting itself as one of the most innovative urban development projects of our time.

Our newest city district shows what is possible when existing technical opportunities are intelligently employed and is a source of pride.”

According to Dr Feist, who is director of the PHI in Germany, the district more or less unveils a view of future urban living. “High energy performance construction is establishing itself in an increasing number of countries,” he said. “An entire city district built to the Passive House Standard, however, is until now unique. In this way, the city of Heidelberg is delivering a blueprint for the future. The European Buildings directive dictates that so-called Nearly Zero Energy Buildings are to become the norm by 2021. With the Passive House Standard, Bahnstadt is already fulfilling these requirements.”

Here in the UK, the Passive House approach is also finding converts, although it’s fair to say the uptake has lagged somewhat behind the Continent, given the home-grown ecotown concept and then subsequently the Code for Sustainable Homes that sought to provide a framework for the Government’s zero-carbon ambitions [Since writing and original publication the Government has scrapped the Code]. Nonetheless, the UK has joined the global Passive House club, as it were.

Hastoe Housing, for instance, created its first Passive House development in Wimbish. In October last year the organisation released the findings of a two-year evaluation of the performance of the 14 “exemplar” homes. The assessment, supported by the University of East Anglia and the Technology Strategy Board, gave a welcome verdict for Hastoe – that the homes had performed as designed and delivered vastly lower heating bills for the residents.

“Given that this was the first Passivhaus development by Hastoe, the first Passivhaus design by the architect, and the first Passivhaus construction project by the contractor, in essence making it an experimental project for all three, these findings are remarkable and demonstrate that Passivhaus provides a viable and successful route to low-energy living,” the evaluation report noted.

Wimbish is a rural development, but Octavia Housing has created an example of a Passive House scheme in an urban setting with Sulgrave Gardens in Brook Green, Shepherds Bush, London. The 30-home mixed-tenure scheme was intended to show that the concept is indeed a viable proposition in the higher density of UK towns and cities.

“As in many urban dwellings, Octavia and our team of partners were faced with constraints that exist as part of the usual planning and local contextual considerations, and as an added complication the site is sandwiched between two conservation areas. This coupled with the desire to build a mixed-tenure scheme of such a scale as well as being guided by the Passivhaus principles, required new dimensions of innovation,” the organisation said.

Low carbon living is essential to help turn the tide of climate change, and that’s precisely why Passive House is gaining ground, but there’s another important reason too – and that’s in the wallets of the occupants.

Perhaps it’s fitting, then, to leave the last word on this to the concept’s founder, Dr Feist: “Passive House components allow building owners to save hard cash.”

Anatomy of low-carbon living

• In Passive Houses savings of up to 90% can be achieved on the energy expenditure required for space heating or cooling compared with “typical building stock” and over 75% compared to average newbuilds. They use less than 1.5 litres of oil or 1.5m3 of gas to heat one square meter of living space for a year, said to be substantially less than common ‘low energy’ buildings

• Passive Houses use the sun, internal heat sources and heat recovery in such a way that make conventional heating systems unnecessary, even during the coldest of winters. During warmer months, they make use of passive cooling techniques such as strategic shading to keep them comfortably cool

• Internal surface temperatures vary little from indoor air temperatures, even in the face of extreme outdoor temperatures. Special windows and a building envelope consisting of a highly insulated roof and floor slab, as well as highly insulated exterior walls keep the desired warmth in the house, or undesirable heat out

• A ventilation system discretely supplies constant fresh air, maintaining air quality without unpleasant draughts. A highly efficient heat recovery unit allows for heat in the exhaust air to be reclaimed and re-used

(Source: Passive House Institute, Darmstadt, Germany)

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