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Thursday, 24 November 2011

The Zero Carbon House – Dream or Reality?

Philosophically speaking, for anyone not completely without sympathy for this planet it should be both. However, life intervenes with planning departments, empty bank accounts and the question whether ‘zero carbon’ is more than a slogan.

Zero What?

In theory it is quite simple. The term describes residential and commercial buildings that generate and preserve as much energy as is needed by its inhabitants to live and work comfortably. The emphasis is very much on conserving heat with no or very little extra input required. In Germany it is called, therefore, ‘Passivhaus’ (passive house) because it provides warmth mainly by preventing it from escaping in the first place. Utilising additional sources, such as sunlight through large areas of glass or the heat emitted by inhabitants, supplementary, active generation is brought as close to zero as possible. Anything extra should come from renewable sources, for example, solar panels, ground source heat pumps, etc. This helps to keep the carbon dioxide (CO2) balance neutral.

Finnish Timber House (can  be used as Eco house)

Of course, when you start to pick at it the zero carbon claim falls apart. Just like electric cars whose credentials suffer if the fuel or electricity we have to feed them do not stem from renewables, a house contains parts, e.g. windows, the manufacturing of which is not carbon neutral yet. We have not reached the perfect stage but those of us equipped with a healthy dose of realism will celebrate the technology we have available now that allows us to take this massive step into the right direction. So what can this concept offer today?

The Sum of All Parts

The zero carbon principle rests on six elements

Airtight Shell

At first this sounds like living in a Tupperware box. However, the reasoning is simple. If air cannot come in through gaps, it cannot escape either and take heat with it. While this makes artificial ventilation necessary it provides the opportunity to control it in terms of flow, moisture content, contaminants and temperature, which brings us to the next point.

Air Heat Recovery

Fresh air coming in goes through a filter and then a heat exchanger passing the warm, outgoing air. That way a large part of the energy is preserved in the pre-heated influx.

Exclusion of Thermal Bridges

Nature always seeks the equilibrium. Therefore, if it is warm inside and colder outside heat will try to escape until an equal temperature is achieved. It will do this along the path of least resistance. Let’s say a wall is well insulated but, for example, has a steel girder in it that is in contact with the outer environment without insulation. The thermal protection of the wall is breeched and heat will escape along that bridge. In any low-energy building and especially zero carbon houses avoiding this is one of the most important parts of the overall design process. A positive side-effect is the prevention of inner surfaces that cool down and can cause dampness with all its related problems. The aim is a an almost perfect cocoon.


... is very important, therefore. Apparently, a passive house will be comfortable for up to four days after the heating system has stopped working with outside temperatures at below freezing. I live in a house built in the 1920s. A few years ago a winter storm interrupted our power supply. All of a sudden the old boiler became very environmentally friendly by not burning any fossil gas because the pump wasn’t working without electricity. Soon indoors everything turned pretty frosty, particularly our mood. We could only dream of several days in sustained comfort. In contrast the ultimate objective in a zero carbon house is to create a comfortable, healthy living space without the need of any additional heating whatsoever. That is where it takes the low energy building concept one step further.

Passive House Windows

These are a far cry from your run-of-the-mill double glazed items. Usually triple-glazed they also sport a well-insulated frame, insulated join between glass and edge, as well as thermally optimised fitting. Going back to an earlier point windows are heat bridges and have to be up to the insulation standard of the outer wall. Otherwise a lot of energy will be lost. Glass has a special role in that large glazed areas are designed in a way that they capture sunlight in winter, i.e. free heat, but still avoid turning the interior into an oven in summer.

Complementing Technology

The zero carbon house is a holistic concept, where several parts need to be integrated in order to make the sum work as perfectly as possible. The protective cocoon of the outer shell needs other components. I have mentioned the ventilation system already, which includes an air cleaner and heat exchanger. Others are

  • Renewable energy if needed
    • Ground source heat pumps
    • Air heat pumps
    • Solar panels (photovoltaic and water heating)
    • Bio fuels
      • Solid fuel burners
      • Gas from anaerobic digestion
  • Community heat
  • Environmentally friendly building materials
  • Environmentally friendly insulation materials
  • Grey water recycling
  • Rain water capture
  • Living/green roof

This list is not exhaustive but gives an idea of what is possible these days. The question is whether it is being put into practice.

Eco House_Model

What’s Happening?

The Informations-Gemeinschaft Passivhaus Deutschland (German Association for Information on Passive Houses) reckoned that in 2011 about 16,500 such buildings existed in Germany and twice that around the world. From the first passive house in Darmstadt Kranichstein, built in 1991, this is not as good as it could be but not bad either. Nevertheless, Germany is still at the forefront worldwide, despite Denmark and Sweden having included low energy building in their planning laws in the early 1980s. Grants are available for energy efficient building projects.

In Britain the government has taken a decisive step recently, declaring a ‘… a move to zero carbon homes from 2016 (and zero carbon non-domestic buildings from 2019)…’ in its Carbon Plan. Not long ago houses achieving low energy standards were the prerogative of adventurous, environmentally conscious individuals. Now two housing projects are under way, steered by the Homes and Communities Agency under the umbrella of its Carbon Challenge and in cooperation with large construction companies. Hanham Hall near Bristol will be built by Barratt Homes and South Bank Phase 1, Peterborough by Morris Homes. Another example is the South Bank Eco Village near Middlesbrough  in North Yorkshire.

On a European level the CEPHEUS project was a collaboration between several partners with the support of the European Commission. Over 240 houses were built in Germany, Austria, France, Switzerland and Sweden.

In America the Passive House Institute US lists 28 projects at present. Considering that in 2010 there were assumed to be just 13 buildings there is a long way to go but the pace seems to be increasing.

Around the world organisations like those named already or the Passive House Institute of New Zealand and the Passive House Association of Hungary are taking the concept into an increasing number of countries. In times when climate change has been accepted even by former sceptics such as Prof. Richard Muller, lessening our impact on the environment despite living in comfort has become not just a necessity but actually possible.

The old argument that environmentally friendly building is too expensive doesn’t hold true. Real costs have come down and are getting pretty close to those of conventional building methods. What is more, the price of shunning sustainable practices is far higher in the long term than any saving that might be had by sticking to the old and incrusted. A zero carbon house is not a panacea but if we want to stop the environmental rot we need to realise that what used to be utopia has become the only way out.

Another challenge is to use low energy and zero carbon technology with existing housing stock. Impossible? It has been done but cost can be the decider between renovation and demolition for subsequent new build. I will explore this further in future articles and report on the progress of some of the projects mentioned here. At least one thing is for sure, the zero carbon house is real alright.

Useful Links                        

  • IG Passivhaus – this is only in German but their knowledge base Passipedia has an English mirror site (see below)
  • Passipedia in German or in English
  • Zero Carbon Hub  - this is a public-private partnership based on the British government’s goals for low energy and zero carbon housing. The information can be a bit technical and reading like a policy pamphlet in places but it offers a lot of information
  • Zero Carbon Compendium – info on zero carbon projects and research around the world. A bit superficial but could be useful and is presumably growing
  • In Britain the Passivhaus Trust furthers the understanding and development of passive buildings
  • National Renewable Energy Laboratory – the American government’s central research organisation for renewable energy. Obviously this covers the whole spectrum but the website's search facility allows to look for articles on the zero carbon concept
  • International Passive House Association


"When I heated my home with oil, I used an average of 800 gallons a year. I have found that I can keep comfortably warm for an entire winter with slightly over half that quantity of beer."

Dave Barry


See you next week


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I liked the idea of making use of renweable resources of energy for the heat objective. This will help the non-renewable resources to maintain for years. Thanks for such an useful share.

Thank you for your comment. I am glad it has been of value. Should you be interested in articles on other aspects of low-energy housing, please let me know. I am more than happy to pick up suggestions.

I liked the idea of utilizing renweable sources of energy for the heating purpose. This will help the non-renewable sources to sustain for a long time. Thanks for such an informative share.

you are spot on. With more interest and government support the necessary knowledge, skills and materials will become available more easily. That in turn will bring prices down together with emerging competition and so on. In Germany building companies (or should I call them manufacturers?!) are offering even a wide range of 'flat pack' low-energy houses off the peg. I'll look at individual aspects more closely in future. In the meantime if you need further information or have specific questions I'll be glad to help.

Just stumbled across this article while looking for some easy-to understand introduction to the topic - thanks! Personally I find sustainable builds overpriced so hopefully in the future it will become more affordable!

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