When I tell people we are going to build a small sustainable house their vision of what kind of house it will be varies a lot. Some think we are going to build an earth-ship or use recycled materials, others think of a high-tech zero energy home or a Cradle to Cradle home. So what is a sustainable home?
One definition of a sustainable home which is derived from the widely accepted Bruntland Commission definition of sustainable development is:
“homes that are designed to reduce the overall environmental impact during and after construction in such a way that we can meet the needs of the present without compromising the ability of future generations to meet their own needs”. 
This doesn’t say much about what kind of construction the home is or what the design principles are. Generally it is about:
- Efficiently using energy, water, land and other resources
- Protecting occupant health
- Reducing greenhouse gases, pollution, waste and environmental degradation
Different sustainability concepts focus on different areas. Below is an overview of some of the concepts that are out there, ranging from more energy focused to more organic, people, planet, profit or building process approaches. Of course there is a lot of overlap between the different strategies and a focus on materials doesn’t mean no focus on energy efficiency. All of the strategies try to achieve a better way to build homes.
1. Energy focused concepts
These concepts focus on aspects of the Trias Energetica:
- Minimize the demand for energy
- Use sustainable energy
- Use fossil energy as efficiently as possible
Net zero home
A net-zero energy home is capable of producing, at minimum, an annual output of renewable energy that is equal to the total amount of its annual consumed/purchased energy from energy utilities.
Triple carbon zero home or net zero emissions
Besides zero operational carbon emissions by the building in use, also those generated in the construction of the building and the embodied energy of the structure and zero waste at the end of its lifecycle are taken into account. There is a debate going on whether the carbon emissions of the user commuting to and from the building should also be included in the calculation. 
It is a voluntary standard for energy efficiency in a building. It results in ultra-low energy buildings that require little energy for space heating or cooling. The building must be designed to have an annual heating and cooling demand as calculated with the Passivhaus Planning Package of not more than 15 kWh/m2 .
It relies heavily on high insulation, air tightness and passive solar design. In New Zealand the Passive House Institute is the portal to go to with information on passive houses www.phinz.org.nz. 
2. Material focused concepts
A natural building involves a range of building systems and materials that place major emphasis on sustainability. This with a focus on durability and the use of minimally processed, plentiful or renewable resources, as well as those that, while recycled or salvaged, produce healthy living environments and maintain indoor air quality. Natural building tends to rely on human labor, more than technology. The materials common to many types of natural building are clay and sand. Other materials commonly used in natural building are: earth, wood, straw, rice-hulls, bamboo and stone. 
Sub concepts of natural buildings are;
- Mudbrick and cob houses
- Rammed, pressed and poured earth
- Straw bale houses
- Stone houses
- Timber frame houses
- Biobased building (using materials, chemicals and energy derived from renewable biological resources) 
For earth building there is the Earth Building Association of New Zealand www.earthbuildings.org.nz and there is an earthship website with more information and contacts. See www.earthship.co.nz.
3. People planet profit strategies
Cradle to Cradle
In the cradle to cradle (C2C) model, all materials used in industrial or commercial processes fall into one of two categories: “technical” or “biological” nutrients. Technical nutrients are strictly limited to non-toxic, non-harmful synthetic materials that have no negative effects on the natural environment; they can be used in continuous cycles as the same product without losing their integrity or quality. In this manner these materials can be used over and over again.
Summarized Cradle to Cradle follows the following principles:
- Being 100% good
- Renewably energy only
- Technical cycle and biological cycle (waste = food)
- Celebrate diversity
Living building challenge
The Living Building Challenge is an international sustainable building certification program created in 2006 by the non-profit International Living Future Institute in the US. Their mission is to encourage the creation of Living Buildings, Landscapes and Communities in countries around the world while inspiring, educating and motivating a global audience about the need for fundamental and transformative change. It is a framework that assesses homes on seven different performance areas. It is the most rigorous performance standard for sustainable buildings in the world. 
4. Building process focused concepts
Industrial, flexible and demountable building systems
Industrial, Flexible and Demountable building system (IFD) is attempting to create more adaptable buildings while managing its end-of-life more efficiently and focusing on the long term performance of structure and materials. It doesn’t focus only on the building or installations but also on the building process and organization of it. Industrial building concerns the process-related aspects of production, robotization, mechanization, automation, prefabrication, communication, etc. Flexible building involves products that are made in accordance with customer’s wishes and the possibility to make adjustments when the building is in use. Finally, demountable refers to the sustainability of the building. IFD building requires co-operation and a multidisciplinary approach during the design process 
Prefab New Zealand www.prefabnz.com is the hub for pre-built construction.
What concept to choose?
All these strategies have aspects to them I like.
For me a sustainable home is more than a home that doesn’t harm the environment or has a low energy use. It should also be a healthy and comfortable home, give a sense of place, spirit or happiness to the people living in the house, be affordable and help inhabitants achieve a good work/life balance. The Living Building Challenge is for me the framework that comes closest to what we would like to achieve with our home. Also having worked in engineering and serial production as a designer I have more affinity with the industrial, serial production of prefab and precision engineering so lean more towards these kind of building technologies and believe a lot of innovation and improvement can be achieved by improving the building processes.
More about our goals for the project and different frameworks to assess the “sustainability” of homes will be included in upcoming blogs.
If I have missed any important strategies or concepts for building houses or you think the overview is incorrect just let me know and I’ll revise this overview.