EARTHSHIP HOME FOR WAIHEKE
A properly designed earthship requires no heating or cooling, provides its own power and water supply and treats its own sewage.
The early examples of the “earthship” buildings looked like they were perfect for hobbits, but times have certainly changed. Made predominantly of earth-filled tyres and other recycled materials, an earthship uses energy from the sun and thermal mass construction to naturally regulate indoor temperature. Orientated to maximise solar gain, the north side of an earthship has a glass greenhouse “airlock” that helps with temperature control, and the home treats wastewater by passing it through botanical cells, provides for food production and supports a row of photovoltaic panels.
An earthship is more than an eco-building style, it is an integrated, systems-thinking approach based on physics and biology inside a philosophy of working in harmony with natural phenomena to create a home that takes care of you. They are the brainchild of US ‘biotect’ Michael Reynolds, who has been refining earthship building technologies over 40 years. He has visited New Zealand twice in the past year and is currently designing his first New Zealand Earthship house for owners Dana Darwin and Liz Ross on Waiheke Island.
“Sustainable Autonomy for Everyone” summarises Mike Reynolds’ philosophy , as earthships support a move away from centralised infrastructure and towards independence and resilience.
Part of the earthship design philosophy is using recycled resources that are abundant everywhere on the planet. All over the world used car tyres tend to be a massive waste problem. These are the core structural element of an earthship with around 1000 needed for a three bedroom house along with other recycled materials such as glass bottles, aluminium cans, and cardboard. Earth, as well as more conventional building materials such as concrete and steel rebar are also used. Cardboard is used to line the bottom of tyres before they are packed firm with earth. “Bottle bricks” are created by cutting of the ends of glass bottles and joining them together. These are placed in within interior and exterior walls to allow portals of coloured light to shine through which makes earthships not only functional but also beautiful. Aluminium cans are used as bricks and space-fillers to reduce the amount of concrete needed.
The large thermal mass of the earth-filled tyres combined with more earth surrounding the tyre walls on three sides, creates a large thermal capacity for storing heat. Throughout the day when the air is warmer than the mass, thermal energy is absorbed into the tyre walls, when the air cools, the thermal energy is released by the tyre walls thereby providing a consistent ambient temperature throughout the year without additional heating or cooling.
The lower the heating and cooling load of the building, the less heating or cooling is required to keep the inside air at a comfortable temperature.
Earthships have been built in a wide variety of climatic conditions including damp climates like Canada’s west coast, Holland, England and Scotland. In these environments the watertight vapour barrier, good ventilation and adequate sun penetration are critical. Behind the tyre walls, an earthship is wrapped with a layer of high density rigid insulation surrounded by a plastic or rubber (EPDM) moisture barrier. Ventilation is achieved by working with natural convection flows to bring air into the back of the earthship via underground metal tubes where the cool temperature of the earth cools it, and by expelling hot air via vents in the ceiling of the greenhouse.
Pounding earth into tyres is labour intensive. However on the positive side, the earthship construction process can be largely undertaken by people who are not trained builders. Fully functional earthships are estimated by Earthship Biotecture to cost the same to build (including labour) as an average conventional house, however there are no ongoing water or electricity bills to pay.
Granting a building consent for an earthship is not something that most local authorites in NZ have any experience of and hence are cautious about. After meeting with Michael Reynolds in July Auckland Council are positive about approving the pending Waiheke Earthship building consent application. With the project’s aim to be the first 10 Homestar rated residential building in New Zealand, they would be crazy not to.
For more information on Earthships in the NZ context and the Waiheke earthship project see earthship.co.nz
Liz Ross is building New Zealand’s first certified earthship home on Waiheke Island.
Four million tyres are landfilled each year in New Zealand, so recycling them for use in an earthship building gives them another lease of life. Because the tyres are completely encased in earth they are not exposed to high temperatures, sunlight or oxidising agents which could cause them to decompose and leach or off gas. The Earthship sewage system differs from the wetlands approach in that it primarily treats the gray water inside the building and the sewage from the toilet outside of the building, both in smaller areas. Greywater is the used water after all receptacles except the toilet.All household sewage is used and reused in the interior and exterior planters, called botanical cells.