What is earth building?
Earth building involves various techniques for turning sub-soils into useful building materials that are bound together with clay. Clay is the smallest particle in sub-soils and when it is dry a suitable mix will binds other soil aggregates such as sand and gravel together.
Earth building methods include:
- structural walls of mud brick (adobe) or pressed earth brick, laid up into a wall with suitable mortar
- structural walls of rammed earth (pisé), where moist earth is progressively compacted into removable form work
- structural walls of cob, where a moist earth mix is progressively added in-situ to a wall and trimmed fair
- rammed earth, brick, or cob as an infill into a structural timber post and beam structure
- internal earth brick veneers (note: earth is not suitable for external veneers)
- earth plasters
- earth floors
What soils are suitable for earth building?
All soils need to be tested for suitability in accordance with how they are to be used, and NZS 4298 sets out the required tests, and many of them can be done by an owner -builder.
Isn’t earth building building relatively new in New Zealand?
No, its been done satisfactorily for over 150 years up and down the length of the country. Our oldest known earth building, Pompallier House, in Russell, stands two stories high and was built in 1841.
Isn’t earth building (traditional to the drier climates of the Middle East, North Africa and the American Southwest) unsuited to New Zealand’s wetter weather?
Earth building is not just traditional to the drier areas of the world. Britain, France, Russia, Germany and China, as well as most other countries, have successfully built with this abundant and ever present resource for hundreds of years. In Germany a standard building code for earth houses was in existence before World War II. New Zealand earth buildings up and down the length of the country have successfully withstood rain, wind, heat, freeze and thaw, and earthquakes for up to 150 years.
Don’t earth walls revert to mud when it rains heavily, especailly with NZ’s wind-driven rain?
No. There is an old English proverb of “give ‘em a good hat and boots” and this advice is still essential. Roof overhangs (a minimum of 6OOmm all round) are essential for earth buildings. NZS 4299 has proscribed roof overhangs that give the required amount of roof overhang for any given weather exposure. This, together with a good foundation that stops ground moisture getting into the bottoms of the walls, ensure that earth buildings will last for hundreds of years (Note that these comments also apply to all buildings made from conventional materials too.) Roof overhangs are also essential to control unwanted summer sun.
In New Zealand stabilisers such as cement are sometimes added to improve the strength and weathering of the earth walls. Alternatively, unstabilised earth walls can be given added weather protection by a plaster or some other kind of coating (in the same fashion that timber, fibre-cement and concrete block are given coatings to make them fully weather proof).
Must I use a stabiliser such as cement?
No. You do need to test your earth mix to show that it meets a range of various requirements such as strength and durability. Very good earthen materials can be made from a wide range of materials that are bound together with natural clay that suit a wide range of applications, and some of these can be stabilised with a variety of aggregates. There is no reason to use chemical stabilisers such as cement unless there are no other useful materials around that will meet performance targets.
What about the susceptibility of earth buildings to earthquakes?
All over New Zealand and in all seismic zones of this country, earth houses have successfully withstood earthquakes. Wellington, Nelson and Marlborough are well known for being in our country’s worst seismic zone, yet they have many examples of long-standing earth buildings. The Christchurch earthquakes showed us that that reinforced earth buildings built in accordance with the NZ Earth Building Standards survived well, just as they showed that badly designed and built buildings of steel, reinforced concrete, and timber will also suffer damage, and even be totally destroyed in severe earthquakes. It is a matter of design and construction in accordance with the properties of the various materials.
Aren’t local bodies against earth buildings?
Territorial Authorities (TA’S) are not specifically “against” any specific type of structure. If when you approach them with an unfamiliar building medium, you provide proper information about weather resistance, durability, strength and engineering calculations, they usually issue a building consent after due consideration of your submission. EBANZ knows of no case where, after following this procedure, a building consent has still been refused. The suite of three New Zealand Earth Building Standard from acceptable solutions within the NZ Building Code which mean that a building designed and built in accordance with them can not be refused consent. See also the page on the Earth Building Standards.
What does the term “natural building” mean?
In the 20th century we called earth, strawbale, and related building methods “alternative”. Now we use the term natural building. Ideally, all homes would be built from natural materials using localized appropriate building technology. Once that was the way most houses were built, and it is called the vernacular. The “alternative” to natural building these days is destruction of our planet’s life support systems, a process very largely aided and abetted by the way our buildings, and our societies, are constructed. Over-large, resource-gobbling buildings that go well beyond need have no place in an equitable world. We really do need to build smaller, and smarter with natural materials in ways that use local resources and appropriate building technologies.
Is there any special or particular way that you design an earth building that is different from say from a conventional light framed timber home?
Any design must suit the materials used. Earthen materials are generally fairly low strength so like to be used in large thick reinforced chunks that are held together at top and bottom with bond beams and continuous footings