Category Archives: Earthship NZ News

All of us in New Zealand have been irrevocably challenged by the events of the Christchurch Earthquake on February 22^nd.

I know a number of you have already asked the question – is this the time for Earthships in New Zealand?

Foremost we need to put the human issues first and allow people a time to process and grieve for what has happened to their City (and my hometown).  Once people are ready then we need to help them rise up and offer support to them to think about their future and what sort of house and community they would want to rebuild their ‘home’ in.

I was fortunate to be able to help out in Christchurch, working as a volunteer with the Red Cross and was able to see some of the damage first hand.  I wanted to provide a lay person’s opinion of how this event continues to mould my view of Earthships and sustainable housing in general.

[Disclaimer: None of the following is objective or remotely scientific, nor have I had the chance to sample a decent amount of the city’s architecture]

The violence of the Christchurch Earthquake was unprecedented.  The Richter Scale does not fully convey the impact of the forces at work, as this was 6.3 whereas the September quake caused less damage yet it was 7.1.

The Modified Mercalli Intensity (MMI) scale is a better measure of the intensity of the shaking.  Christchurch was an MMI X, whereas last year’s Chilean earthquake, the seventh most powerful ever recorded, had a maximum intensity of MMI IX.  The Chilean earthquake was over 5,000 times more powerful than the Christchurch one yet the shaking near the epicentre was actually worse in Christchurch.

Equally the peak ground acceleration (PGA) is another measure of how bad the shaking is in an earthquake.  According to an article in the Los Angeles Times , the maximum PGA in the Christchurch quake was one of the highest ever recorded anywhere.

I observed that the quake ‘lay lines’ throughout Christchurch were quite surgical in that some houses were relatively unscathed next to those that were completely destroyed.  I noted that some large (‘Oamaru Stone’) sandstone block homes less than 10 years old were condemned back in September due to the movement of the walls and the inability to rectify the displacement.  Certainly brick homes, and those of a more rigid construction in general, did not fair well.  Timber-framed homes broadly seemed to fall into two camps: more recently constructed ones flexed and buckled but seemed to stay together; whereas those older structures crumbled like matchsticks in the worst affected areas.

The only official Earthship constructed to date in New Zealand is the Gubb’s Earthship in the Waikato.  The construction of the rammed earth tyre walls deviated from more common practise in the Northern hemisphere by placing vertical rebar rods through the tyre walls from top to bottom as intervals of approximately 1.5m.  With New Zealand situated on the ‘Ring of Fire’, it is one of a handful of countries with stringent Seismic Survivability performance requirements.  I am sure there are countries with higher specifications but based on my experience of the Christchurch Earthquake (in an area previously not known for its seismic activity) I would think that use of vertical rebar should be adopted as standard practise in New Zealand for future Earthship construction.  This would only be possible by adopting the Gubb’s pneumatic donut-press process for ramming the earth into the tyres and use of a gantry to lower half-filled tyres into place down the rebar and then completing their pack out.

My concerns about the performance of a rammed earth tyre Earthship in a large quake would not be so much surviving as a structure during the initial shake but the displacement of the walls and the threat that would pose to the timber framed roof trusses sitting on top of them.  I am not aware of any attempts to successfully rectify the walls of an already built Earthship anywhere in the world and think this may prove unfeasible and result in Earthships being condemned as a result.  So the successful distribution of force across the wall would hopefully minimise the final displacement of the walls and hopefully avoid this issue.  To this end I would consider the use of a mesh wire fixed across the tyre walls to distribute the seismic energy as an option (the same principle used in Gabion walls).

Overall I think the sturdiness, energy performance and waste material re-use of the Earthship’s rammed earth tyre walls still make them a fantastic option for building construction.  With the modification of the construction to include vertical rebar and a wire mess finish, I think the seismic performance could be massively enhanced (speaking as one without any Architectural or Engineering qualifications mind you).

As for the rest of the Earthship design and how I think it would fair:

About 300,000 tonnes of silt was brought to the surface during the quake.  There are about 135,000 houses or dwellings in Christchurch (based on the 2006 census).  Say about half the houses in Christchurch had silt brought up either in the property or in the street outside.  That means on average 4 1/2 tonnes of silt came up for each affected house!  I’m sure that’s a conservative estimate too, as I suspect far less than half the houses in Christchurch were affected by silt.  I think the floors would have ruptured and with large amounts of floor insulation this could have been a significant problem (or maybe it would have pushed it outside of the house following the path of least resistance?).  I don’t think anyone in Christchurch truly understood the forces of nature at work before the February 22^nd quake.

Certainly the major problems facing the city after the quake have been the restoration of amenities.  With off-grid housing residents in Christchurch may not have had to worry so much about access to drinking water, power and the on site handling of sewerage.

Eight days after the quake the city of 400,000 residents had:

–         power restored to 86% of homes;

–         mains potable water (that still needed boiling) available to 60%; and

–         sewage only connected to 50% of households

Clearly Earthships with their autonomous power, potable water and on site sewage treatment would have clearly coped well.  The other great thing I’m sure of, is that the community-minded souls who want to live in Earthships would have instantly opened up their homes to their neighbours and the vulnerable in their community to ensure that no one who could be helped suffered.

[Thanks to Simon Elms for supplying the Christchurch Earthquake facts in this article]