Natural building using straw/clay
Using natural materials such as earth, straw and wood is a popular topic. An information evening at school attracted about 30 people. We were exploring the possibility of using these natural materials to build the new school. Ellen Appleton was our Chair for the evening and she introduced our presenters, Steve Richards, Richard Walker, Gabrielle Bell and Peter Garlick.
Steve Richards, café owner and experimental builder, has built several earth and clay/straw buildings, including Jester House café. Steve explained his preference for the straw/clay method. The main advantages are its light weight, good insulation, easy to work with and quick building. He took us through the process with pictures from one of his projects. He explained the advantage of being able to get the roof up first then having a sheltered space to work. Standard piles and wood floors are an option due to the lightweight materials. Steve will lead us in a small hands-on project on the school farm later this year.
Richard Walker is a civil engineer and contributed to the NZ Earth Building standards. Richard has built two earth houses and engineered many others. Unfortunately the straw/clay method is not in the standards yet, so it is still an alternative solution which makes it more difficult and costly to obtain Building Consent. He explained the risk matrix that is used during the Building Consent process and the challenges that presented to earth buildings. Richard suggested an option where natural earth building methods could be mixed with conventional materials and methods to overcome some problems. Straw/clay weighs about 900 Kg/m3 whereas rammed earth is 5-6 times more heavy. Heavy earth walls require bigger foundations and more reinforcing to resist earthquake forces. Richard recommended a book Light straw/clay Construction by Lydia Doleman.
Gabrielle Bell from Bell Stephenson Architects, spoke about the school design process so far. Much of the concept design was done with the school community by consensus design in February 2015. Architect Matthew ter Borg lead that process and the results were used to gain resource consent. We are now at the preliminary design stage which is a step toward Building Consents. Preliminary design is where we must decide on materials and construction method. Gabrielle gave the pros and cons of using straw/clay as a building material, including the advantage of community input and the material is a carbon sink.
Peter Garlick from the 20/20 Vision Project Group gave a rundown of the Group’s activities. The group works in three main areas; project management, funding, and risk management. Some recent projects have been;
• A quantity survey based on concept designs has costed the school build at $4 million, plus an extra $1 million for kindergarten, play group and sports fields.
• Design and costing of roading, earthworks and car parking. This work can proceed as soon as the ground is dryer and funds available.
• Engaging architects for preliminary design work.
• Refining the funding model. The model involves state integration, donations and a major loan raising campaign.
Risk management looks at all the risks to the project and how they can be managed. One option being considered is having classrooms built off site and delivered. This would allow both the cost and delivery date to be determined. The clay/straw method could be used for the largest building which has the library/meeting room and administration. This building is less time critical as the school could move onsite before it was completed.
Group discussions considered topics such as use of community labour and skills, the differences between concrete floors, timber floors and rammed earth floors, heating and ventilation options, and how to raise the funds.
The new farm school project is a community project and relies on everyone helping in what ever capacity they can. Fundraising is also a community responsibility. The 20/20 Vision Project Group are driving the project for the community and want a two-way flow of ideas and information. Watch for updates in the weekly school newsletter and receive more detailed reports via the 20/20 group email list. Feel free to contact Peter Garlick, Mike Copeland, Ellen Appleton, Graeme Stradling or Ian Kircher.