Construcion Con Superadobe

Building an earthbag dome
BY ROB WAINWRIGHT Earthbag building, also known as superadobe or flexible form rammed earth building, is a newcomer to the sustainable building scene in Australia. The technique has been developed by several architects and builders around the world; well known amongst these is Nader Khalili of Cal-Earth (California Institute of Earth Art and Architecture). Although manyload bearing straight walled structures have been successfully built with earthbags, it is in the curved form of domes and vaults that the technique really excels. The beauty of these shapes, combined with the low embodied energy of this building method and its excellent thermal performance, led us to choose earthbag as an appropriate human scale way to build. Unlike conventional rammed earthconstruction, earthbag building is well suited to sites where an ideal soil mix isn’t present, and the grunts and laughter of human labour are able to replace the roar of machinery. The basis of construction is the filling of polypropylene or hessian bags with a moist mix of soil, which is then compressed by ‘tamping’ with hand tools. Barbed wire is included between each row and has a dual purpose; tohold the bags in place while tamping, and to provide additional tensional strength in the wall. The Northern Rivers of NSW is a region with a sub tropical climate, fairly consistent rainfall of 1200–1500mm per year, warm wet summers and cool dry winters. The sustainability education centre where this earthbag dome is being built experiences temperature highs of 40°C in summer, with overnightsubzero temperatures in winter. The 4m diameter, 4m high
6 • TOB 145 • February / March 2008

structure was designed to withstand these climatic factors whilst providing a functional outdoor entertainment area and store room. It also provided us with some much-needed practice with local conditions and materials, before tackling a larger project. My wife Stephanie and I have both had former lives inthe healthcare industry; Stephanie as a naturopath and myself as a pharmacist. Unhappy with the lack of importance placed on the natural and social patterns by the economically powered mainstream culture in which we were immersed, we moved to the foothills of the Border Ranges National Park. Here we’ve spent the past two years studying permaculture, the last six months of which has involved thebuilding of the dome for our major project. Stephanie studied superadobe construction with Nader Khalili at CalEarth in May last year, while I completed an intensive workshop in Belize, Central America earlier this year with Kaki Hunter and Donald Kiffmeyer, authors of ‘Earthbag Building – The Tools, Tricks and Techniques’ (see Bookshop pg 71). This book became our bible, helping us to plan andimplement our design and we recommend this highly
Trench excavation was done with a backhoe.

practical book for anyone looking at building in earthbag. Some of the unique features integrated into the design of the dome include: a rubble trench footing containing a French drain, appropriate passive solar design, rammed earth flooring and a living roof.

Site preparation
Rubble trench and Frenchdrain A rubble trench was chosen for its proven track history, low embodied energy and tick of approval from famous architect Frank Lloyd Wright. Using 20mm aggregate, this style of footing, unlike conventional concrete, is resistant to the movement of water by capillary action due to sufficient air spaces between the gravel. Initial site levelling and excavation of the trench was achieved in a fewhours with the help of a backhoe and one very skilled operator. The trench was dug 700mm deep by 1000mm wide, and a thin layer of road base was placed and tamped at the bottom to create a consistent fall for drainage. Two lengths of polypipe were drilled at regular intervals, wrapped in silt stop plastic, and run the circumference of the trench, exiting to daylight on the downhill side of the...