Architects keen on low-energy can go play in the mud.
Rammed earth: Dirt is free, plentiful, and when compressed it has excellent thermal and acoustic insulation properties. Just excavate the soil, add a chemical stabilizer such as lime or sugar paste, compact the dirt between wooden formers, and "voila!" You have a durable, strong and highly insulated wall.
The build process is simple.
Selected soil is mixed to the right consistency, compacted in layers using hand tools. Forms are used to act as a mould for the wall. Other materials can be added to improve compaction, such as ground glass, shredded rubber tires or natural fibers. Once the wall has been constructed, the forms can be removed. The wall is immediately ready to take structural loads.
Rammed earth walls used as internal partitioning can also suppress noise transfer between rooms very effectively. But is the design of complex multi-layered building envelopes really more effective at temperature and energy control than a basic hut made of straw and mud?
Newcastle based architect Jane Darbyshire & David Kendall designed Europe's largest internal rammed earth wall for the Rivergreen Business Centre at Aykley Heads in Durham. The decision to create a rammed earth wall in the Aykley Heads project was by the client, Rivergreen Developments. The company had seen an earth wall at the Autonomous Environmental Information Centre (AtEIC) project at the Centre for Alternative Technology in Powys, and wanted to try the technique as part of its commitment to sustainable construction.
The downsides of using rammed earth is controlling the shrinkage of the wall, lack of national guidelines for design and construction, higher labor costs for the compacting process, and limited data on the materials' physical characteristics.
Undoubtedly rammed walls are a worthy contribution to sustainable architecture, but their use will not outweigh the energy used by conventional gas-fired heating or electrically powered ventilation. To save energy in the latter, look to engineering firms who believe in smartHVAC designs to further decrease environmental impact. Mariano Engineering has adopted low-energy-specifications as standard procedure when designing plans for architects.
Want to know more? "Rammed Earth: Design and Construction Guidelines," was published in 2006. It gives practical advice on the material selection, construction, design, detailing, maintenance and repair of rammed earth walls