Monday, 16 August 2010
For some time now I’ve been studying the use of ‘rammed earth’ construction. Rammed earth is based on the compaction of graded soils into formwork to produce an unfired environmentally friendly building material. Rammed earth materials can be also sourced and produced locally, negating the haulage and storage impacts of kiln-fired masonry components and mortars.
Walls produced using rammed earth contain less than one twentieth of the embodied energy of traditional cavity walls. They are more easily returned to the ground when no longer required so the material is borrowed, not stolen. Earth walls have a high thermal mass and act as a heat sink, absorbing heat energy through the day and releasing it into the building as temperatures fall at night. Experiments have shown that rammed earth can actually reduce warm daytime temperatures by 4 or 5 degrees C - equivalent to some cooling systems. At the same time earth buildings stay warmer in cold climates, with internal temperatures unlikely to fall below 140C when occasional external sub-zeros are experienced. Given that half the energy generated in Britain is used to heat or cool buildings, the potential to reduce energy consumption makes earthen buildings an important environmental initiative.
Earth walls control humidity levels within buildings by absorbing excess water vapour and releasing it back when the environment is drier. They also have good sound absorption properties and absorb volatile organic chemicals from the atmosphere, potentially eliminating sick building syndrome. In addition to the normal applications, rammed earth can also be useful in disaster areas as it can be rapidly built using indigenous materials and local labour that requires little training.
Earthen architecture is gaining strength in many parts of the world, including Europe, Australasia and the Americas while building codes for the material are also now being developed, including new seismic design regulations in New Zealand.
Rammed earth is a material that minimises energy input in the construction phase, makes an input into energy consumption and can be returned to the ground when no longer required. It is a material with a viable future and one that won’t (ahem) cost the earth.
Malcolm Richards is a Director of Structures at Capita Symonds.