light earth method (LEM)

The light earth technique was gradually developed since the 1980's in Europe (primarily Germany) to meet a growing demand for better insulation. It's roots are in the centuries old tradition of half-timber construction. In light earth building, loam is mixed with woodchips, pumice or other air pocket forming aggregates to create light, insulating walls within a structural wooden frame. Compared to other earthbuilding methods LEM is far less labour intensive, faster and a lot more forgiving since it isn't structural. This makes it very suitable for owner-builders. At a density between 350 and 1200 kg/cubic meter, LEM walls are much lighter than mudbrick or rammed earth walls (2000-2200 kg/cubic meter). As a result the insulation (r-value) is up to ten times higher for the same wall thickness and New Zealand building code requirements can easily be met.
External light earth walls are best complemented with the higher density of rammed earth, used as thermal mass to store heat in interior walls and floors, but also built into a load-supporting wooden frame.
This saves reliance on non-compatible reinforcing materials like steel and cement, that consume a lot of energy in production and transport, and ensures superior earthquake performance and full breathability.
The wooden frame also provides support for a protective roof, a key factor in making the cement-free earth building process viable in New Zealand weather conditions.
Our homes combine refined contemporary architecture with traditional materials and craftsmanship of the highest quality. We have set new standards in environmentally friendly building in NZ, and we are sure you will feel and appreciate the difference.

light earth method - the process

nzeb design ltd. usually works with a light earth infill consisting of pumice and/or wood chips and selected loams.
This material combinations was very successfully used on many of our projects
and produced appealing, stable walls with excellent thermal properties.
The quarried race pumice has an aggregate size varying from 8 to 55mm.
The wood chips are bark free, untreated, shredded waste wood and /or macrocarpa wood shavings and sawdust.
Suitable loam can often be found on site or close proximity. A clay content of about 30% is ideal for the light earth method. The clay merely acts as an adhesive to hold the airpocket-forming aggregates together. The loam is soaked and agitated before mixing it at a ratio of approx. 20% loam to 80% pumice or wood chips in a mixer. The mix is then poured into a temporary shuttering system between the upright members of the frame (posts or studs). The mix is lightly tempered by hand and lateral support is provided by horizontal laths at regular intervals. When dry the walls will have a density of approx. 450-850 kg/cubicmetre, which together with the internal and external plasters will produce an r-value of approx. 1.2 sqm*K/W for the 200mm wall thickness. Temperature monitoring of our project in Mangawhai over the 2004 winter period has confirmed the good thermal properties. The inside room temperature of the unheated and uninhabited building never dropped below 14 degrees celsius.

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