Chapter 8 Rammed earth

Part of the walls of the home are stabilised rammed earth. This is a mix of gravel and sand with around 10% cement to act as a binder. The walls are 300 mm thick and consist of around 32 m³ of material, providing a high thermal mass. The rammed earth is structural; it supports the roof structure. However, rammed earth is a very poor insulator (\(\lambda=1.25 W/mK\)). To redress this we put an external stud wall (offset by 30 mm from the rammed earth) and used 80mm of Kingspan Kooltherm (a phenolic foam with a very high thermal resistance) to insulate the wall. In addition, the wall sits on 50 mm of high compression extruded polystyrene (XPS) to thermally decouple the wall from the footings and ground. In this way the intention is that the rammed earth can absorb and retain heat within the building thermal envelope.

Figure 20: Rammed earth