An Aperture in the Wall A rammed earth building functions best when its surfaces are closed. Massive walls with a minimal number of openings that are as small as possible are best suited to both the nature of the material and the compressive forces that act upon it. The traditional language of earth buildings has therefore developed to take account of these properties: the walls are thick, openings are inserted sparingly – in this, rammed earth is similar to other forms of massive construction. In place of a single large window, there are multiple narrow windows, because the sections of wall in between the openings are better able to transfer the loads exerted on them. Each opening weakens the load-bearing capacity of rammed earth walls and is associated with extra planning and work and increased levels of unpredictability. Rammed earth buildings, with their simple details, have been following these principles for centuries.
The lintels in traditional earth buildings consist of timber beams
rammed into the wall itself. Loam, with an equilibrium moisture content of 6–7 per cent, is drier than wood (9 per cent). As such, wood is well preserved in earth constructions (see Materials, p. 116). Since most historical rammed earth buildings in Europe are covered in plaster, this structure is not visible. However, when rammed earth is exposed as a surface finish – which is typically the case nowadays due to its elegance and haptic appeal – the lintel detail becomes much more sophisticated. Such construction details require considerable experience in dealing with the behaviour of the material.
For smaller openings, it is the responsibility of the earth building expert
to implement the construction according to a recognized set of norms. An experienced technician can also assess the degree of reinforcement required. Here, the dimensioning of the reinforcement is based on the technician’s visual judgement; there are no building regulations or calculation criteria (see Building Regulations, p. 124). However, structural planning based on empirical data will not suffice for larger openings and the load-bearing behaviour of the lintel must be calculated. Horizontal supports made of reinforced trasslime mortar are then integrated into the construction.
The openings require a particularly high degree of planning and struc-
tural design work. Designing with rammed earth involves positioning the apertures intelligently and getting to grips with the material in the construction process. If the walls are closed, calculated erosion completes their surface finish (see Material, p. 116 and section on Calculated Erosion, p. 70). Each opening interrupts this process and creates disruption, while the earth is more liable to erosion on the drip edges on the underside of the lintels. This unintended and – if the building work is carried out incorrectly – potentially uncontrolled form of weathering can be prevented with the proper construction detailing.
Rammed earth buildings have altered their appearance: rather than
closed façades, today these buildings are also characterized by open floor plans with large, horizontal windows. But how can we design and build such openings with rammed earth? How can one do justice to this archaic, massive building material notwithstanding this modified architectural language? Or, to put it another way, how can rammed earth shed its traditional skin?
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