Why and how did CAT use rammed earth and earth blocks in WISE?

The Sheppard Lecture TheatreThermal mass of the rammed earth walls

The 7.2 metre high round walls of the lecture theatre in WISE are the highest rammed earth walls in the UK. They are 500mm thick and contain approximately 320 Tonnes of earth. Due to the location of CAT, there is very little soil on site and as such the earth used for the Sheppard Theatre had to be brought in from elsewhere. The quarry used was Llynclys Quarry, near Oswestry; this was the same quarry that provided the earth for our Information Centre. The material used was a waste product that had already been processed and graded to particles of 6mm or less.

A proprietary circular shuttering system with an adjustable radius was used, and earth was added in 150mm layers and compacted using a hand-held pneumatic ram. There were four sections of wall built, with two full-height gaps for doors. The walls are structural, providing support for the roof of the lecture theatre


Why use rammed earth?

Earth is a benign material that is often a waste product in building projects, and that can easily be sourced locally, either from the site itself or from nearby quarries or other building projects. It requires relatively little processing: simply grading to particles of 6mm or less and having the correct proportion of sand to clay.

Inclusion of thermal mass is often given as a reason for incorporating rammed earth walls into a structure. This means that it can absorb high amounts of solar energy/ heat, which is then released into the building when it cools down, keeping a stable temperature. This kind of passive solar heating is a very energy efficient means of keeping a comfortable temperature in a building, but should be coupled with a favourable orientation and limited shading.

In the WISE building, the lecture theatre walls are internal only and are largely surrounded by timber framed glazing on the Southerly walls and hempcrete, so the solar energy travels through the glazing and is absorbed by the earth walls, which prevents the building from overheating and buffers the temperature at colder times of the day by releasing the captured heat slowly.

Earth BlocksEarth blocks for the ground floor internal walls

In addition to the large rammed earth walls, earth blocks have been used for the ground floor internal partition walls, which adds further thermal mass to the building. To make these earth blocks, unstabilised subsoil is compressed into a mould; these can then be laid like conventional masonry , using a thin layer of clay slurry as mortar.


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