Rammed earth

Building Regulations

From an Irish perspective the most contentious issue is actually our Building Regulations as there is no standard for building with earth. Securing finance and insurance are two other major hurdles so small scale low cost projects, exempt from the regulations, may be a good place to start.

Like cob, rammed earth has thermal mass, which means it is excellent at retaining heat and then slowly releasing it, but it provides very little insulation and the Building Regulations require a lot of it.

You would have to make the wall extremely, (impracticably so), thick to get it to comply with the Regs so insulation will need to be added, preferably in the form of earth-fibre panels/blocks as they can be incorporated in a cavity wall type of construction. Other options exist, including straw on the inside facing, plastered over with lime, and a timber formwork filled with cellulose; even external walls have been clad with insulation for Building Control purposes in the UK.

Rammed earth has similar strength to concrete blocks so there is no reason it can’t be incorporated in a new build. It provides tremendous strength in compression but none to speak of in tension, especially when damp, which is why the walls tend to be very thick, from 300 mm up to half a metre. The more compacted the earth is, the denser and therefore stronger it becomes.

In fact strength isn’t an issue for low rise earthen structures (three storeys or less) but an engineer or a practitioner experienced in earthen construction materials should be brought on board to determine the right mix and oversee the building process. In order to comply with the building regulations the mix may need to be ‘engineered’ to achieve the required performance, i.e. an additive such as lime may be added.

A way to circumvent the Building Regulations altogether is to build a timber frame and for building control purposes, use rammed earth as a decorative finish. Insulation and other components, e.g. as required for acoustics, can then be added as they would on a traditional build, as long as the materials used are breathable. This option may feel like it defeats the purpose of building an earthen house but many cob buildings actually avail of it too, despite cob walls being more than able to bear structural loads.

Prefabrication

Prefabricated rammed earth solutions exist, either in the form of precast components made off site or building methods incorporating insulation in the structure. A more recent development is the possibility of buying rammed earth wall sections and thermal mass stoves. Rammed earth turnkey companies for entire houses have also appeared, such as Sirewall or Ramtec but they offer a material which is engineered (usually bound with cement).

The eco credentials of shipping a prefabricated rammed earth house, or indeed any earth building components, to Ireland are dubious and arguably defeat the purpose of building with locally sourced materials! Indeed, in Ireland there is very little evidence of rammed earth building, which is probably due to the type of soil we have here. Expertise in this area is therefore rare but it can be obtained from the UK, where courses are regularly run, and in other parts of Europe as this building method is gaining in popularity.

Additional information: Building with Earth in Scotland by the Scottish Executive Central Research Unit (2001), Pete Walker of Bath University (UK).