Nk’Mip Desert Cultural Centre| Copyright SIREWALL
Rammed earth is one of the oldest methods of construction, and has been used for millennia. Although some of the oldest standing walls are 6,000 years old like the Great Wall of China, still some people wonder whether this type of construction would be a viable option for today’s rapid and energy intensive construction market.
The main material in a rammed earth wall is soil, subsoil to be precise. The wall mix is principally gravel, sand, silt, clay, water and air. These materials can be gathered from the proximity of the construction site, so the embodied carbon in these types of wall tends to be very low: extraction and transportation require minimal energy if taken from a local quarry, and the energy required for the fabrication of the walls will also be very low, mainly dependent on the machinery used for compacting the earth mix. The sampling and mixing process to create the earth mix might also consume low amounts of energy, although it could be done manually. Overall, the embodied carbon of a ‘Raw Rammed Earth’ wall is very low. But, could it be built in a cold environment? Definitively.
In cool and cold climates, a raw earth wall will most likely not be enough to provide enough thermal comfort unless the wall width increases dramatically. In our climate there are two options that will perform well:
- Cladded Wall: to decrease the width of the overall assembly, the wall could be insulated and cladded from the outside (insulated rainscreen layer) to protect the rammed earth wall. In this option, the rammed earth finish will only be visible from the interior
- Sandwich Wall: to have exposed rammed earth on both interior and exterior surfaces, the wall will need to be a ‘Stabilized Rammed Earth’ wall in order to increase strength and reduce permeability. The wall will be similar to a sandwich panel, where there would be a double-wythe profile of structurally reinforced rammed earth with insulation in between both wythes or ‘layers’.
Barker Residence | Copyright Emily Blackman by Tapial Homes
The earth mixture in a stabilized rammed earth wall contains some form of cement or lime stabilizers with higher embodied energy and carbon than a raw rammed earth wall. Below are some values provided by the Inventory of Carbon and Energy (ICE) of some of the materials that will be part of a stabilized wall.
|Material||Embodied CO2e (kgCO2e/kg)|
|Raw rammed earth||0.024|
|Stabilized rammed earth (earth mix containing 6% cement and 2% lime)||0.084|
|Mineral Wood insulation||1.28|
Even considering the concrete stabilizers in the wall, the embodied CO2 equivalent is still quite low in a stabilized rammed earth wall compared to other materials used regularly in the construction industry.
The Hanson Home | Copyright AERECURA Sustainable Builders
Embodied CO2e is something we should always keep an eye on, but we should not forget the main function of a wall is to protect the interior space, and act as a:
- Water barrier
- Air barrier
- Vapour and thermal control layer
- Acoustic barrier
- Insect barrier
- Fire barrier
- Protection against vandalism
Rammed Earth Walls check all boxes while providing an incomparable finish and texture, which is what drives so many people towards this type of wall. The cost per square foot will be dependent on the amount of wall area, location of the project, project timeline, among other items. And the benefits are countless, mainly being a natural material which will not release any harmful chemicals or VOC into the living space.
The colour in the wall is customizable for any new build. To get the selected colour, the builders will use pigments mixed with the earth mix to create the different layers and accent colours within the wall. Overtime, the colour will tend to fade, though usually it is not drastically noticeable as the fading occurs gradually and homogeneously over the entirety of each facade.
To wrap up this post, durability and resilience are probably the most important and overlooked characteristics of any building. Overtime, staining and/or efflorescences might appear in an exterior wall where there is long-term water exposure. The use of roof overhangs is strongly encouraged to increase durability, not only in rammed earth buildings, but in any construction with a porous cladding material. To increase resilience of a building we should look into which elements of a building will provide a huge performance improvement in case of a drastic change in climatic conditions. For this reason, windows and window shutters should also be carefully curated for each project and location.
And with this note, we will leave this topic for the next post. Keep tuned to the TABC Blog!
By Ana Gascon