Monaghan Farm is an eco estate to the north of Johannesburg and it’s decomposed granite soils were suitable for rammed earth. This design incorporates 500mm thick rammed earth walls,  underground rain water tanks, a roof optimised for solar shading and rainwater harvesting and off grid living.  The use of polymer stabilised foundations not only significantly reduced CO2 but also saved costs.  There is a paper I wrote on the use of polymer stabilised foundations here  

What were the specs from the client for this house? 

To design a low carbon house that had future proof resilience. It was to provide a home and a working environment that was thermally comfortable. The house was to be independent of municipal services and to be made predominantly of rammed earth. Early on it was determined to make a cement free house 

Is there anything you or your client would change?

A living roof was considered but it was determined that its footprint and cost was substantially more.

What is a rammed earth wall, and why does it need a specific soil?

A rammed earth wall is constructed by ramming earth within forms, that are then removed. The clay of the soil holds the sand and gravel particles together, and having a well graded soil assists with the structural properties of the wall. In this project we stabilised the rammed earth with a polymer bitumen mix in the below ground construction, and with lime in the above ground Walls. The stabilisation combines with the clay and makes the wall resistant to water weathering.

What other eco-building techniques/methods did you use in this project?

We used a labour intensive method in the construction which reduced the amount of fossils fuel and hence limited the release of CO2 . We provided employment for a team of around 30 people.
We also used traditional adobe bricks for the internal walls and the beam fill and rendered these with a traditional lime plaster.
We used compressed earth blocks for the internal walls and the beam fill and rendered these with a traditional lime plaster.
We limited the construction waste. Our total waste was equal to what a conventional building project will produce in a week.
We used mainly natural finishes with reclaimed timber used for much of the fittings.

What are polymer stabilised foundations

This is a tequnique pioneered on this project and comprised foundations made of rammed earth, that were stabilised with a bitumen polymer mixture. Mixing was done in a traditional cement mixer, before the material was layered into the foundation trenches and compacted

Is it off the grid?

Yes the project is both off grid and grid connected. Rain water is collected in a 140 m3 water tank below the patio and is sufficient to supply all the water needs to the house (garden included) The house has a grid tied meter and inverter and solar panels are added as budget allows.

Did you use any new techniques you hadn’t used before?

Yes, this house pioneered the polymer stabilised rammed earth foundations as well as a polymer stabilised rammed earth undersurface bed. This construction technique required that all the services be placed before any construction, so not only did the design need to be spot on, but the sub contractors were required to work in a new way. A land surveyor was employed to set out all the points with datumn levels prior to the service contractors.