Portfolio | Compressed Earth Brick house (CEB) reimagines tiny RDP house footprint

by

At 42m2 this house in Scarborough uses natural building materials to showcase the potential of earth building on the scale of a standard RDP house.

In the previous post, we shared the story of three beautiful mud brick rondawels built by one of our natural building course students in Scarborough after buying a property built by Peter McIntosh. In this post, we share the story of the original earth home built with compressed earth bricks [CEBs] in 2012. The unique design is built on the same footprint of an RDP house and showcases the potential and performance of earth building.

From RDP matchbox to sustainable design

RDP is shorthand for Reconstruction and Development Programme—a socio-economic policy to provide housing and sanitation for disadvantaged communities. It was initiated by South Africa’s first democratic government led by former president Nelson Mandela, and the houses are built out of cement brick walls with concrete roof tiles or corrugated roof iron. The homes are not insulated and get baking-hot in summer and freezing cold in winter. They range between 30–45m² in size, and generally comprise an open kitchen, sitting area, and bedrooms with a toilet.

Internationally, the tiny house movement adopts similar design parameters by keeping their building footprint under +-46m². However, that’s one of the only things that RDP houses and the tiny house movement have in common. The movement’s popularity-gains is the result of more and more people adopting a minimalist approach, and downscaling in the face of economic disruption. 

Enter Kent house, completed in 2012 by builder Peter McIntosh under the auspices of Cobco, his company at the time. It was designed by architect Brian Kent to reimagine the RDP footprint through clever design and level changes, making the 42m²  feel much more spacious. A composting toilet is cleverly designed to fit into a space for which there was much competition.

Facing North, the sustainable design combines passive solar design, compressed earth brick [CEB] walls, a clerestory window, and overhangs that limit summer sun but allow winter sun penetration. The earth walls provide thermal mass to moderate the internal temperature with a central fireplace to contribute warmth during winter.

Sustainable materials

Social 

CEBs require minimal skill but some specialised equipment to compress the earth into bricks and require several workers to operate the machinery. This allows for workers with low-skill levels to participate, which creates jobs and benefits the local economy. 

In conventional buildings, most of the costs are for materials while low-skilled labour form a smaller percentage of the overall costs. Moreover, a lot of the materials are externalised as materials are manufactured off-site and prefabricated in factories. 

In natural building the goal is usually to use low-cost materials that are directly available on site, but the labour is more extensive. And because natural homes are often built by the owners over a long period in-between doing other work to earn a living, the financial outlay might seem lower. If one were to pay for someone else to do the work, the ratio between labour and material cost would be the inverse of conventional buildings. 

Environmental

CEBs require less cement and don’t require firing, which reduces carbon emissions and energy input. They are more energy efficient than conventional building materials during the construction phase as well as the duration of the building’s life cycle. 

Compressed earth bricks have a high thermal mass that helps to naturally regulate indoor and outdoor temperatures. As a result, buildings are warmer in winter and cooler in summer, which result in energy savings during the lifecycle of the building. The indoor temperatures are more temperate and the humidity levels are kept consistently stable.

Ecological

CEBs are also particularly beneficial and appropriate where the clay content of the local earth is too expansive to build with mud bricks. In other words, if a soil type is not appropriate for building with cob or mud bricks, then CEBs might be suitable because they require less water and instead rely on compression to bind the earth.

For the Kent house:

  • The sand from the site was stabilised with 5% cement and rammed back into the foundation to create a stable base. 
  • This was followed by a foundation and stem wall built with rocks sourced from a site in Kalk Bay and a mortar mix of clay and sand mix stabilised with 15–20% lime. 
  • The walls are built from compressed earth brick (CEBs) with clay from a dam near Spier and sand; and the mortar is the same mix stabilised with 5% cement.  
  • Because the bricks were already smooth, there was only one plaster coat with the addition of 5% lime in the final plaster.
  • The house also features reclaimed teak windows from a 1930s house that was demolished, and the clerestory windows were made on site. 
  • Laminated beams for the curved roof truss were made locally with non-toxic glue with untreated gum poles for the roof.
  • A large trunk from a tree cut down the road holds up the curved truss in the centre.
  • A minimum of cement was used except for long-spanning lintels to ensure there wasn’t going to be any cracking
  • River red gum from an alien-clearing project was used for the floors, and the lounge floor is clay-tiles hand-made by a local artisan.

Thermal performance

RDP houses are typically constructed from hollow blocks, which adds insulation value, but what sets Kent house apart is the dense earthen walls that add high thermal mass. 

Thermal mass refers to the rate of heat transfer through a building and leads to the regulation of internal temperature and humidity. In short, the walls absorb heat during the day and release it when the temperature drops during the night.

With the thickness of the walls of Kent house it takes approximately 7 hours for the heat to reach the interior which coincides with the onset of evening when exterior temperatures begin to drop and the process is reversed. The clerestory window also helps to release any excess heat out through the top of the building.

New beginnings

Kent house was purchased by James Kuiper after completing our CPD-accredited natural building course in 2018. Since then, he’s built a trio of thatched rondawels on a similarly small scale to create a sanctuary of living buildings. 

– Written by Tarien Roux

ARCHIVES

Copyright

Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to this blog’s author and/or owner and the Natural Building Collective with appropriate and specific direction to the original content.

Sign up

Stay informed of our course dates and other news
* = required field

powered by MailChimp!

Connect with us on social media

0 Comments