The House that Susan Built
What makes a house green? Is it the energy saving features? Is it the high thermal properties of the building walls? Or is it the relentless pursuit of a journey to create a home that makes as little impact on its environment as is humanly possible?
This is the question Susan and Jakkie Botha of Jeffrey’s Bay set out to answer when they decided to build a sustainable house for their mother. Susan and Jakkie set out to prove they could build a green home using local, natural materials and could keep the cost within their limited budget.
Susan and Jakkie run a successful, edible landscape business in the Jeffrey’s Bay and Port Elizabeth area called Urban Harvest. By their own admission, they confess they knew nothing about construction and its management, so their first step was to embark on a fact-finding mission to determine which of the natural building styles would best suit their requirements.
After much consideration, sandbags were selected as the most suitable natural material to use for the construction of the house. The bags chosen to hold the sand are made of a robust geotextile material and they were readily available from the local market. The structure utilised approximately 20,000 of these specialised bags. The sand was sourced from a nearby quarry and delivered to site by the truck load. Each of the bags holds approximately 7.5kg.
The foundation was made using a crushed stone sub-base topped with sandbags. It was recommended the sandbags be filled with 1:10 cement to sand ratio for improved strength. The structural wood & galvanized sheet latticework forming the outside walls, sits directly onto the sandbag foundation. Questioning the structural integrity of sand bag walls, Susan and Jackie first carried out a field test, which demonstrated clearly that sufficient structural integrity was derived from the sheer weight of thousands of sandbags.
Although professionals were required at certain stages to fine-tune the design and the construction process, it was quite surprising and on some level, liberating to learn how the Botha sisters made use of resources available to them to achieve the majority of the build by themselves. They made use of a free version of Sketchup to draw up a 3D model of their plan and received useful tips from friends such as how to use a clear, water filled hosepipe to work out their levels.
Knowing their limitations and understanding the need to quickly learn the construction ‘tricks of the trade’, the best thing Susan and Jakkie did was experiment, experiment and experiment some more. When they bought the plot, they spent 12 months researching and closely studying the local weather patterns. Weather patterns are an essential observation for proper orientation and design of a passive house. Most importantly, the sisters listened carefully to and aimed to meet their client’s requirements.
The Botha sisters were surprised to find that they were not the first to attempt such a feat. A short time searching the Internet yielded many examples of people who have succeeded in building their own house from natural materials, right here in South Africa. This was a very important find for them as a precedent had already been established and allowed them to approach local authorities with built examples that helped to explain their own application. The local building authorities’ requirements had to be taken into account as the utilities connections would have an effect on the buildings eventual orientation.
The building process itself was a series of highs and lows. It was a very steep learning curve for the sisters, involving continuous experimentation with different materials of various recipes. For example, the ideal solution for the exterior walls was a wire mesh fixed to the sandbags, plastered with a cob mixture and sealed with lime/prickly pear juice mixture. This recipe was perfected after considerable experimentation. The building walls took approximately 1 month to erect, with an average of 5 people working per day. Sitting inside, one can appreciate the impressive thermal quality of the building envelope, even when gale force winds were battering the other side of the walls.
There was obviously a lot of preparation work to be done before building could begin, as the sandbags needed to be filled by hand. This is when delegation of priorities set in and team-work became an integral part of this project.
As soon as word spread that the building had commenced, many people expressed a desire to be part of this exciting project. People from as far as Cape Town came to J-Bay to volunteer their services and expertise. This was truly becoming a community project. Susan and Jakkie were also able to raise much needed funds with practical courses during the construction process.
In addition to the ‘natural’ building materials used for the building envelope, a solar water heater has been installed on the north facing part of the roof. The intention is to add further efficiency features such as a 50,000 litre, ferro-cement water tank for rainwater harvesting and a photovoltaic installation. A black water digester was considered, but the volume created would be too low for the system to function effectively. A composting black water system is currently being researched. It is worth noting that the roofing material was also selected on the basis of tests undertaken by manufacturers to show the effect their materials would have on rainwater collection. Some roofing materials could not guarantee that the water harvested would be suitable for residential consumption making them unsuitable.
The one factor remaining to consider is costing. What did this building cost and how does it compare to a conventional building? According to Susan, the 160m² cost approximately R450,000, which works out to approximately R2812/m². The Kitchen still needs to be accounted for, pushing the final per meter price to approximately R3500. There was a higher than usual man hours invested into the construction of this natural house. That translated into a higher total labour cost. However, there were many man hours invested but not considered in the costing as they were invested by volunteers who bartered those hours for experience. Furthermore, many of the building materials could not be considered in the per meter price as those materials were sourced at no cost. For example, the prickly pear is considered invasive and farmers were all too happy for them to be removed from their farm. The stones for the sub-base were also sourced from the adjacent properties at no cost. Another unexpected cost, considered in the final cost estimate was material loss due to theft. Susan estimates R50,000 was lost due to theft of materials and the subsequent security costs incurred with trying to minimize such loss levels.
Through trial and tribulation, Susan and Jakkie have created a truly natural house that does not negatively affect its environment and aims to be as energy and resource efficient as possible. It will be very interesting to see how the house settles into its environment and how it evolves to become even more efficient with the addition of various technologies. The lessons learnt from this trailblazing construction will no doubt be employed in other natural buildings throughout South Africa, aiding the spread of energy efficiency in a country with limited and overstretched resources.
By: Khaled El-Jabi