PART 2: CONCRETE IN THE DESIGN OF A UNIQUE LUXURY HOME IN GEORGE, SOUTH AFRICA

By Eamonn Ryan

In an exclusive interview, Justin Bien of OneRoom Design Architects shared insights with Concrete Trends into the design and construction of a unique luxury home in George, South Africa. The discussion revolved around the substantial use of concrete in the foundation and structure of this extraordinary family residence. This is Part 2 of a two-part series.

…continued from Part 1.

Triple P, the main contractor, managed the excavation process, which involved removing approximately 6 000m³ of sand. To prevent the sand from collapsing into the excavated area, they used natural sandbag barriers and posts. This method ensured the stability of the site during the construction of the basement and foundation.

An astonishing 11km of conduit was cast into the concrete slabs to support the smart home systems. This integration posed significant challenges, as any issues with the conduit would require intricate troubleshooting and cable pulling by electricians. Despite these challenges, the team ensured that the conduit was properly installed, with draw cables included to facilitate future maintenance.

After casting the basement and other concrete structures, the team backfilled the excavated areas to secure the foundation. Special aluminum shutters were used to cast the concrete, which were then removed and the space around the basement was backfilled. This process was carefully managed to maintain the integrity of the structure and prevent any future ground instability.

The total value of the structural work completed so far amounts to USD1.2 million. This figure encompasses not just the concrete superstructure but also additional elements such as a borehole, underfloor heating, mechanical ventilation and stormwater tanks. However, it does not include the finishes or the full mechanical systems. Had the project been completed as initially envisioned, with top-notch finishes and furnishings, the total cost could have reached up to USD4.2 million.

Structural design and steel requirements

The extensive use of concrete required 240 tons of steel reinforcement. The engineering team sought to minimise the number of interior columns to maintain an open-plan design. This approach necessitated significant structural innovation, including a 4.5m cantilever over the entranceway, which required careful tension management and support from structural walls.

The concrete used in the project was ordered to specific standards from suppliers such as AfriSam and Lafarge, ensuring the required slump and MPA ratings were met. For example, the screed within the house was specified at 35 MPA to support a terrazzo floor, significantly higher than the standard 15 MPA. This high specification ensures durability and longevity, essential for the luxurious finishes planned for the home.

Bien emphasised the critical role of the structural engineer in preventing failures. Engineers are responsible for ensuring that all structural elements met the required specifications, conducting regular site visits to check rebar placement and concrete quality. Any deviations, such as insufficient steel reinforcement or incorrect concrete curing times, can lead to catastrophic failures.

Despite meticulous planning, on-site challenges can still arise. For instance, improper shuttering during concrete pouring can lead to collapses. Such incidents highlight the importance of thorough site supervision and adherence to engineering guidelines to ensure safety and structural integrity.

The construction of this luxury home is a testament to the meticulous planning and expertise required in high-end residential projects. From extensive use of high-grade concrete and steel to sophisticated smart home systems, every element of this project has been carefully designed and executed. The collaboration between architects, engineers and contractors ensures that the final structure not only meets aesthetic and functional goals but also stands the test of time through robust structural integrity.