The new Sasol headquarters in Sandton provide unified premises for 17 of the company’s former buildings across Johannesburg in one dynamic sculptural groundscraper.

Proposals for the Sasol building design were obtained in a competitive bidding process after Betapoint, Sasol’s strategic advisor and tenant representative, sent out Requests for Proposal (RFP). The brief was for a building that enhances productivity and is highly flexible, allowing for a transition from a closed, sprawling office structure to a single, open-plan office space with room for growth in human resources over time.

Speaking of the concept that went into their successful RFP response, Gregory Sacks of development company Alchemy, says: “Every design idea we had was cross-checked with the brief.” In this way the design team was rigorous in ensuring that they were pitching with a strong concept that honoured the brief at every turn.

Efficiency and comfort

The desire to maximise coverage to reduce height produced a structure supporting 10 storeys of office space above seven storeys of basement parking. Due to the large volume of parking, Alison Channing and Yogesh Gooljar, environmental sustainability consultants from Paul Carew Consultants, (PJC) were asked to do an exercise in quantifying how many working hours and CO2 would be saved by installing a parking management system, which uses motion sensor lights. “The results were so surprising that the client very quickly approved a parking display management system for inclusion. It showed a saving of up to 21 600 working hours and 303 890kg of CO2 per year,” Channing says.

Once inside, convenient amenities are available, including conferencing facilities, restaurants, and fitness centre, among others. “These have been well received by employees,” says Sasol.

Natural light and passive thermal comfort were key energy strategies for the building. Access to natural light is often challenging in deep footprint buildings but the team sought to maximise the use of available light without compromising thermal comfort. PJC modelled the amount of solar radiation each part of the facade would receive and adjusted the height and position of the insulated spandrel panels accordingly.

Powerful first impression

The glass facade has undulating bands of performance vision glazing and textured spandrel that wrap the building in a wave-like motion. This, combined with the irregular building form, meant both curved and warped double-glazing as well as a facade framing system that could curve in plan and elevation were required. These requirements pushed the boundaries in the South African glazing industry, drawing on the latest technology available internationally. The facade team from Pure Consulting spent about nine months debating the details of the design and ensuring the industry was geared up for manufacture.

Pure worked closely with AGC in Belgium to develop a new glass product. The vision glazing was shipped to South Africa in non-standard oversized panes that allowed them to achieve the required heights of the vision glazing and reduce wastage. The high specification of the double silver performance vision glazing required the local producer, CnC, to upgrade their furnaces and processing machines to be able to produce the units. Geustyn and Horak, the curtain wall sub-contractor, imported equipment from Italy to manufacture the curved frames. The final product is a unitised facade system that slides into position and locks into place. It represents an amazing interdisciplinary effort.

The potential for glare into the offices from the atria also triggered deep consideration. A few design iterations were debated. Sacks says: “In the end we went with a static design for the baffles, which was much simpler, but which was also optimised in shape and position for the best results.”

The glazing alone couldn’t achieve the comfort levels required for the building’s high-performance objectives, so PJC, landscape architects Insite and Pure collectively developed a landscaping plan that optimally shaded the facade.

Bringing nature in

It was important to Sasol to support bird life, so the landscape architects incorporated the provision of bird habitats into the design of the ground floor podium. There are 4000m2 of roof garden on the podium level, which consists of four different biomes – wetland, highveld forest, highveld savannah and highveld grassland.

Consideration for the site’s urban ecology didn’t end with plant selection for habitat creation and education. The irrigation system was also designed with the highest environmental performance standards in mind. Drip irrigation was introduced at ground level. Each biome zone has different water requirements, and so the watering schedule was custom-set to each zone. As a final touch, excess irrigation water is channelled from the podium and captured for re-use, ensuring no excess water goes to waste.

Rewarding complexity

Sasol’s groundscraper is a building of considerable scale, but according to Reon Govender, contracts director of Aveng Grinaker-Lta, the biggest challenge lay in the structure’s complexity. “The perimeters of the floor plates on each of the first eight levels cantilever over the plates below. There is a large cantilevered section in the north-west corner that is 25m high, 15m long and supports four levels of offices above it. Due to program constraints, the external glass facade was installed while the concrete structure was being constructed four levels above,” Govender says. All this meant that safety had to be rigorous. “We needed to do specific designs on the safety of the formwork, which was then double-checked by the structural engineer to ensure integrity. I think the one item we are all very proud of is the fact that we had 2.5 million injury-free hours on the project, with a peak of about 2000 workers on-site.”

Sacks tips his hat to the level of detailing required to achieve the final product. “There was a concerted effort by the whole design team. Paragon in particular put in a huge amount of time and the design detailing was astounding,” he ends.

By Peta Brom

See earthworks issue 37 Apr-May 2017 for the full feature.