The visionary Oxford Parks development in Rosebank, Johannesburg, has seen its first building completed by Concor Buildings for the new head office of BPSA, one of the country’s largest oil companies. Significantly, the building has achieved a 4 Star Green Rating in terms of the GBCSA standards.
According to Chris Maritz, contract manager at Concor Buildings, the building is part of Phase 1 of the Oxford Parks vision, which will include three more office blocks and a hotel. Work began in August 2017 for client Intaprop, and BPSA staff relocated to the new space in December 2018. The tight schedule of less than 16 months meant careful planning, implementation and monitoring, with 300 to 350 employees and contractors on site at the project’s peak.
“This is the first building in a large mixed-use development that will roll out a substantial part of the residential area between Jellicoe Avenue and Bompas Road in Rosebank,” says Maritz. “The construction of this first part of Phase 1 comprises three basement levels of about 28,000 m2 and six office levels with a gross leasable area (GLA) of 8,100 m2, as well as 960 m2 of retail space on the ground floor.”
Concor Buildings was required by the client to take the building to tenant fit-out stage, and delivered complete office floors except for loose furniture and IT equipment. The handover of floors – as they were completed – began in October 2018.
The attractive wedge-shape design is notable for its stunning glass facades, created with 4,500 m2 of glazing. This design enhances the wellbeing of the building’s users allowing ample fresh air, particularly unimpeded access to external vistas looking east over Johannesburg’s treed suburbs and plenty of natural daylight.
To deal with the sun’s heat through the glazing without overloading the air conditioning system, a couple of innovations have been included. The first is a double-ventilation façade on the front of the building, involving two layers of glazing some 40 centimetres apart. The outside layer is open at the bottom and at the top, allowing air to rise and exit this vertical channel as it heats, sucking in cooler air at the bottom and keeping the building cool.
The second innovation is the installation of automated horizontal blinds which are linked to a weather station. Guided by the season and time of day, the angle of the blinds controls the entry of direct light into building, further promoting energy efficiency.
The main structure of the building – which consumed about 17,000 m3 of concrete reinforced by 2,100 tonnes of reinforcing – was complete by the end of April 2018.
Concrete for the slabs was pumped to the required locations, while vertical elements like columns and lift shafts were poured by bucket from a crane; from first pour to completion of the concrete works was just seven months.
Wet trades such as brickwork and plastering were mostly completed by the end of May, with some 780,000 bricks laid by the end of the project. Finishing trades were underway by June, followed by services installation on all the floors.
Being located directly above and near the Gautrain tunnel posed particular challenges for the design of foundations for the building’s basement.
“Foundations were not conventional piling and pile caps but were raft foundations due to the restriction zones working above the Gautrain tunnel,” says Maritz.
Adding to this complication were the highly collapsible soils which, in the case of rain, could have fallen into the foundation trenches. Given the large amount of steel reinforcing required in the raft foundations, the recovery of collapsed trenches could have become costly and time-consuming.
“Excavations started in August 2017, but we mitigated the rainfall risk by fast tracking this phase and we were able to complete the foundations almost a month ahead of schedule, before any heavy rains arrived,” he says.
Being a residential area, there was also a restriction on working hours due to noise, meaning that work had to stop every day by 18h00 and on Saturdays by 14h00. No work was permitted on Sundays.
“This made it necessary, for instance, to conduct our large concrete pours promptly in the morning, so that there was time to complete the slab before the end of the working day and limit the noise to floating activities,” he says.
Maritz emphasises that good planning, time sensitivity and efficiency were all the order of the day in keeping the project’s timeline on track. This included installing the glass facades in good time as several tasks, like finishing trades, could only be finalised when the building was fully enclosed.