Awarded a 4-Star Green Star SA rating earlier this year, 102 Rivonia Road is taking its place in Sandton’s fast-changing skyline, largely thanks to its facade. The new 98 800 metres squared building offers high-tech open office space, developed with sustainable design, building performance and occupancy experience as top priorities. The building’s design was shortlisted in the 2012 World Architecture Festival’s Future Office Category. The building consists of two towers: the Ernst & Young (EY), tower with an internal atrium, and Eris tower that both have double-glazed facade sporting an intricate pattern of vertical fins.
“It’s quite a tight building around an atrium space,” says lead architect Bob van Bebber of Boogertman & Partners. Optimal interfloor connectivity and harvesting maximum natural light without heat gain features prominently. The key architectural elements complement and connect the two towers.
The EY tower has a ground floor and seven levels while the Eris tower has 13 levels and a ground floor. “The EY tower is based on a 17-metre wing with an internal atrium,” says Van Bebber. “What we’ve done differently is its triangular form, with the corners softened with curves. A core on the western side anchors the Eris tower while the EY tower’s anchoring core is on the eastern side.” The design allows the short tower to be developed to the height of the tall tower if the need arises.
According to Van Bebber, the design’s facade “is the most significant passive sustainable design element of this building”. Both towers benefit from the same design: a double glazed facade with performance glazing from floor to ceiling, finished externally with a dense pattern of vertical aluminium fins. These vertical fins rest on 1200mm centres, and are not only an aesthetic feature.
“The fins are angled at an optimal 30 degrees from the sun to create shading for the facade,” says Van Bebber. “Ideally, the fins need to track the sun, creating as much shading as possible. But in keeping to budget, we had to find an optimal fixed angle.”
By passively placing the solid core of the Eris tower on the leading western facade, “almost 100% of the western facade is solid”. This translates into natural light for the south, north and north-east, and lowered heat gain from the eastern and western sides.
Van Bebber acknowledges their “concern about doing a straightforward glass building without any form of external shading”. By incorporating, among other design features, the vertical fins, the team “achieved 95% functional external shading without distracting from the overall glass appearance”.
Allison Groves, sustainability consultant at WSP Green by Design says the team “analysed the available options against solar performance and visual light transmission”. Cool-Lite KNT155 was selected for all exterior glass.
Cement and steel design
A concrete mix using a 35% fly ash was used, which reduced the carbon footprint dramatically considering that 90 000 metres cubed of concrete was used.
Murray & Roberts was the main contractor and operations director Tienie Neethling says: “Strength problems with this specific fly ash mixture are highly exceptional and we’ve been successfully using it for years.”
But using this form of concrete is not always straightforward. Replacing the cement with fly ash can lengthen the construction programme because the strip time is longer.
Using polished concrete for internal public walkways reduced material demands.
The atrium roof is a composite concrete and steel deck. Instead of using virgin steel for the building, “we’ve used reinforcing steel that has a 92% recycled content”, explains Groves.
Van Bebber says the extremely short construction programme “required us to think differently when it came to the construction of the atrium.”
“We’ve used a stretched fabric for the atrium ceiling that easily stretched across the large opening without the need for scaffolding,” he says.
Occupation phase sustainability
Rainwater tanks with a capacity of 84 000L recirculate water for toilet flushing. Estimated water savings for this building are calculated at 0.48 litres per metres squared per day.
As far as energy and water use is concerned, “the building has a highly integrated building monitoring system (BMS),” explains Karly Spronk, sustainability consultant for WSP Green by Design. Lighting levels, blinds, air-conditioning and water consumption are electronically monitored and controlled.
Spoormaker & Partners’ mechanical engineer Francois Schutte adds that the BMS resets all comfort set-points back to default with daily system start-up.
Schutte says they’ve implemented a decentralised variable air volume system, with a central air-cooled chiller plant serving both towers.
By placing the system’s air handling units against the building facade, natural air will be harvested for cooling when conditions are favourable.
Occupancy sensors monitor the open plan offices for energy saving purposes.
The building is rated 50% more energy-efficient than a conventional building of similar size.