In April 2014, 115 West Street in Sandton achieved a 4-Star Green Star SA Office As Built v1 rating – a recognition of “best practice”. It is the cherry on the cake for the building, which has received numerous awards since its completion in 2012.

Alexander Forbes signature Sandton office building, achieved 48 points for its design rating and it took roughly five months to work towards submission for the As Built rating with a final scoring of 47 points.

Obtaining Green Star SA status was a requirement from the tenant, Alexander Forbes, as they specifically wanted their office to be a sustainable building.

The building consists of eight office floors and six underground parking levels, and is conveniently situated across the road from the Gautrain’s Sandton station. Features that stand out are the zinc-clad scallops for shading, full size trees in the atrium and

Y-shape bridges suspended from the roof. The design also includes a lot of natural light, energy-efficient lighting, high-speed lifts, grey water recycling, and passive heating and cooling systems.

A contractor’s perspective

The Alexander Forbes project was a joint venture between WBHO and Tiber Bonvec Construction. Gideon van den Berg, green building coordinator at WBHO, says Alexander Forbes is their third project to achieve a Green Star SA As Built rating.

Their biggest challenge was to ensure all the correct products and materials were sourced and used by the relevant subcontractors. They then had to enforce the Green Star SA requirements without impacting production on site.

Education was a challenge. Van den Berg explains: “Many of the sub-contractors and some of our own employees had not worked on a Green Star SA rated building before Alexander Forbes as it was still relatively new in the industry. So we had to continuously make sure that we kept the relevant subcontractors up to speed with the requirements and we assisted them with implementing them.”

Site management played a big role in this, and together with the Green Star SA AP from Tiber, Nomasonto Tshehla, they were able to manage this process without affecting the project. “It is an everyday challenge,” says Tshehla, “to either work productively or sustainably as it often goes against each other from a contractor’s perspective.

The contractors for this project developed a spreadsheet with a breakdown of all Green Star SA credits, and which subcontractors would be affected by the requirements of these credits. It’s a useful tool that Tshehla now uses on other projects.

The main scoring item from the contractor’s perspective was MAN-7 Waste Management. This entailed diverting 70% of the waste generated on site from landfill. The project was completed with a total of 77% of waste being diverted from landfill, scoring the maximum three points.

From Design to Built

When one compares the Design rating process to the As Built rating process, the fundamental differences are in reporting. Peta Brom from PJ Carew Consulting and sustainability consultant on the project explains: “For a Design rating we rely on Architectural Workstage 4b documentation; the specifications and tender drawings and documentation, whereas for As Built, we have to submit As Built drawings, contractor audits and commissioning records, which are all produced after practical completion and in some instances after occupation.”

In this way, it may not even be possible to achieve an As Built rating until many months after a building has been occupied because the building services are not set to work before this.

There have been a few complications in implementing the design. In one area the low-VOC wallpaper adhesive started sliding off the substrate and an alternative non-compliant adhesive was used in order to meet performance requirements. The area where this happened was not significant enough to lose the VOC point associated with adhesives.

However, it did result in a change in reporting and in the compliant areas. Had this impacted a larger area, they would have lost a point.

Energy reduction

The project achieved two extra points for overall building energy reduction in the As Built submission. Etienne Terblanche of PJ Carew Consulting explains that the increase in the number of points claimed is due to two factors.

“For Design ratings we need to use conservative assumptions with regards to the energy consumption of the various HVAC equipment considered, whereas for the As Built submission we have access to measured consumption, which is more accurate,” he says.

A bigger impact on the awarding of the two extra energy credits was the time schedule applied to the basement extraction fans. “In commissioning, the basement fans were connected to timers and controlled to operate at lower levels when less motor vehicle traffic is expected,” says Terblanche. “This resulted in massive energy savings.”

The full feature appears in the June-July 2014 issue; page 81. Photography Christoff Hoffmann