14 February 2011 - Aurecon’s sustainability credentials were further endorsed when Nedbank Ridgeside in KwaZulu-Natal (KZN) achieved a Four (4) Star Certified Rating, thereby becoming the second office development in South Africa to be fully certified, and the first in KZN.
Acting as structural, civil and wet services engineer on the building, Aurecon partnered with client, Zenprop, and tenant Nedbank together with WSP GREEN by DESIGN as the Green Star Accredited professional and sustainability consultant to deliver this highly collaborative project.
Completed in December 2010, the Nedbank Ridgeside Office Block is approximately 6,500 m², consisting of a four-storey office block and a three-level super basement. Hailed as the building which “sets the standard for all future development of the Ridgeside precinct”, the project was unusual in the degree of collaboration it required from the professional team.
“In order to ensure that all role-players were aware of the common goals surrounding the achievement of a Green Star rating, the team met regularly for a series of design and report-back meetings,” comments Aurecon engineer Pieter Becker.
He adds that the strict requirements of the Green Star rating system forced the professional team to challenge tried and tested building practices to come up with innovative ways of achieving the sustainability targets.
The Green Building Council of South Africa’s (GBCSA) mission is to promote, encourage and facilitate green building in the South African property and construction industries. As a silver founding member of the GBCSA, Aurecon’s sponsorship of the council’s efforts confirms its support of this mission and affirms its commitment to playing a leading role in promoting environmentally sustainable development.
Since fulfilling the role of mechanical engineer on South Africa’s first GBCSA Green Star certified building – Phase II of Nedbank’s head office in Sandton – Aurecon has gained valuable experience on a variety of sustainable building projects in South Africa.
Overcoming structural engineering challenges
The production of cement is very energy intensive. From a structural materials perspective, Aurecon Engineer Jaco de Villiers was tasked with ensuring the total amount of Portland cement utilised was kept to a minimum.
“The Green Star criteria promotes the reduction in the quantity of Portland Cement by means of either substitution with industrial waste products, or by specifying oversized aggregate which drives down the water demand and reduces the amount of cement required for a specific water-cement ratio,” explains de Villiers.
He goes on to say: “Unfortunately, the second method would increase the risk of honeycombing and would have impaired concrete compaction, which is dangerous in tall buildings. What followed was a series of complicated calculations to ensure we could utilise the first method in order to obtain maximum Green Star points. What we eventually recommended was the addition of both clinker and slag or fly ash to drive down the use of Portland cement and still meet the required strength ratio.”
In addition to reducing the amount of Portland cement, De Villiers was also tasked with ensuring the amount of structural or reinforcing steel used in the structure had a post-consumer content greater than the minimum target of 60%.
“By utilising CISCO reinforcing steel, which is 98% recycled, we ensured a total of 96% of the total amount of all steel on the project was recycled,” he comments.
Overcoming wet services challenges
Aurecon provided all of the wet services for the project, including rainwater drainage, achieving 100% of the available points under the “Water” credit. This was achieved through innovative wet services techniques such as rainwater harvesting from the entire roof area.
In addition, a system to collect stormwater was designed to channel run-off from all hard surfaces into a water retention facility. The harvested rainwater is treated and reused for flushing toilets, irrigation and heat rejection by the cooling towers.
Civil engineering challenges – stormwater design
The site is located on deep Berea red sands which are both highly erodible and very difficult to work with when wet due to the high clay content.
A detailed stormwater management plan, covering the site and associated platform areas for offices and materials, was implemented to control and attenuate stormwater during the construction phase. This included bank protection, channels and temporary attenuation ponds.
The temporary works also had to cater for stormwater conditions applicable to three distinct stages of construction: completion of earthworks, interim construction of building and the final stormwater system.
Another significant challenge included combining the full site development stormwater attenuation facility, water re-use storage requirements, a water feature and the necessary pumping equipment into a single aesthetically appealing facility that complimented the architectural design of the building. This required the use of a pond lining, gabion walls and landscaping.
In designing the services, there was extensive co-ordination required between the team members to ensure services were installed in the correct positions to service future tie-ins, not obstruct piles and other footings and connect to bulk municipal services being designed by others.
What scored the points?
Category for category, the professional team collaborated to ensure stringent Green Star sustainability criteria were met in each of the seven categories:
Indoor environment quality
- Fresh air is provided at a rate of 12.5l/s/person which equates to a 150% improvement on SANS 10400-O (5 litres/second/person for offices). Carbon dioxide sensors have been
- integrated in the return air path on each floor. This will ensure continuous monitoring and adjustments of fresh air into the building.
- Glare from natural daylight is reduced by means of a combination of fixed external shading devices and internal manual blinds.
- 60% of the office areas have a direct line of sight to the outdoors.
- Ambient sound levels and noise from the building services do not exceed 45 dbA.
- Volatile organic compound levels of office interior wall paints, carpets, adhesives and sealants are below maximum limits set by Green Star SA Office v1.
- Tenant exhaust risers have been installed to provide dedicated extraction of indoor pollutants form printing and copying areas.
- The building is a non-smoking building.
- A centralised plant provides chilled water to Fan Coil units throughout the office Space, saving considerable energy on cooling costs.
- The number of parking spaces does not exceed minimum local requirements of 1 bay per 100 m².
- 5% of the parking bays are dedicated to alternative fuel and hybrid vehicles; with 5% dedicated to motorbikes, mopeds and scooters; all with preferred parking locations.
- Bicycle storage, showers and lockers are provided for.
- Mass transport options for building occupants include minibus taxis and the eThekwini Municipal Bus service.
- Water efficient sanitary fixtures and fittings, resulting in significant water savings.
- Potable water consumption for landscape irrigation and heat rejection is reduced by 90% through water reuse.
- Water meters are installed for all major water uses and connected to a Water Meter Monitoring System to support proper facility management of water consumption.
- Use of water-wise planting for landscaping.
- A dedicated storage area is provided for tenants to collect and separate office waste.
- The offices were delivered as an integrated fit out.
- Total cost of PVC has been reduced by 30% through the use of PVC alternatives.
- 10% of the contract value is represented by materials or products procured within 50 km of the site.
Land use and ecology
- The topsoil impacted by construction works was protected during construction and then spread over impacted areas to a minimum depth of 200 mm.
- All refrigerants used have an Ozone Depleting Potential of zero.
- Outflows to the sewerage system have been reduced by 50% through the implementation of efficient fixtures.
- The external lighting has been designed to achieve the desired affects without emitting any light beam directly at any point in the sky or across the site boundary.
- Stormwater attenuation ponds were created to reduce stormwater to the predevelopment 1 in 10 and 1 in 50 year flood recurrence flows.
- The 1 in 20 year run-off is effectively retained and filtered for re-use.
“What this project succeeds in demonstrating is that it is possible to ‘go green’ on even the most challenging of large projects,” comments De Villiers.
“It was immensely satisfying to learn that the project achieved a Four (4) Star Certified Rating, proving that teamwork and dedication remain key success factors in the pursuit of environmentally sustainable development.”