The new headquarters of the City of Tshwane Metropolitan Municipality, located in the heart of Pretoria, were built with operational performance in mind and is one of the first government buildings to target a 5-Star Green Star SA certification within a public-private partnership (PPP).

Through a PPP agreement with the City of Tshwane, the Tsela Tshweu construction joint venture – comprising Group Five Construction, Trencon Construction and Imbani Construction – was appointed to provide serviced head office accommodation, including the demolition of the old Munitoria building, design and construction of the new building, financing of the project as well as lifecycle capital expenditure management, maintenance and replacements for 25 years.

Paul Silver, executive director of catalytic projects at the City of Tshwane, and Tshwane House project administrator, says: “The intent with this project was to be environmentally responsible by using less water, recycling water, reducing the use of electricity and providing a healthier working environment for the staff through access to natural light and maintaining a comfortable temperature range. The benefit to the city was the development of a building that consolidates dispersed staff at lower costs by reducing the amount of money spent on rentals. Also, through the PPP agreement, the building could be constructed and operated over a 27-year period, with quality controls in place that ensure the services provided by the private party will always be of a high standard.”

Godfrey Place, director of Platospec and project manager on Tshwane House, says the city issued output specifications covering a needs analysis of its accommodation requirements as well as the operational standards to be complied with, including the requirement for a minimum 4-Star Green Star SA certification from the Green Building Council South Africa (GBCSA).

Warren Stanley, director at LYT Architecture, adds that, as part of the RfP bid, the brief gave a very detailed description of performance-based targets that had to be met in terms of design, services and operations. “Through the inclusion of the Green Star criteria, the city ensured a cost-efficient design solution with optimal performance criteria.”

Design

In March 1997, a wing of the old Munitoria building was partially destroyed by fire. The intention with the new building was to consolidate office space for the city’s staff in a building that would provide adequate space for the city’s administrative processes and enhance its service delivery capacity in an environmentally conscious and socially cohesive structure.

Because of the large site, a low building was designed that speaks to the pedestrian scale of the city, with a colonnade providing protection and promoting civic interaction with the building. The elevated ground floor, situated above two basement levels, engages the street on the southern side via a broad staircase and publicly accessible piazza.

Stanley says the fundamental components of the building are a new council chamber, efficient office space, and an environment that provides a pleasant and healthy workplace for staff members. Arrival is through a secure atrium, where the multi-volume space (over five levels) articulates the connection between the two wings of the building and the chamber, thus connecting the various functions of the building while providing a dignified arrival space.

From the central foyer space, there are two bridge links to the east and west wings. The east and west wings are similar in plan, based on a figure-of-eight shape, which encircles two smaller atria. These triple-volume spaces allow daylight into the building without the need for additional facades, thereby facilitating the use of larger floor plates.

The centrally located chamber is a separate structure altogether, with its own formal architecture that makes it recognisable as an iconic object representing the place where city decisions are made. Mirroring the public courtyard on the south is a more private courtyard on the north – a breakaway space onto which the staff canteen opens, which can also be used for functions.

The building’s facades are economical but elegant. Punched windows on the west limit direct sunlight, while curtain walling allows views over the protected courtyards, with vertical shading and canopies to minimise glare.

Sustainable considerations

Although the brief called for a 4-Star Green Star SA certified building, the winning consortium differentiated itself by offering a minimum 5-Star certification.

An independent commissioning agent was appointed to ensure the building is commissioned and operated as intended. Tshwane House received its 5-Star Green Star SA Design rating at the end of 2016, and is hoping to be As-built certified at the end of 2017.

Indoor environmental quality

The building is designed to allow for natural daylight to 93% of the internal space, while at least 70% of the office space has access to external views. Blinds have been fitted to adjust the amount of daylight to workspaces and prevent unwanted glare.

Carbon dioxide (CO2) monitors have been installed to ensure healthy CO2 levels are maintained in the office spaces through the provision of fresh air. To reduce the amount of pollutants indoors, internal finishes with a low volatile organic compound (VOC) content and low 4-Phenyl Cyclohexane (4-PC) were specified.

Energy

The building is targeting a 50% reduction in energy consumption when compared to the energy consumption of a notional SANS 204 building. It has a relatively compact footprint, and the envelope was designed bearing solar, thermal and daylight performance in mind.

The HVAC system is run by energy-efficient air-cooled chillers, serving air-handling units with economy cycles and CO2 sensors, which provide cooling to the spaces through a variable air volume (VAV) system.

The artificial lighting strategy, controlled by the building management system (BMS), uses a combination of daylight sensor-controlled dimmers and efficient fittings, together with occupancy sensors. Energy usage is monitored through a dedicated energy-monitoring system that provides a breakdown of energy consumed and early warnings of unusual consumption.

Heat recovery from the air-conditioning system is used to heat the building’s water, which is produced by five heat pumps that supply hot water at a constant temperature of 58°C.

Water

The building’s reduction in potable water use has been achieved through rainwater harvesting from portions of the roof with a separate pipe system and greywater harvesting from the showers in the cyclist changing facilities. The greywater is used for toilet flushing and irrigation. Water-efficient fittings have been fitted to taps, urinals and toilets. Landscaping with local indigenous plants that require less irrigation also helps to reduce water use.

A separate water-monitoring system, also connected to the BMS, has been installed to determine unusual consumption and detect leaks early.

Waste

The building aims to produce minimal waste from building operations, and the waste recycling area was designed to meet Green Star SA size requirements to cater for future waste handling processes over the building’s lifespan.

Altogether 95% of the building’s steel reinforcing is recycled, and a 65% reduction in standard uses of PVC was achieved through the installation of alternatives such as steel conduits and HDPE pipes.

Highlights and challenges

Stanley says: “It was a great privilege to be able to work on a building that is so visible in the public domain. Tshwane House is synonymous with the identity of city, where decisions about the city will be made, and the future of the city moulded.”

By Karen Eicker

See earthworks magazine issue 38 June-July 2017 for the full feature.