The Roof Garden – Cape Town Civic Centre -

The Roof Garden – Cape Town Civic Centre -

The Roof Garden – Cape Town Civic Centre

Project Team

Client. City of Cape Town

Architects. Kruger and Roos

Landscape Designers. Think Ecologic

Botanists. Kirstenbosch Gardens

Irrigation Consultant. Cape Waterplant

Landscapers. Eco Creations Landscapers

Maintenance. Eco Creations in conjunction with Think Ecologic

Due to a shortage of executive space in the early part of 2000, there was an initiative to extend the podium part of the Cape Town Civic Centre to accommodate the city’s councillors and the mayor’s office. This resulted in the building of an additional floor above the existing chambers.

The “sixth floor” project began and the appointed architects, Martin Kruger and Peter Roos, set about designing a masterpiece of glass and aluminium that included a series of courtyards to house the city’s executive team.

Marijke Honig of Think Ecologic, in association with architect Bruce Beyer, were appointed to design the roof gardens and landscapers Eco Creations were appointed to execute this innovative and imaginative concept.

With the open minded approach of the architects and Honig’s passion for “horticultural experiments,” a low maintenance, water wise landscape work of art was created. The project’s landscape design was unique not only because it was the first commercial application of an indigenous gravel garden, but it also featured a water-wise design demonstrating that the City of Cape Town was positioned as a leader in its adherence to water-wise policies. Additionally, many lesser known species of indigenous succulents and bulbs, not previously used in commercial landscaping, were planted.

Design concept

Mayor Helen Zille on the sixth floor of the roof garden. Photo by Bruce Sutherland The primary function of the courtyards was to create a comfortable, inviting outdoor environment where people could relax and enjoy their breaks. Consideration had to be given to shade, seating, greenery, paving and other elements that would soften the environment against the bold geometry of the new building.

The initial mandate for the design of the courtyards was to create outdoor spaces with simple, Zen-like qualities. However during the design process, the team noticed that objects placed in the courtyards looked alienated and lost in the large space and they decided to create a green horizontal plain, a green roof, as opposed to a sparsely potted terrace.

There were also many challenging conditions to consider, namely the strict loading constraints, restricted light, dramatic shifts of the sun and shade which varied from season to season, and the typically erratic Cape wind conditions.

Landscape design concept

Marijke Honig, a landscape designer and botanist with an intense passion for her profession, set about creating seven South African veld-type landscapes and the following concept emerged:

  • courtyard 1 is the Succulent Karoo, featuring succulents, shrubs, trees and bulbs which give a chunky impression of diversity and detail
  • courtyards 2 and 3 represent the Cape fynbos, with restios, aromatic shrubs and seasonal bulbs
  • courtyards 4 to 7 are a variety of Eastern Cape thicket and bushveld plants

The designs involve a combination of decorative gravel circulation areas (which are also used as a water-conserving mulch) to offset the shape and texture of the plants.

Considerations

Load bearing

Measures were put in place to overcome the load bearing constraints and reduce the weight on the slab. Polystyrene slabs were used under the walkways and polystyrene balls were added to the soil to further reduce its mass as a minimal soil layer of only 290mm was imposed. The large trees in the courtyards also posed a problem and the solution was found by positioning them at the intersection of the underlying structural beams.

Soil

The growing medium was critical for the success of these varied botanical gardens. Special soil mixes were specified with adequate drainage and water-retention capacities. Different types of plants have very different soil requirements and as a result, three growing mediums were prescribed, namely fynbos, succulent and general mixes. Another important factor was the transportation of the soil to the sixth floor. The landscapers, Eco Creations, overcame this by using an industrial crane and bucket which was positioned outside each courtyard on the ground.

Irrigation and drainage

The designers were faced with the onerous task of providing an effective solution for the waterproofing as well as the irrigation and drainage.


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