The Roof Garden – Cape Town Civic Centre
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.
Mayor Helen Zille on the sixth floor of the roof garden. Photo by Bruce SutherlandThe 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.
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.
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.
The drainage was carried out by laying the screed at an angle that fell into two bores in the corners of the courtyard. A double layer of Derbigum was laid over the screed to ensure that there was no water leakage. In addition, another waterproofing product, consisting of egg-shaped hollows which regulated the flow of the water, was also used. Over this, a layer of geotextile was placed to filter the water from the soil on the surface. The correct soil mix came into play here again, as it needed to drain adequately, ensuring that the water would flow freely towards the open bores.
Thus, the method of irrigation was a critical component to the drainage. Drip irrigation was selected as it was the most effective watering system and is 50% to 70% more efficient than conventional spraying irrigation. Drip irrigation runs on a low-pressure water system and the pipes with tiny holes were placed on top of the soil surface and covered with a decorative layer of gravel. An irrigation consultant designed the drip system as this method is conventionally used in agriculture and not landscaping.
Utmost care and consideration was taken when selecting the individual species for the chosen garden themes. Eco Creations carefully selected a team to ensure that the design and concept were adhered to at all times. The design specifications relating to the placement of the plants resembled a high tech military procedure and supervision during planting was critical to the plants’ future well-being. So intricate was the design and dedication of the designer that every minute, clearly thought-out detail was strictly adhered to. Plants were precisely arranged, with the emphasis on texture, shape, size and their relationship to one another. This dedication and attention to detail have brought out the beauty of these natural indigenous roof top gardens.
Although maintenance is often the factor that is neglected by developers and architects, this was not the case with this project. As with the rest of the project, it was carefully planned to continue for a full 18 months after completion. Great care was taken to ensure that feeding, irrigation and plant care was maintained. Trees were fertilised, beds were weeded, flowering plants were pruned, groundcovers trimmed and soil tested and replenished. Today the gardens are maintained by Eco Creations and overseen by Think Ecologic. The city’s councillor manager, James van As, is to be commended for acknowledging the need for specialised care for this public “work of art”.
Text by Beth McKellar-Basset. Photos by Marijke Honig