The ONYX Building, designed by Robert Silke, stands as one of Cape Town's modern architectural icons. Our client acquired a penthouse within this landmark and commissioned us to create a rooftop garden. Her brief was clear: she wanted a fully realistic garden — something that felt like a natural, ground-level space rather than a typical rooftop installation.
The project presented several significant challenges. The rooftop was finished with decking, leaving only a 40 mm void to the structural roof — far from ideal for establishing planting depth. In addition, the site is exposed to strong winds and offshore salt mist due to its proximity to the harbour. Logistically, transporting materials to the rooftop and completing the project within a strict two-month timeline added further complexity.
Despite these constraints, the site offered a major advantage: uninterrupted, sweeping views of Table Mountain. We used this as a central design driver.
To enhance both space and experience, we incorporated curved mirrors throughout the garden. These not only reflected the mountain from multiple vantage points but also visually doubled the perceived size of the space, creating a sense of expansiveness. The mirrors were carefully shaped to complement the architectural language of the building and detailed with black lining elements that echo Silke's original design features.
Planting required a highly considered approach. We cut and shaped planters directly into the deck, lining them with waterproof membranes and geotextile fabric to protect the structure. Plants were installed in fabric grow bags to prevent root damage while still allowing healthy growth. To introduce vertical interest and a sense of maturity, we added raised planter boxes in key corner areas, finished to match the existing decking.
Given the harsh coastal conditions, we selected hardy, endemic plant species capable of withstanding wind and salt exposure while maintaining a lush, natural aesthetic. The garden was completed with integrated lighting, an irrigation system, and a water feature to enhance ambiance and usability.
The result is a rooftop garden that defies its constraints — an immersive, grounded landscape that feels entirely at home, despite its elevated setting. Truly, a one-in-a-million project.
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