At 105 Corlett Drive, Birnam in Johannesburg, it’s impossible not to notice the floating concrete and glass office building by Paragon Architects, it’s a site to behold. This two storey office building sits atop a three storey parking podium, separated by double volume metal clad cone forms. The office space is an elongated flattened concrete and glass form enclosed by wrapped ends, which are punctuated with vertical slits, with the east elevation chamfered in plan to follow the site boundary. The conical forms are double volume and include the reception and training spaces. The parking provides for 190 bays. The concept, according to the architects, was derived from a number of sources including the location and context, the choice of materials and the accommodation requirements. The prime site offered an opportunity to generate a jewel box of crafted materials including glass and the Caïman cladding for the cones. The building was meant to challenge the traditional expressions of materials like concrete and glass
The parking podium is constructed from a brickwork and concrete enclosing element with a coated aluminum infill panel. Below this are panels of African Blue Slate Riven Walling as a contrasting ‘band’ to break up the scale of the basement’s bulk. The ground floor podium has winding strips of cold cathode lighting in the soffit which will lead the user to the entrance doors and enhance the playful forms of the cone structures.
The cones are made of a network of steel columns clad in a layer of galvanized sheeting which forms the weather line with the final cladding of the silver CaÏman on a special sub structure made up of ‘omega rails’, which forms a gap between the cladding layers for ventilation. The glazing in the cone forms is a highly reflective glass Solarshield S10 Silver, for the narrow strip windows and dark glass at the entrance shopfronts to accentuate the folding forms of the cones. The roof cones have a lightweight sheet roof on a steel structure with a flat concrete roof over the stairs and lift shafts. The overall effect is a beautiful contrast between the concrete box offices and the silver Calman cladding that give an illusion of a floating concrete box. This effect is enhanced by each cone having a band of lighting at the base and head, so that at night they appear to be detached from the concrete forms above and below. The reception cone has a striking barrisol light inserted in the ceiling bulkhead to create a ‘spaceship-like’ glow. The internal walls of the cones are skimmed and painted dry walling, in sculptural forms which appear to be folding and pull away from the structure in places to make dramatic envelopes of space. The windows are punctured in the walls, with slanted sills and tapered reveals, with an almost Gothic feel.
The concrete box form accommodates two levels of offices and is characterized by its wrapped ends with striking slot windows making vertical ‘slashes’ in the form. The dark glass in the slot windows contrasts with the matt texture of the concrete box. The main glazed façades are single glazed in a slightly reflective glass, in an effort to move away from a very black glass which complies with heating, cooling and glare requirements, but without compromising on performance.
Proper combination of both hard and soft surfaces are seen across the project including polished concrete walkways with a saw-cut pattern and inlays of slate tiles placed at the entrances, in a pattern similar to the riven walling on the basement façade. Beyond this lies the infill landscaping which are xeriscaped using indigenous, low maintenance plants with tall grass-like planting on the perimeter to soften the edge of the building and the balustrades. The roof landscaping matches the ground floor podium with a combination of polished concrete walkways and similar planting.
Although this project was conceived before the Green Star rating tool implementation found traction is not specifically Green Star rated, the building does incorporate some sustainable qualities and challenges the conventional use of concrete and glass in office building.