Driving around in Sandton one can only look out the window to find some interesting and intricate building facade designs on display. By definition a facade is something skin-deep that hides the truth of what lies behind. In the construction industry a facade is the foundation of an aesthetically appealing building, designed to impress the man on the street.
Using mostly lightweight glass and aluminium materials, a curtain wall can be created to display various philosophical concepts like power, transparency, simplicity and style. Recently it has also been associated with energy-efficiency. The design of a facade will all depend on the needs of the client.
Human comfort: material selection and design principles
Neil Macleod, director of Pure Consulting Engineers, says that because curtain walling is an outer covering of a building in which the outer walls are non-structural, the first task when creating a facade is to ensure that the design is weather-tight.
According to him, various elements in the design of a facade should be taken into account to create an environment that is as close to human comfort as possible. “Creating the most comfortable working environment will depend heavily on the selection of the glazing system, solutions to glare issues and temperature control in the building.”
He says the easiest part of a facade engineer’s job is to make sure that the facade structure does not leak, is built on sound and reliable principles and is weather-resistant. “Obtaining human comfort for at least 98% of the inhabitants of the building is where our skills are put to the test.” Facade engineers usually function within a design and construction team to select the right type of materials to construct a facade. This is where elements such as the U-value of the glass system, the cost-effectiveness of a particular curtain walling system and product specification come into play.
Balancing act: comfort vs light
According to Macleod, designing facades is a balancing act, especially when it comes to creating a comfortable office space. “The selection of materials plays an important role in getting enough light into the space, but also managing the glare effect of the glass. One needs to be clever about the design to make sure that all these elements come together in the final design.”
He says the shape, orientation and site that the developers buy will all influence the design of the facade. When clients specify that they want to go green, various other criteria also need to be considered, like the demountability of the system for re-use. “With green design, the use of natural light will increase energy-efficiency – it only needs to be managed so that it does not cause glare issues. The designing of the facade will also have an influence on air-conditioning, as temperature control is central in the designing processes and can be regulated by insulation and glass.”
Facade designs in South Africa
Macleod is of the opinion that in South Africa facade designs are mostly used in commercial applications for corporate clients. “Corporate clients mostly want to make a statement and opt for a more elegant and expensive design that is created with facades.” He says that creating an intricate facade design can be more expensive than building with bricks and concrete. “Corporate clients who are willing to invest more in their buildings will therefore be more likely to use facades than an office park designed for renting out spaces.”
He has hope for facade and glass systems in South Africa as new technologies appear on the market regularly. “Glass products are evolving constantly, creating new opportunities to integrate it into building designs.”
The new R1,6-million Standard Bank office developments in Rosebank that is still in the construction phase, will be able to accommodate 5 600 employees. The additional space will allow for consolidation of occupancies in leased premises in the greater Johannesburg area as well as for growth in staff numbers.
A lot of thought went into orthogonal planning to find the right angles in placing the central part of the building axis at the middle block line. This was complemented by a public piazza that is situated on the northern side of the site. Two large footprint buildings of nine and eleven floors were constructed on the south end of the site that stand east and west of the central multi-volume atrium, extending the flow of the public piazza into the building.
Sculpted U-shape forms modulating the facade were used at the upper levels operating around the subsidiary side atria. The large open space creates a feeling of transparency into the heart of the bank. The volume of the atrium was animated both inside and outside by using vertical circulation via escalators. Multiple pause areas and meeting spaces were combined with a restaurant and meeting centre at the ground level of the building, linking the atrium with the upper levels.
An orientation-responding double facade together with crisp stone cladding accentuate the clean and modern feel of the building to reflect on the corporate philosophy of the bank as an afro-centric organisation.
From the bottom to the top
Pure Consulting was part of the team that constructed the facade system of the building. Macleod says it was Standard Bank’s dream to incorporate a floor-to-ceiling glass system into the building’s design. To achieve this, the ceiling had to be lifted substantially.
According to Macleod, a sloping edge was created by using 450 horizontal glass spandrels to create a visually attractive glass facade. This meant that the daylight could penetrate deep into the building’s office spaces. “The only challenge then was to manage the energy flow of the sun rays to ensure that employees could occupy the building without getting flustered,” says Macleod.
Centralized computer controlled blinds were installed in the cavity between the outer low iron glass and the inside a sealed insulated glazing unit system (SIGU) to regulate the amount of light that would access the offices. The blinds automatically extract or close according to the orientation of the sun during the day. “This is an easy way to control the light levels,” says Macleod. “Light levels were one of the big variables in this project that had to be managed to create an acceptable level of comfort for employees.”
A ventilated double facade design was altered by shrinking the cavity between the facades to create a single system. The single system allowed heat to be trapped in the cavity. “We opted for venting as little as possible of the heat, as the trapped heat could be used for other purposes.” He further explained that insulation was then installed in the cavity to regulate the temperature and absorb some of the heat. The inner-glass used to construct the single-glass facade system had to radiate heat and not become too hot. The heat absorbed by the facade had to be balanced out with air temperature control. “This was done by using air-conditioning facade zones that allowed some of the air to flow in and out of the system.”
To create the outer sheet of glass, high performance crystal-clear low-ion glass was used that absorbs little energy. To create an integrated temperature control system, the glass spandrels were installed using a sealed insulated glazing unit system. Arctic blue soft e-coating glass was applied to regulate the air flowing through the building without stopping it.
The multiple layered glass panes have very dry argon gas between the glass panes. The glass panes are hermetically sealed. Two thick panes of glass are then separated by an air space, within an opening, to improve insulation against heat transfer and/or sound transmission.
The argon gas between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties. Very dry argon gas is a poor conductor of thermal heat, enabling this system to provide excellent thermal insulation.
External shading was avoided by using big modulation units with a protective film that was sprayed on the glass system.
Macleod says that designing and constructing facades is all about deciding what is possible and sensible when using different sizes and cuts of glass modulations units. He says teamwork is at the heart of turning a design into a constructed building. “Without teamwork a facade design such as Standard Bank’s Rosebank offices would not be possible.”
Full acknowledgement and thanks are given to Pure Consulting for the information given to write this article.