A building’s façade is what makes it recognisable and stand out from the rest, but in addition to its aesthetic purpose it plays an important role in the energy performance of a building to create a comfortable interior.
In modern buildings, glass, together with aluminium, are very popular for creating spectacular façades with a sense of openness and exterior views. However, glass is not necessarily the most energy-efficient material.
Trend: Shade screens
“One way to achieve the efficiencies required, without getting rid of all the glass, is to add external shade screens,” says Linda Ness, consulting structural engineer at Linda Ness Associates.
“There seems to be a trend towards the design of bespoke external shade screening, driven largely by the current energy requirements. We find that architects are starting to incorporate these into the architecture as definitive features of the building,” she explains. “And as system suppliers start realising the opportunities in this regard, they are starting to extrude bigger fins and bigger areofoils while architects are pushing their limits.”
“ It’s a tightrope walk between beautiful East facing views, very costly glass, and the uncomfortable feeling you get from solar radiation on one cheek and air conditioned cool air on the other!”, she says
Trend: Performance glass
Rui Rodrigues, façade engineering associate at Arup, points out that performance glass technology has also been improving rapidly over the past ten years, with many high-performance solar control glass products available in the market.
These glass products block a portion of the solar energy in the invisible infrared range while allowing more of the visible light to pass through the glass. They can provide a good level of internal daylight while limiting the amount of heat load entering the building through the façade.
Trend: Considering occupants’ experience
Another aspect of façade design highlighted by Rodrigues, besides the managing of solar heat gain entering the building, is a focus on designing for how occupants of the building experience the internal environment.
“Building physics allows the occupants’ experience to be evaluated based on the make-up of the building envelope, such as the location of glass area, glass type, external shading and internal blinds,” he explains. “This approach focuses on the façade and building envelope being defined and driven by the user experience on different elevations and parts of the building.”
Project focus: University of Pretoria (UP) / Cricket SA Centre of Excellence
Ben Kunz, design architect at Neo Dimensions Architects, explains that to create the illusion of the cricket oval extending into the training facility, the building’s south façade is completely constructed out of double-glazed low-E glass with H-column intervals. The Insulvue – 6mm Solar E clear toughened safety glass for the external façade was supplied by Edelweiss Glass and Aluminium.
To achieve the required R-value internally, the north and west façades are made up of Etics, a lightweight composite wall system, while the external façade is clad with a SAGEX product. Jutting from the northern façade is a solar collector box with the silhouette of a cricket player, which generates solar heat to warm up the interior spaces in the winter, which is a substantial energy-saving element.
A custom laser cut, stainless steel, perforated screen was designed as a permanent sun screen on the east façade. The screen projects from the façade with an 800mm air gap to avoid the heat radiation from the screen affecting the thermal behaviour of the building. The structural columns in the façade provided the fixing solution for the sunscreen and solar collector box.
In addition, since the building is orientated slightly west of north, the architects added an exterior solar fin control system that casts shadows over the glass at sunset.
Local vs imported systems?
Rodrigues says that generally, South African contractors use locally designed and manufactured façade systems. “These are either designed and manufactured by the façade contractor or bought from a system supplier in kit form, which is then assembled by the contractor. Many of these systems are well designed and provide reliable performance for façades, particularly in the case of curtain wall façades,” he states.
“We see many local suppliers and contractors developing their own systems,” agrees Ness. “In the past we used many European systems which weren’t necessarily user-friendly in our environment in terms of our building methods and the level of education of our workforce. Some of these systems are very clever and admirable, but there could be unforeseen hurdles such as important parts not arriving and when trying to extrude them locally, the guarantee falls away,” she notes.
“Nowadays, many home-grown systems are designed and produced locally, and are developed by people who understand local conditions,” Ness says.
One area where importing façade systems is beneficial, according to Rodrigues, is doors and sliding door systems. Apart from offering a greater choice, door systems from abroad are designed and tested to tighter air leakage requirements than in South Africa. This is important if energy loss is a concern or to prevent acoustic “break-in”, which can be a problem when noise gets around the seals on the perimeter of the door.
“With any façade system, however, it is vital that the supplier provides support to the façade contractor to ensure that the system is manufactured and installed correctly,” Rodrigues advises. “If an imported system is specified, it is worthwhile investigating upfront what level of support would be provided locally by the system supplier.”
A common problem when engineering façades according to specification, is insufficient information to clearly define the façade and the materials to be used, explains Arup.
“There is a risk that, if the façade is not comprehensively defined at the tender stage, the intent can be compromised in the development of the design by the contactor,” they explain.
A good basis for a specification would be to refer to the Association of Architectural Aluminium Manufacturers of South Africa (AAAMSA) Selection Guide for Glazed Architectural Products.
It is also useful to specify a mock-up of the façade early in the project. This provides an opportunity for the contractor to demonstrate how the façade would be put together, and for the client and architect to inspect and comment on the assembly.
Specifying façades in coastal areas
According to Ness, the two primary aspects to take special cognisance of when specifying façades near the coast are corrosion and wind-loading pressures. “A third could be that there is not such a drastic diurnal temperature range, instead, the climate is slightly moderated at the coast, although more humid,” she adds.
To protect the façade against corrosion, special care should be taken to select appropriate powder coatings for aluminium parts. “We find that professionals who come to the coast from elsewhere are quite unfamiliar with the actual level of corrosion that is experienced here. While they don’t ignore it, they are not always fully aware of the extent of it,” Ness notes.
Secondly, wind pressures at the coast are typically worse than at higher altitudes because the air is denser. This means that the aluminium sections of a façade need to be bigger and not spanning as far as they could inland. The glass also needs to be a bit thicker to resist the stronger wind.
“It is important for architects, clients and developers to involve a façade engineer from the beginning,” advises Ness. “We find that there is still a lot of learning to be done in the industry about the systems that are out there and performance specifications in general, even on quite big buildings, can be very naïve.
“In KwaZulu-Natal there is still an inadequate general understanding of façades and their function. For example, professionals are still putting shopfronts onto the front of buildings in very exposed conditions where they should be using compensated, drained curtain wall systems,” Ness explains.
“We also find that if developers don’t start out with the right advice and only find at the end that the façade design won’t work, they are scrambling to get it right. It certainly isn’t cost-effective or time efficient,” she states.
However, Ness says there is progression in the industry. “AAAMSA has been hugely beneficial in introducing the rating systems and testing requirements that they have. These are forcing people to think and this is having a positive impact.”
Full thanks and acknowledgement are given to Linda Ness Associates, Arup, the SABS and Neo Dimensions Architects for the information given to write this article.