Drawing the curtain wall

Creating a sense of light and space that is both comfortable and practical is one of the biggest challenges in the design of a building’s fenestration package, and the enduring popularity of highly-glazed facades has fuelled the demand for curtain walling systems to perform as well as they look. Andrew Cooper, National Specification Manager from leading aluminium fenestration solutions provider Senior Architectural Systems (SAS), discusses some of the key issues specifiers need to consider.


Frame your vision

When it comes to curtain wall systems, aluminium remains the most popular choice of framing material and a quick look at the metal’s impressive credential explains why. Fully and endlessly recyclable, aluminium is one of the most sustainable building materials available. It is also one of the strongest, and its exceptional durability makes it the ideal choice for projects that not only need a robust solution but also one that can make a positive contribution to reducing future maintenance costs.

In terms of aesthetic appeal, aluminium systems are also hard to beat as the inherent strength of the material allows it to support much larger expanses of glazing within a narrow frame. This offers a sleek finish with slim sightlines and wider views.

The narrow profile of aluminium curtain wall systems is key to achieving the perfect ratio of frame-to-glass that so many specifiers desire, helping to open up a facade and maximise the flow of natural light. The choice of powder-coating options available can also help to further accentuate and protect the aluminium system. From colour-matching to align with a particular brand in the commercial sector, to adhering to planning requirements or creating bespoke designs, the fact that aluminium curtain wall systems can be specified in a wide variety of colours and protective finishes offers almost unlimited design possibilities.

Taking the long view

As well as the aesthetic appeal of aluminium curtain walling, the strength of this type of system can offer practical benefits, particularly for projects that incorporate large spans of glazing in the facade design.

Choosing a system that offers a range of box sizes enables large expanses of glazing to be accommodated, and as these can be reinforced if required for even greater strength, wider spans can be achieved without the need for additional supporting steel to be used. With the cost of steel continuing to rise, the removal of this extra cost – and extra risk – makes aluminium curtain wall systems the perfect choice for such projects.

Choice of configurations

Different capping options for curtain walling systems also play an important role in creating the desired aesthetic, and there is a wide range of configurations to choose from. The use of caps conceals the exterior pressure plates that are used to secure the glass infill panels in place to achieve a more aesthetically pleasing facade. A fully capped system creates the traditional ‘grid’ design, but caps can also be used horizontally along the transoms to help make a building look wider, or vertically along the mullions to give a structure a greater sense of height.

For large glazed facades where a flush finish is preferred, a capless curtain walling system is ideal. Also referred to as silicone sealed, this type of system can create a ‘frameless’ look as there are no face caps to interrupt the exterior view.

Drainage options

Further flexibility is available in terms of drainage solutions, with a choice of mullion and zone drained curtain walling systems. Mullion drained systems are becoming increasingly popular as they can be quicker to install on site and they offer more flexibility for integration with sloped glazing systems.

However, the type of drainage used will depend greatly on the specific requirements of a project and consideration will need to be given to the way the curtain walling integrates with other systems, such as cladding, in terms of the design of the membranes, seals and drainage paths. With this in mind, it’s always advisable to seek advice from the system’s manufacturer prior to work commencing on site.

Thermal performance

Many fenestration systems on today’s market can help achieve ultra-low U-values, but the real test of a product is how it will contribute to the overall thermal performance of a building. For example, careful planning at the design stage is required to ensure that the quest to achieve low U-values doesn’t lead to overheating problems. As it’s more expensive to cool a building using air conditioning than to heat it, it is important that the right balance is found between thermal performance, solar gain and light transmittance. Cold spots and condensation caused by thermal bridging should also be avoided. Again, this is where collaboration with the system’s manufacturer can help, particularly as there is often a considerable difference in the thermal performance requirements of both residential and commercial schemes and it is, therefore, important that system variations can be offered to meet the requirements of either building type.

Putting partnering first

Navigating the extensive choices available can, understandably, be a challenge for specifiers, but through early engagement, architects can tap into the technical expertise of the supply chain to gain valuable assistance with the product selection process as well as access to detailed technical calculations and CAD and BIM drawings. Working ‘one on one’ with a curtain walling supplier provides an effective forum for innovative problem-solving and value-engineering solutions and also offers the reassurance of having all warranties in one place. As the best way to strengthen a supply chain is often to reduce the number of links, streamlining the procurement process is the perfect way to encourage collaboration, fuel innovation and, most importantly, create real value that offers tangible benefits.

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