Curtain wall systems enjoy wide appeal across a vast range of structures, offering the designer and client a sleek, high-performance building envelope, enhancing both aesthetics and functionality. Curtain walling provides extremely flexible options for external envelope enclosure. Different curtain wall types each offer their own advantages, emphasising the importance of correct specification for the application in question. This article is intended to help you gain a deeper understanding of what factors to consider as you close in on the right choice for your own curtain wall project.
Curtain walls are non-load-bearing exterior walls made from lightweight materials including glass and aluminium. In contrast with traditional walls, they will not support structural building loads, thus offering greater architectural design freedom than many other solutions.
Key benefits of curtain wall systems include:
Aesthetics – A transparent and modern high-tech exterior envelope.
Natural light – Curtain walls provide excellent levels of natural light in the building, providing important health benefits.
Thermal efficiency – Ample opportunities to effectively insulate the building interior without compromise to envelope transparency.
Weather resistance – Curtain wall facades afford a highly effective, airtight barrier against the elements.
Coping with structural movement – Glass curtain walls can be engineered to accommodate building expansion and sway.
Curtain walling has been very successfully integrated into an exceptionally wide range of projects and different types of curtain wall system have evolved to provide tailored solutions.
Here’s a brief analysis of the most common types of curtain walling.
The most established and traditional method of curtain wall construction. Stick-built systems are manually assembled piece-by-piece on-site. Mullions (vertical elements) and transoms (horizontal elements) are installed first, followed by glazing panels.
Stick-built curtain walls offer the widest possible project customisation and adaptability and are the ideal solution when a project potentially requires component adjustability during installation, allowing for any last minute on-site design changes.
Designers enjoy optimal technical and aesthetic flexibility with stick-built systems, thanks to a huge range of shapes, sizes, infills and additional elements.
Low to mid-rise buildings are particularly suited to stick-built solutions, which are the curtain wall system of choice when cost-efficiency is paramount.
Kawneer’s stick-built curtain wall systems include the AA®100 50mm Curtain Wall System and the AA®110 65mm Curtain Wall System.
Application example – Kawneer stick-built curtain walling accommodated a 9.5mm triple-laminated glass fin detail for solar shading on an impressive curved frontage at Stafford College Skills & Innovation Centre.
A unitised curtain wall is a modular method of construction. Each panel is a self-contained module (usually one floor tall and one bay wide), integrating glazing, insulation, and aluminium framing.
Unitised systems are pre-assembled in factory-controlled environments into large panels, then shipped and installed on-site.
High-rise, multiple-storey structures are the perfect application for a unitised system, particularly when site access is limited and the best installation solution is to crane-in curtain wall modules. Weather dependency is also reduced, enabling the construction programme to continue when it might otherwise be delayed. These practical advantages will often more than offset the initially higher cost of unitised systems.
The repetition and scalability of uniform modular panels affords the designer a high-tech building aesthetic, further enhanced by factory quality controls that ensure unitised modules achieve high-precision alignment on site and a totally consistent and reliable finish and performance.
Buildings with higher levels of building movement and heavier infills also greatly benefit from unitised systems, which have capacity to cope with these key project demands.
Kawneer’s unitised curtain wall solutions consist of the AA®201 Unitised Curtain Wall and the AA®265 Unitised Curtain Wall.
Application example – Kawneer unitised curtain walling was used for a world-class medical facility in Manchester.
Whether you choose a stick-built or unitised curtain wall, there are some key glass fixing options to consider:
Structurally Silicone Glazed (SSG)
Here glass is bonded to the frame using structural silicone, eliminating the need for exterior metal caps and providing a continuous sleek and high-tech glass façade.
Designers looking for a seamless and uninterrupted glazed curtain wall appearance will often favour an SSG system over other options, as it offers the ultimate curtain walling aesthetic, most notably for high-rise applications.
SSG systems are also very popular on projects where thermal efficiency is a prerequisite, due to their superior thermal-breaking and tight sealing.
Kawneer dedicated SSG curtain wall systems are AA®100 Structurally Silicone Glazed (SSG) and AA®110 Structurally Silicone Glazed (SSG).
Application example – A Kawneer SSG solution was used on a stunning glazed facade at Birmingham Symphony Hall.
Capped
Capped curtain walling uses pressure plates with cover caps to hold glazing in place.
Designers looking for a more traditional low-rise curtain wall grid appearance will find that capped systems provide an ideal solution with tremendous flexibility in terms of colour and finish options. They are also the best option for tight budgets.
Building owners will derive long-term benefits from the relatively simple maintenance regime for capped curtain walls, including easy glazing replacement when needed.
Capped curtain walling can be a more suitable option than SSG, when high levels of building movement are inherent in the design (a bespoke Kawneer capped curtain wall solution was used to cope with +/- 12mm concrete floor slab deflection).
Typical Kawneer capped curtain wall systems include the AA®100 HI Curtain Wall System.
Application example – Kawneer capped curtain walling helped in the creation of one of the world’s largest Passive House certified leisure centres in Staines-upon-Thames.
Concealed Vent
A concealed vent curtain wall system maintains an uninterrupted curtain wall appearance, while integrating operable vents or windows that have been engineered to blend seamlessly with the fixed glazing.
Concealed vent is the perfect option when natural ventilation is required, whilst maintaining aesthetics with no visible framing.
A motorised option offers the ultimate ease in operation. However manually-operated venting can facilitate a concealed vent solution in more cost-conscious settings.
Kawneer offers two dedicated concealed vent curtain wall systems.
Application example – A motorised Kawneer concealed vent system was used in the creation of a stunning curtain wall façade at Anna Freud Centre, London.
Fire Resistant Curtain Wall System
These systems provide increased safety and compliance with regulations, designed to slow the spread of fire. They are also able to incorporate automatic smoke vents and panic opening doors to assist with the safe evacuation of occupants.
Blast Enhanced Curtain Wall System
A blast enhanced system mitigates blast loads created by accidental or intentional explosions. It is designed to minimise structural damage to the building, providing a ‘shield’ in contrast to a conventional ‘envelope’.
System choice is highly dependent on a very project-specific blend of requirements. However, the following considerations are universal to any building:
1. Building Height and Loads
Unitised systems’ enhanced ability to deal with wind loads and building movement make them very suitable for high-rise projects. In contrast, low-rise buildings benefit from the lower costs and site/construction flexibility of stick-built systems.
2. Climate and Weather Conditions
SSG systems potentially offer the most optimal weather sealing capabilities. However, other options can be carefully designed and constructed to offer comparable performance.
3. Aesthetics
SSG systems are ideal for uninterrupted high-tech glass façades. Capped systems with visible mullions offer a more traditional framed appearance.
4. Budget and Schedule
Stick-built curtain walls are more affordable, but are relatively slow to install, in contrast to unitised systems which offer very worthwhile construction time savings, especially on taller structures, but which cost more upfront.
5. Maintenance
Capped systems typically afford simpler glass replacement than bonded SSG curtain wall units. They do require higher levels of ongoing maintenance, however.
Whatever system you decide on for your glazed curtain wall project, aluminium offers a unique combination of sustainability, performance and aesthetics.
• Sustainable
• Design flexibility
• High strength-to-weight ratio
• Durability and resilience
• Huge range of flash options
• Occupant comfort
• Easy maintenance
Kawneer has created a comprehensive online guide to the use of aluminium in building and construction
Selecting the right curtain walling system is ultimately a balance between practical and aesthetic considerations. No two projects are exactly the same, but curtain walling is sufficiently versatile to offer an ideal solution for almost any conceivable application.
We hope that this overview has helped you to focus on some of the key solutions for your current project.
For more specific advice, our Architectural Advisor Team members are ready to assist you, offering a wealth of experience.