Unitised façades - an off-site solution for the building envelope

2010-06-23

Ian Smith from Wicona, looks at the increasing demand for unitised façades, the advantages of this innovative approach to the building envelope, and progress on site at Wicona's largest project to date in the UK.

Ian Smith from Wicona, looks at the increasing demand for unitised façades, the advantages of this innovative approach to the building envelope, and progress on site at Wicona’s largest project to date in the UK.

Whilst unitised façades are still relatively new to the UK, the approach is widely used in Europe and internationally.  This is a purpose-designed solution, based on established façade technology, but using framing sections that are designed specifically for each project.

The Burj in Dubai, for example, is the world’s tallest building – an iconic super tower spanning 189 floors and more than 900m.  And it was constructed using 120,000sqm of unitised curtain walling.

This innovative solution to façade design lends itself well to technically challenging projects, and more complex and bespoke façades.  But it can also be used for fast track schemes, as well as both new build and refurbishment projects – and is ideal where sites are highly constrained.

How the Approach Works

Unitised façades comprise prefabricated units, which are typically the width of a glazing bay and one or two storeys high.  Each panel is fully glazed and sealed off site, allowing the units to be moved to site for fast installation on to pre-prepared fixings to either steel or concrete frames.

The unitised panels can use any combination of profiles, infills, external feature caps and glazing to give building designers complete aesthetic flexibility.  Variations can include stone cladding; metal, composite or polycarbonate panels; windows, doors and fixed light glazing; brise soleil sunshading, and photovoltaics.

What are the Advantages?

So why are more specifiers than ever before now considering a unitised approach to the building envelope?

• Shorter programme times.  Unitised solutions will help contractors and architects meet the increasing demand for shorter programme times, and can achieve impressive reductions in time on site of up to 70 per cent.
• Improved quality control.  Because the façade panels are completed off site, and the external envelope is less affected by inclement weather, quality control is much easier with unitised façades, giving greater peace of mind for the contractor, specifier and developer.
• Aesthetics.  The façade has a huge impact on the marketability of a building – whether it is for commercial office space or apartments for sale.  Both grid and structural glazing are possible with unitised façades, and conventional cladding can be eliminated because the units can hold cladding panels as well as glass.  This gives a single point of responsibility for the façade and means there are no difficult interfaces between different cladding systems.
• Safer work on site.  The units are installed using a platform or hoist, reducing the need for scaffolding and for work at height, which has huge site safety benefits.
• Faster return on investment.  Earlier fitting out is possible on a floor-by-floor basis, as the building envelope on each level is completed – leading to earlier occupation and a faster return on investment for the developer.
• Cost savings.  There are cost savings on site preliminaries and scaffolding, and there is the option of standardisation to achieve economies of scale and material optimisation.
• Reduced storage and handling. The storage of cladding materials and glass handling on site can be completely eliminated – a major advantage for constrained city centre sites and where access is restricted.
• Less wastage.  There is more efficient control of materials in a factory environment compared to a building site that is exposed to the elements and with no protected and secure storage space.  The result is significantly reduced wastage, loss and damage.
• Building movement.  There is no limit on building movement, and the frame sections can be optimised for project-specific loads, such as high wind loadings.

The Cube – A Bespoke Unitised Façade

The Cube in Birmingham is Wicona’s largest project in the UK to date and demonstrates how unitised façades can deliver an architect’s different aesthetic requirements for a single project and a demanding specification, as well as site-related advantages.

The project is the final phase of the highly successful Mailbox development and features 20,000 unitised panels that have now been installed to form a dramatic façade.  With its striking, intricate appearance, the scheme is very different to any other Wicona application – both in the UK and internationally.

Designed by Make, The Cube is a £100m 23-storey mixed-use scheme, which is inspired by the jewellery and engineering heritage of the city, and is based on the concept of a jewellery box.  It is forming a spectacular new ‘entrance’ to the canal network and city centre beyond, accommodating a hotel, waterside retail and restaurants, 244 apartments, offices, rooftop restaurant, and sky bar.

Creating a ‘Jewellery Box’ Appearance

The bespoke façade has been constructed and installed by HAGA using Wicona unitised curtain walling to provide a geometric blend of gold, silver and bronze anodised aluminium panels and glass.  This intricate design is complemented by a decorative metallic fretwork screen.

The 20,000 panels have three different depths, casting a variety of shadows to add texture to the external façade.  The natural silver anodised panels stand out and project from the building, whilst the more subtle palette of light gold was chosen for the mid-panels, and bronze for the units that project the least.

The internal elevations are very different and are more highly glazed, designed to emphasise the jewels within the box.  Glazed unitised panels with frameless windows for ventilation, twist up through a central courtyard and ‘explode’ at the top to crown the building with the city’s first rooftop restaurant.

Site-related Benefits

The unitised façade was engineered to allow a higher degree of movement, and removed the need for scaffolding and material storage on this constrained city centre site.  Its off-site fabrication also allowed each floor to be clad ready for earlier fitting out as the building rose upwards.

The panels were installed using two cranes raised by a hydraulic lift, one of which achieved a full height of over 100m.  Each panel is 1.5m long and is hung internally on an aluminium frame fixed to the building’s concrete structure.  The façade has been designed to have a degree of uniformity across the building envelope, even though the floor-to-ceiling height is reduced for the apartments and the hotel.

This high profile regeneration project also has a low energy design.  The modular cladding gave the architects the flexibility to tailor the glazing on the external and internal elevations in response to potential solar gain, and to provide a high degree of insulation and a low U value façade.

Commenting on the façade design and specification, Frances Gannon, Partner at Make, said, “The Cube is a dramatic building on Birmingham’s skyline, emphasising its status as a world-class city. The specially-designed unitised cladding system has been an important part of the building’s identity and successfully echoes the city’s heavy engineering heritage.  The end result is very beautiful.”

The Cube is due for completion later this year.

What Next?

The biggest challenge for unitised façade specialists is to overcome the resistance to change among many building designers and contractors, and the misconception that unitised solutions have to be more expensive and are only suited to the very largest of schemes.

There has been a lack of innovation in façade design in the UK – but if the aesthetic requirements are balanced with cost, an innovative, bespoke and sustainable design can be produced to a budget.

If all the benefits of unitised solutions are to be realised, façade fabricators will have to take a more manufacturing approach to the building envelope, whilst ensuring they have the production and storage capacity in place that off-site construction demands.