Stainless steel substructures unlock the potential for sustainability

The design and materials used in rainscreen facades can make a real difference to achieving thermal performance targets. Gary Robson, Business Development Manager at EJOT UK, explains why.

Rear ventilated facades, aka rainscreen facades, have become a popular choice for external walling in all types of buildings, both newbuild and refurbishment. This is largely because they enable many of today’s most important design goals to be achieved in a single system, while offering efficient construction of new facades. 

Despite all rear ventilated façade systems being based on the same concept, however, their design and performance capabilities very much depend on what we don’t see once the finished cladding is installed – the substructure. Its significance, however, is often overlooked when the building is being designed.

Decisions around the external cladding panels are often a key focus given the importance of aesthetics and ensuring the building’s appearance is appropriate for the local surroundings – vital for planning consent. But this has to be balanced with the embodied and operational carbon costs associated with the façade and how these affect the building’s overall environmental impact.

Key to this is ensuring the façade substructure allows for obvious thermal targets to be achieved – minimising heat loss and preventing overheating. But the substructure’s contribution to creating a highly sustainability façade does not stop there. 

If a well-conceived stainless steel substructure, like EJOT CROSSFIX, is chosen, rather than the aluminium systems more commonly used, there are additional advantages in terms of minimising material use in the façade overall and delivering a façade aligned to the circular economy. All this while also enabling a higher load capacity and meeting fire performance standards.

Reduced thermal bridging

Key to the improved thermal performance achievable with stainless steel substructures is the ability to reduce thermal bridging. Stainless steel has a far lower thermal conductivity than aluminium which, in the case of the substructure’s bracket and rail assembly, means reduced heat transfer through the façade from the outside to inside and vice versa. CROSSFIX also has an additional advantage thanks to a polyamide thermal stop to further insulate the bracket – known as the Konsole – from the building substrate.

The strength of stainless steel versus aluminium means the number of brackets used to connect the façade panel rails to the building substrate can be reduced. This results in fewer potential thermal bridges being present throughout the façade, meaning there is less opportunity for heat transfer to occur. Such is the effect of CROSSFIX’s ability to limit thermal bridging that the thickness of the insulation in the façade can be reduced without compromising overall performance. And, with less insulation incorporated into the rainscreen system, tangible cost and resource savings can be made.

These factors were among the main reasons why the developer of the Climate Innovation District in Leeds selected CROSSFIX for the highly thermally insulated facades of two large apartment blocks. Here, the design targeted a weighted U Value (based on a typical subframe arrangement) of 0.13W/m²k, with the substructure cavity accommodating insulation with a thickness of 250mm, while maintaining the required ventilation for a system of this type. 

A slimmer façade means more usable internal space

With CROSSFIX, there is also the potential to leverage major commercial advantages in respect of the building layout, given that with a thinner wall build-up – due to the slimmer insulation – the amount of internal floor space can be increased. This enables clients and developers to maximise their return on investment in the site, which is particularly important where the available space for development is limited or land values are extremely high.

Helping to minimise the carbon footprint

Additional advantages come through the stainless steel composition of CROSSFIX, coupled with the efficiency of EJOT’s processes, which mean the system requires significantly less energy during its manufacture than many alternative systems. In addition, the volume of materials required throughout the complete substructure is reduced when using CROSSFIX, particularly in terms of insulation and metal components, thanks to its high strength and low level of thermal transmittance.

This combination of factors means stainless steel can be relied on to be a sustainable choice when planning façade substructures. This is reflected in the CROSSFIX system’s Environmental Product Declarations (EPDs) and Passivhaus certification in Germany. As a result, the system can enable sustainability goals to be achieved in projects designed and built in line with internationally recognised environmental standards such as BREEAM and LEED.

Easy to recycle after a long service life

Considerations about what happens to construction products at the end of their service life have become significantly important in recent years. There is an urgent need to reduce waste and cut volumes of virgin raw materials that are used to manufacture building materials. And, here, stainless steel façade substructures tick all the boxes. 

Stainless steel is 100% recyclable, and it can be recycled indefinitely without loss of quality. This is because its alloying elements remain fully recoverable in the recycling process, which is one of the reasons why stainless steel is also one of the most extensively recycled materials worldwide – a benefit enhanced by the fact that its durability supports circular economy principles.

Compatibility with green facades and living walls

The strength, durability and flexibility offered by CROSSFIX also means it can be used in facades with vertical greening – commonly referred to as living walls or green facades. These have grown in popularity for a wide variety of reasons, such as to encourage biodiversity, provide additional shading and cooling, absorb and reduce noise and help to remove harmful substances from the atmosphere. 

The substructure plays a crucial role in the success of green facades due to the significant additional loads involved from plants, growing media, water retention, wind pressure, and snow (in some climates). It ensures these loads are safely transferred to the building structure, evenly distributed to prevent point failures and resistant to wind suction and dynamic movement. 

Two CROSSFIX projects in Germany demonstrate how effective the system can be for these types of facades. One is a façade at the TEC CENTER of the EJOT Market Unit Construction in Bad Laasphe, designed to compensate for the area taken up by the building and sympathetically integrate within a newly created campus. 

And, in another project, the CROSSFIX substructure was used to create a 600m² façade containing 56,000 plants for an electricity distribution company’s new office building at Moers in the Lower Rhine Valley.

A1 fire performance

Sustainable facades must also be safe, particularly in respect of resistance to fire – and stainless steel substructures offer advantages here. The material has a high melting point (above 1375°C), which means a substructure formed of stainless steel, correctly designed and installed, will remain relatively stable in the event of a fire and maintain its structural integrity. In the case of CROSSFIX, the system also has a Euroclass A1 rating, confirming it does not contribute to fire.

These material characteristics mean that stainless steel could be preferable over aluminium or hybrid façade substructure systems in rainscreen facades, green facades, and buildings with strict fire safety requirements.

www.ejot.co.uk