Gary Robson, Business Development Manager at EJOT UK, explains why the design and specification of substructures and the fixing choices are critical to maximising the thermal performance of rainscreen façade systems.
To maximise the thermal insulating capacity of a rear ventilated façade system, the design and specification of the metal substruction used to form it requires careful consideration. Substructures or support frameworks are formed of metal brackets, rails and fasteners attached to the building substrate, providing the frame onto which the outer cladding materials or fascia can be fixed. This also allows a void to be created for the insulation material and a ventilation gap.
However, every bracket holding the frame and outer cladding to the structure breaks the layer of insulation, creating a thermal bridge. While this thermal bridging effect may seem relatively inconsequential, especially where a deep layer of insulation is specified, it can actually be so significant that it undermines the façade’s overall thermal performance.
Unlocking stainless steel’s potential
While aluminium is the most widely used metal for rear ventilated façade substructures, stainless steel can offer significant thermal and structural advantages as the EJOT CROSSFIX system demonstrates.
Stainless steel’s thermal conductivity properties illustrate its superior performance. Aluminium brackets used in façade substructures typically have a thermal conductivity of between 160 and 220 W/mK. In comparison, stainless steel’s conductivity ranges between 15 and 20 W/mK, meaning that it is between ten and fifteen times less conductive than aluminium.
Thermal gains through improved structural performance
CROSSFIX’s stainless steel brackets substantially reduce heat flow through the façade assembly, improving the overall thermal performance of the rainscreen system. This bridging reduction helps to cut heat losses and energy consumption, as well as lower the risk of localised cold spots for building users. But there is an additional benefit resulting from stainless steel’s increased rigidity versus aluminium.
In certain projects, using stainless steel brackets rather than aluminium may allow bracket centres to be wider because of their higher load capacity and stiffness, subject to a full structural calculation. This means fewer stainless steel brackets may be needed across the façade without compromising the substructure’s ability to accommodate the calculated loads.
With a reduction in the number of brackets per square metre, fewer structural connections link between the wall and the outer cladding – lessening the opportunity for thermal bridging in the first place. In addition, the cumulative effect of reducing thermal bridging using CROSSFIX can be so significant that the insulation thickness can be reduced, while still achieving the target U-value.
CROSSFIX is an excellent example of how system innovation can help developers work towards net zero. It also highlights the need to ensure thermal bridging is reduced within the substructure as a fundamental design principle. By addressing heat loss at every bracket and connection point, designers can create façades that not only meet today's performance standards, but are better prepared for the demands of the future.
Find out more about EJOT UK at www.ejot.co.uk/CROSSFIX.
