Correctly designed, specified and installed, rainscreen façade systems can give a sustainable new life to an existing building and secure their future within a low carbon built environment. However, the effectiveness and suitability of these façade types in refurbishment projects is heavily dependent on the performance and structural integrity of the substructure.
Despite being hidden from view once complete, the substructure makes a significant contribution. In many cases, the focus at the outset is on the appearance and durability of the outer cladding, given how important these are aesthetically and to meet planning requirements. As a result, the substructure’s performance and specification risks becoming a lower priority in early design stages.
Giving the substructure equal attention and focus early, however, is increasingly necessary as expectations for the façade’s performance in refurbishment projects grow ever more demanding. Whether you are considering a complete system from a single supplier, such as EJOT CROSSFIX, or a substructure using components from multiple manufacturers, taking time to evaluate how well the finished system will perform will pay dividends.
BALANCING THERMAL PERFORMANCE WITH FIRE SAFETY
Rear ventilated facades allow for deep layers of insulation to be applied to the original building, offering immediate thermal upgrade potential in refurbishments. But this is not the only thermal consideration – the insulation’s performance can be significantly undermined by thermal bridging. While aluminium brackets and rails have traditionally been favoured, this type of metal conducts heat far more readily than stainless steel. That means greater potential for heat loss through the façade when using an aluminium framing system, undermining the building’s overall energy efficiency goals.
When the cumulative effect of hundreds of brackets across a façade is considered, the thermal bridging effect using aluminium can be substantial. Switching to stainless steel can cut heat loss so significantly that it may be possible to reduce the thickness of the insulation used in the façade or achieve an even lower overall U-value without increasing the depth.
The insulation’s thermal performance must, of course, be balanced with the need to minimise fire risk. In addition, open or closed state cavity fire barriers may need to be integrated to prevent fire spreading. To ensure cavity barriers are installed in line with manufacturer recommendations and the building’s life expectancy, it is vital to choose either a bi-metallic, A2 or A4 stainless steel fastener, all of which are offered by EJOT.
Choosing a stainless steel substructure like EJOT CROSSFIX also helps to support enhanced fire safety objectives because the metal retains a higher degree of mechanical strength at high temperatures compared to aluminium. This is why the CROSSFIX system is classified with an A1 fire rating according to EN 13501-1.
MULTIPLE SUBSTRATES
Given the huge variation of construction styles in many older buildings, particularly those that have been extended, façade substructures in refurbishment projects must often work across numerous substrates. The EJOT range can facilitate this, spanning everything from the backing structure framing, profiles, brackets, fasteners and fixings, all supported by substantial test data with many also independently certified with European Technical Assessments (ETAs).
STRUCTURAL INTEGRITY AND MOVEMENT
Rear ventilated façades rely on a substructure capable of withstanding various loads throughout their lifetime. As well as the dead load (self-weight) of the façade system itself, the substructure must also accommodate negative and positive wind loads, which push and pull the façade, as well as impact loads and potentially other types of loads such as those resulting from seismic activities. The most appropriate anchoring method for the backing structure, profiles and brackets will depend on the substrate materials and calculated loads – all of which are covered by the EJOT range. A concrete structure could require a masonry anchor, concrete screw, screw and sleeve combination, through-bolt or resin fixing, for example, whereas attaching a sheathing board to a steel frame building may need a carbon steel self-drilling wing fastener.
If a complete subframe system is specified such as CROSSFIX, which can be used with constructions as diverse as light gauge steel framing and traditional brickwork, it may be easier to confirm its ability to accommodate the calculated loads given the test evidence provided in the supporting ETA. Where a complete system is not the preferred route, the suitability of each component needs to be assessed to ensure they will all meet the load demands.
As the façade must also be designed to move as a result of temperature changes, careful consideration has to be given to the mix of fixed and sliding points in the framing to prevent a restriction in movement where it is needed. Innovation in fastener design is also helping here, particularly in respect of sliding point screws where smooth, controlled movement is essential. The EJOT Vario
screw is designed for use in both fixed and sliding points, with a buffer zone between the screw head and sliding washer. It will clamp securely in fixed points while allowing consistently low contact pressure in sliding points.
OVERCOMING WIDER CHALLENGES
Well-conceived substructure components and systems can also help to streamline the delivery of façade projects, offering efficiency gains at multiple points in the supply chain. This can reduce errors and avoid the administrative burdens that often hinder refurbishment projects. For example, the EJOT Konsole bracket – a key component in the CROSSFIX system – is designed to be used with both horizontal and vertical rails, meaning there is no need for two different products where the façade requires both rail orientations. This reduces the risk of the wrong brackets being used on site and simplifies the ordering, stockholding and stock management processes. www.ejot.co.uk