Gordon Hines

is the UK Technical Manager for SFS Group Fastening Technology

Securing rainscreen systems for longevity and structural integrity

As a highly-experienced specialist in the creation and development of rainscreen cladding support systems, as well as carbon and stainless-steel fastening solutions, SFS Group enjoys excellent working relationships with many of the industry’s major panel manufacturers, as well as leading installation specialists and architectural practices. As a consequence, the company has had a pioneering role in the development of the new-generation fixing solutions that have facilitated the trend towards the construction of taller buildings, accordingly dealing with progressively more challenging loading conditions.

The company’s UK Technical Manager, Gordon Hines, explains: “Rainscreen systems are nowadays being used in situations where they would not previously have been considered; morphing from a solution to overclad two- and three-storey structures to a situation where they are now regularly specified on very tall buildings, up to 30 storeys high, where they are subject to much greater wind and other load conditions.

“Therefore, they need to be very robust to achieve the longevity – the performance and the appearance that property owners and occupiers demand – and that requires proper analysis of the conditions, sub structure and the nature of the cladding panel in order to achieve the right solution.”

SFS Group Fastening Technology’s support for specifiers extends from delivering multiple RIBA-certified CPD seminars to its SFS ConnectSuite online tools and the highly-experienced technicians in Gordon’s team, who undertake hundreds of pull-out tests for clients every year to determine the strength and suitability of walls as well as roof decks.

Gordon continues: “Whether fastening into steel or timber studs or some type of masonry, the fixings need to be covered by an ETA providing the independently-tested values. However, with masonry or concrete, although there might be ETAs available, it is generally regarded as good practice to conduct a pull-out test on site to verify the substrate. It also needs to be noted that all fixings within a rainscreen system are not operating in a fully dry environment, so they need to be of the appropriate quality depending on the material used in the subframe. As most are fabricated from aluminium, then the fixings ought to be A4 stainless steel to ensure the best long-term performance.

“Then, as the work of the subframe is unseen, the fixings from that to the panels are often overlooked. It is important for fixings to be approved by the panel manufacturer – or OEM – as being suitable, while the fixing suppliers should conduct widespread testing to ensure everything is fit for purpose. Each panel type has its own limitations and these, together, with the allowance for movement, need to be factored into the way these are attached to the subframe.”

Accommodating movement is key

While the need to allow for structural deflection and thermal movement is implicit in UK design codes, for rainscreen cladding, it is crucial to understand where the fixed points are, and also the positions where sliding movement can best be accommodated, if serious problems are to be avoided in hot weather. Decorative cladding panels can be subject to buckling or can actually snap if the design and calculations are wrong.

Gordon recounts: “What we have been finding lately is not related to the actual retention of fixings within the structure of the wall but with movement across the subframe of various rainscreen systems. As a result, we are regularly being asked to investigate facades that have had to be stripped back, and clients often don’t realise that we need full access in terms of scaffold or hydraulic platforms in order to carry out tests at multiple locations across a building’s elevations in order to get a clear picture of what is occurring. Then, we can advise the client or designer with our recommendations on remedial works to ensure an installation does not encounter similar issues in the future. Our preference generally is to establish the fixed point for a rainscreen system in the middle of a wall and allow thermal movement to take place at either end, which is good practice and actually reduces the amplitude of movement. "

Finally, Gordon turned his attention to the potential pitfalls associated with the secret fixing of panels. He concludes: “Fibre cement panels are very popular at the moment and can be face or secret fixed. Secret fixing, which features TUF-S-type fixings, requires a lot of testing, as the further into the panel a fixing is embedded, the better the test results. Unfortunately, though, this also increases the chance of ghosting of the panel fixings, showing their position on the face as the panel dries after being rained on. Some manufacturers do a lot of expansion testing as well to prevent cracking of the facade. Then, with face fixing, the head size, pull through and allowance for expansion all need to be factored into the choice of fixing type. After all this testing and work, it is vital that the panels are fixed to each manufacturer’s recommendations.”