How a collaborative technical approach solved standing seam roof fastening challenge

Jon Knaggs, Technical Manager for Industrial Light Weight Construction at EJOT UK, explains how the company’s testing and development expertise was instrumental in developing the roofing fastener specification for a new glulam-structure civic building in Aberdeenshire. 

As sustainable building designs become more ambitious and combine materials in novel ways, it is crucial for specifiers, contractors and developers to have assurance that the proposed fastener and fixing approach for the building envelope will meet the performance goals. 

The key to developing the optimum fastener specification is early collaboration among the building envelope supply chain partners, from the system manufacturer to the installer, backed by comprehensive testing of not only the fastener but the substrates it is being used with. This is because of the numerous variables which could affect how well the fasteners perform, particularly in roof and façade designs, using materials that are relatively recent entrants to mainstream construction.  

Factors such as greater insulation thicknesses and the need to meet higher performance standards more broadly are also demanding increased scrutiny of fastener choices. There are also location-specific issues to consider, which could influence the corrosion risk and wind and snow loads. 

Meeting the sustainable construction brief 

One recent Scottish construction project highlights how this collaborative approach works successfully. The design of the new £11.4m multi-purpose civic hub in the Aberdeenshire town of Ellon sought to achieve high sustainability standards, which included using a glulam structure, thick insulation throughout the envelope and a Kalzip standing seam metal roof system. 

EJOT UK’s involvement in this project began after we were approached by roofing and cladding products distributor Tektum Supplies, who had been tasked by building envelope contractor Fowler McKenzie to develop a robust fixing specification. The two-storey development features a new family resource centre, library and council offices, with a design to elevated sustainability standards to achieve net zero in operation.  

One of the challenges associated with the construction of the building envelope for Formartine House was to ensure the standing seam system could be securely fixed to the building’s structure. This is formed of glulam beams and supporting secondary steelwork, with the envelope also featuring a thick layer of insulation to ensure the building will meet its sustainability targets and design to Passivhaus standards.  

EJOT’s fasteners are extensively used for Kalzip systems around the world, and this was one of the reasons why Fowler McKenzie was keen to engage with us through our long working relationship with Tektum. It enabled a three-way collaboration to comprehensively support the project team, including main contractor Morrison Construction and the client, Aberdeenshire Council. This provided them with access to a wealth of fastening systems knowledge and testing experience to arrive at a definitive fixing recommendation quickly and reliably. 

Testing the concept 

After reviewing the proposed envelope design, as well as the specification of the substrates and the building structure, we were able to immediately recommend two types of JT3 fastener. One of these, the FM Approved JT3-X2-6.0, is purpose-designed for fixing standing seams and brackets back to steel and aluminium substructures and has been used on projects where Kalzip is specified, as well as other similar systems, for many years. 

The EJOT UK team were initially guided by the fact that these fasteners had already been assessed in Germany as part of resistance testing of the Kalzip standing seam halter bracket to secure National Technical Approval (NTA), which verifies performance outside of the more commonly known ETA (European Technical Assessment). This project was undertaken by EJOT Germany in 2022 via DIBt, a German third-party technical authority in the construction sector. 

Our work involved confirming the performance of our fastening recommendations using the calculations provided by Tektum. Using their own unique prognosis software to generate these calculations, they were able to confirm that our recommendations would satisfy Kalzip’s own technical criteria. The data yield enabled us to conduct a range of detailed tests, including by recreating the application scenarios within our Applitec Centre.  

We started by conducting pullout tests, along with tensile testing in accordance with EN 6892-1 to verify the mechanical characteristics of the steel. This included documenting the ultimate tensile stress and the percentage of elongation (strain), validated against appropriate EN standards to ensure conformity. Furthermore, as the delivered section that we tested was galvanised, the thickness of zinc had to be quantified and subtracted from the overall thickness of the steel section. 

Our Applitec team were also able to look deeper into the material characteristics of the proposed roof build-up, starting with an analysis of the steel section using X-Ray Fluorescence technology – one of several state-of-the-art machines we use. Each of these measurements are used to produce an adjustment coefficient, one adjustment for fabrication and one for material variation, which is used when converting the fractile value into a characteristic value. 

Withdrawal testing, as is typical for such applications, was also undertaken in line with international provisions, in accordance with “Design Assisted by Testing” as set out in EN 1993-1-3 (Eurocode 3). Careful consideration was also given to the glulam sections which were conditioned in one of our Applitec Centre’s dedicated chambers for one week.  

Precise measuring ensured that no violation of edge distances or fastener spacing be incurred when the fastener was subject to axial tension loading, in accordance with EN 1995-1-1 (Eurocode 5). Fixing locations were also inspected for knots, pitch pockets and compression wood in correspondence with relevant EN standards, and the current moisture percentage (CM%) was also determined at each fixing location in order to validate consistency. 

A final test was to look closely at installation (penetration) depth, which was carefully monitored to ensure quality control and consistency. Withdrawal was undertaken, where maximum force occurred at 60 seconds with a specified tolerance, and testing was not complete until full withdrawal of the screw from the timber substrate occurred. 

A partnership approach 

The process adopted here to develop a standing seam fastening specification for the unconventional design of Formartine House is an excellent example of how greater collaboration in the supply chain can pay dividends.  

Our ability to conduct comprehensive testing to internationally recognised provisions and provide the whole project team with reliable test evidence, coupled with the high quality data provided by Tektum from their own calculation software, meant we could assess and analyse the application in great depth at an early stage. This helped to avoid the risk of more costly errors later in the build schedule.  

www.ejot.co.uk