Cladding’s Class Act
How a new inter-generational campus is setting new trends in rainscreen cladding.
Jedburgh Grammar campus, near to the border town of Kelso, has just opened its doors to a cohort of several hundred pupils. While this is unremarkable for a school of 10,450m2, the fact that students’ ages range from two to 18 is. And that diversity is reflected in the striking design of the building, which was conceived by architects Stallan Brand.
Moreover, the £32m project is also noteworthy as it was delivered on budget and on time, under the management of contractor BAM Construction and development partner Hub South East. Serving as an educational and sporting hub for the local community, Jedburgh Grammar is designed to work with the surrounding topography by partially burrowing games halls into the hillside using large saw-tooth roof lanterns to draw downlight.
The innovative shape, texture and hue of the building is accentuated by the use of lightweight glass reinforced cladding (GRC), which was manufactured by Austrian firm Rieder and supplied ready-to-install by London-based Pura Facades.
James Butler, commercial director of Pura Facades, believes that Jedburgh sets new standards for cladding in the education sector. He said: “Since the dreadful events 2017’s Grenfell fire, we have seen a marked shift in attitudes towards cladding safety and performance. While most schools are under 18m in height – negating their adherence to strict new safety regulations – we are still seeing a general trend towards higher standard, A1 rated materials such as GRC being specified. And this commitment to quality is rarely being ‘value engineered’ out of projects as the build progresses.
“While this concrete material may be more expensive than other options such as aluminium composite (ACM), high pressure laminate (HPL) or even solid coated aluminium we’re seeing more architects on educational projects specify GRC, especially the new generation of thinner, lighter products.”
Jedburgh Grammar uses 13mm Oko Skin cladding from Rieder, which provides a natural stone appearance. Blending well with the rugged landscape of the Borders region, this material is non-combustible and through colour – meaning that scratches and abrasions will not show up on the façade. Thanks to the nature of the material, the cladding will also weather naturally over time in much the same way as stone.
While the A1, non-combustibility of GRC is a given, the long-term performance of the cladding was important given the nature of the building. Hence Pura put the intended Oko Skin panels through various impact tests to confirm its high-performance reputation.
James Butler continues: “Increasingly, we’re seeing architects and specifiers asking for reliable, independent verification of cladding performance, to ensure the chosen material is really fit for purpose. On this occasion we used Vinci’s accredited testing centre at Leighton Buzzard to run the ruler over the cladding. We put the Oko Skin through the ‘soft’ and ‘hard’ body assessments, which examine the structural integrity of the panels using different impact tests.
Increasingly, complete system testing of panels will become the norm,” commented Butler. “These performance measures don’t just look at the inherent properties of the panels themselves, but at the fixing systems that hold them in place. The medicine ball test, as we call it, is especially important in this regard as it provides both architects, contractors and councils with the confidence that the complete façade system will perform over time.”
In the case of Jedburgh’s cladding, this achieved a ‘Class 1 with Negligible Risk’ rating – the best result possible.
Can we fix it?
In all, 2,200m2 of cladding was used on the building envelope. Vitally, the choice of fixing system can often be overlooked, according to James Butler, who makes the point that although it is never seen, the choice of secret or rivet fix is fundamental.
“While a secret fix system was originally planned for Jedburgh, having assessed the cost:benefit it was decided to opt for a traditional riveted, face fixing method instead. While this reduced the cost of fixings, it did create a challenge for Pura and the cladding contractor, who had to work hard to achieve a good colour match. “Stand back a few metres and you can’t see the rivet heads,” said Butler. “This was a great example of achieving a good look within a defined budget.”
Another challenge facing cladding contractors came as a result of the three finishes in which Oko Skin came. “We wanted to achieve a random look to the cladding, using the darkest boards to punctuate the overall design. But achieving randomness is much harder than you think – so we ended up providing the contractor with a design guide to ensure the desired look was achieved.”
Jedburgh Grammar shows that lightweight GRC can create a truly distinctive and durable façade within a budget. Butler comments: “We’re seeing a real trend towards architects specifying new-generation GRC when traditional brick, block or inferior cladding materials would have previously been used. In recent months, we’ve worked with Brighton College, the University of Strathclyde, Ark Soane Academy in West London, The University of Sheffield and Lancaster University to name a few – all using GRC.”
While the material’s incombustibility is no doubt a major pull for risk-adverse developers, the creative possibilities lightweight GRC offers are another reason for the material’s rise in popularity. “Given the wide range of colours and textures now available, we’re seeing more architects opt for GRC, to achieve what was previously done in stone. Thinner, lighter panels of just 13mm also make installation and handling much easier on-site – reducing the possibility of project over-runs.”