One of the main complexities in designing a glazed façade is the accommodation of slab movement/deflection. Due to the extension of structural spans seen in contemporary building designs, slab deflection is increasing. This places additional demands on a façade design team to accommodate movement between slabs and façades.
When building designs require glazed facades to withstand high slab deflections, one solution is to incorporate unitised curtain wall systems like Kawneer’s AA201 or AA265 systems, which, due to their construction, can provide greater movement allowance. However, unitised curtain walling usually comes at a cost premium, and is generally more appropriate for very large facades, and where there might be issues of site access. Traditional stick curtain wall is more readily used by most fabricators and installers in the UK, hence the development of a new expansion joint by Kawneer.
This new development has enabled Kawneer to offer an expansion joint for its AA110 SSG system that can withstand a +/- 5mm amount of movement tolerance. The recent launch of the capped variation of the expansion joint for Kawneer’s AA110 curtain wall system, which allows a +/- 15mm building tolerance, has been successfully followed by the structurally silicone sealed (SSG) variant.
While a conventional SSG system is limited in its movement capabilities due to the hidden clamping nature of the glass and toggle engagement requirements, the new Kawneer solution has redesigned glass clamping rails and a redesigned toggle system, to allow for greater slab deflection and differential movement. The addition of the SSG expansion joint allows increased flexibility in architectural specification, where the clean lines of a silicone-glazed façade are desired, but without compromising the requirement for reduced slab sizes and cost.
The new joint locates at each slab level and is therefore concealed by spandrel glass or panels. Its specialised engineered foam seals expand and contract with the movement of the structure.
To ensure compliance with UK standards, the new enhancement has been rigorously tested during development to ensure high performance in all UK conditions. In consultation with the Centre for Window and Cladding Technology, an enhanced version of the ‘Standard for Systemised Building Envelope: Sequence B’ programme was developed. This included a series of performance tests while the new +/- 5mm SSG expansion joint was in its compression, extension and neutral positions.
Alongside the new expansion joint enhancement, Kawneer has also increased the glazing weight capacity of the AA110 system, which will bring it in line with the current AA100 system, providing glass weight capability of up to 600kg. The introduction of a 36mm thermal break provides enhanced thermal performance and increased glass thickness capability up to 50mm.
Gary Ledger, Kawneer’s technical director, said: “Glazing and cladding systems need to be designed to allow for building movement without compromising the performance or safety of the system. The consequences of failing to provide enough allowance for in-service building movement can range from a reduction in weather performance to glass breakage and significant system failure.
“Our new +/- 5mm SSG expansion joint is a welcome addition to our AA110 product offer, and follows on from the popular capped expansion joint launched in 2019. This subsequently gives architects ultimate design freedom by providing a traditional stick curtain wall system that gives exceptional performance and tolerance of building movement.”
