Small but essential elements of envelope design

Andy Stolworthy of SFS explains why the choice of roofing and cladding fasteners, as well as the rainscreen support system itself, is fundamental to the long term performance of a building envelope


espite being relatively small elements within a project, the choice of fasteners, brackets and rails to secure the building envelope is critical to delivering a high quality, long term result. Original Equipment Manufacturers (OEMs) in the roofing and cladding sector may well be shaping how buildings are designed, built and refurbished, but their innovation is only possible with the right fastening technology. Understanding the interplay between the desired roofing and cladding systems and their attachment to the structure is, therefore, vital in delivering a high level of client satisfaction. Every type of roofing and cladding panel will have recommended fasteners for attaching it to the structure. These recom- mendations will be based on the design of the panel and its aesthetic intention, the type of building structure, the envelope’s thermal and weathertightness properties, and the extent to which the facade will transfer wind loads, impact loads, snow loads and its own self-weight back to the structural framework. With so many factors at play, ensuring that the fasteners are fit for purpose requires ongoing R&D investment by manufacturers and rigorous testing.

Material & colour choices

The primary consideration in fastener specification is the type of metal or other materials used in its manufacture. Austenitic stainless steel fasteners have long been known to offer enhanced resistance to corrosion, compared to coated carbon steel, but many specifiers and clients are now upgrading the specification further by choosing A4 (316 grade) stainless steel – rather than the widely accepted A2 (304 grade).

A4 stainless steel fasteners offer better corrosion resistance and durability, making

them more suitable for more aggressive environments like coastal areas, and they can offer longer warranties. In many applications, the fasteners will require colour matching to deliver on the aesthetic vision. The way the colour is applied, however, will impact on the building’s long term visual appeal, which is why the recommendation for all SFS A4 and A2 fasteners is powder coating. In our experience, the powder coating process delivers a uniform, high quality, decorative and robust finish which is less prone to fading, with excellent weathering resistance and colour stability.

A system approach for rainscreen

All types of rainscreen cladding share the need for a robust and reliable support system to attach panels to the structure. The design of brackets and rails that form these support systems impacts on the perform- ance of the building envelope and ease of installation – and the correct type of fasten- ers must be part of the system, otherwise the whole facade is compromised. Rainscreen support systems are mainly manufactured using aluminium which offers low weight, high strength, excellent corrosion resistance and ease of recycling. Specified correctly, these systems simplify the complexity of a facade and address the multiple technical challenges that current applications present. These include manag- ing the thermal differences between the materials being combined, the dead and dynamic loads, plus expansion and contrac- tion of the facade.

Historically rainscreen support compo- nents and fasteners have been specified and sourced separately. Considering these products in isolation is, however, not consistent with today’s more joined-up thinking – driven by BIM – in which clients expect greater assurances about the long

All types of rainscreen cladding share the need for a robust and reliable support system for fixing panels to the structure



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