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.

Despite 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 recommendations 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 performance of the building envelope and ease of installation – and the correct type of fasteners 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 managing the thermal differences between the materials being combined, the dead and dynamic loads, plus expansion and contraction of the facade.

Historically rainscreen support components 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 term expectations of their buildings. Taking a complete system approach to rainscreen support provides greater and more readily available technical insight and data, reducing the risk of incorrect specification or product substitution.

Speeding up the specification process through electronic data Having clear visibility on the technical data at the design and specification stage to use in BIM is crucial too and this exists in different forms:

1. BIM structured product data

Structured product data sheets for BIM are available for fasteners which present product information in plain language with simple questions and answers allowing integration into a greater system element, be that data or 3D geometry. They standardise data to enable the comparison and selection of products based on value and life cycle benefits rather than just price.

2. BIM objects

For rainscreen support systems, specifiers can benefit from equally comprehensive information in the form of BIM objects.

These allow for the creation of digital representations of the intended layout together with detailed technical information, accreditations and other background data to provide a relevant information-rich support specification.

3. Bespoke software solutions

Unique software solutions provide project-specific cladding solutions to meet precise requirements. After submitting information online, specifiers receive electronic data such as project-specific bracket and rail spacings, guide pricing per m2 and a prefilled NBS specification document, with an option to access thermal calculations based on the unique wall build-up configuration.

Higher quality fastening systems and new technology to aid the design and specification of the building envelope is a positive step forward. Switching to more advanced solutions often requires small additional capital expenditure, but significant savings in operational expenditure can be achieved.

Andy Stolworthy is director of product and market development at SFS