Getting rainscreen (bracket) details right

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As rainscreens continue their popularity in both new builds and retrofits, David Fraser of SFS discusses the finer details behind these building envelope systems, and how correct bracket specification simplifies complex challenges

There’s no doubt that rainscreens are becoming ever more popular on both new and old buildings. The rainscreen cladding market is set to continue to increase with the rise in ‘global construction’ (innovation, remodelling, and maintenance) where sustainable cladding and improved building aesthetics are at the top of the list for specifiers and architects.

New cladding solutions and materials are being developed daily, and these building envelope systems are offering architects and developers a wide array of choice in finishes that enable them to explore new design possibilities. However, with more choice can often mean more complexities.

Architects and specifiers face the challenge of ensuring that they specify the correct solutions that not just meet the aesthetic requirements of the project, but are also safe, appropriate to the building application and environment, long lasting, and cost-effective. They must take into account the regulations around thermal performance, ensuring that rainscreens do not lead to poor heat retention and higher energy usage.

A matter of structural integrity

Brackets are integral to holding everything together. Choosing the right bracket for the right application is vital for the building envelope’s durability and safety – and there are numerous options available from differing materials; big to medium to small.

When specifying brackets, specifiers need to consider the structural integrity of the building. This includes looking at the local wind loads, the corrosive substances in the air, and the substrate the brackets are fixing back to.

There are many options when it comes to rainscreen and cladding materials, including zinc, stainless steel, aluminium, natural stone, and fibre cement. It is imperative that the brackets specified can assure the deadweight of the cladding that is being installed on them, as well as being fire-rated.

Balancing these considerations might suggest an endless trawl through production system specifications and datasheets. However, this need not be the case when using tools such as SFS’ Nvelope Project Builder. This online resource can run static calculations completely free of charge and determine the specific requirements of the facades.

It is critical that specifiers know what the bracket is being fixed back to, whether it is to steel, concrete or timber etc., so that the correct primary fix can be specified. For masonry concrete especially, specifiers should also ensure that the correct number of pull-out tests have been completed. If these are not completed, there is a potential risk of issues arising over time.

Satisfying thermal performance needs

As well as looking at structural integrity, specifiers also need to consider the impact the building envelope will have on the thermal performance of the building, in accordance with Part L of the Building Regulations. This helps address energy efficiency requirements in buildings, casting a light on the importance of airtightness and energy efficiency for specifiers and installers.

With building envelopes, it is inevitable that there will be points where heat loss occurs, due to thermal bridging. Thermal bridging happens when there is a thermally conductive connection between the inside and outside of a building. In the case of brackets, thermal bridging can also occur with the fixings used to secure the bracket backs on to the substrate.

Often, the choice is to increase the external layer of insulation to combat this issue and help retain heat in the building. However, this solution isn’t quite so straightforward, as it means that brackets need to be larger to accommodate the thicker layer of insulation, which impacts on the structural integrity of the envelope and costs.

To minimise this thermal bridging effect and to not have to use oversized brackets and thick layers of insulation, specifiers can either look to use alternative bracket materials or use insulated thermal pads attached between the bracket and the fixing structure.

Building a better future

The materials used for brackets, fixtures and fittings are often an overlooked factor at the beginning of a build. It might sound simple, but when looking at designing or redesigning the exteriors of buildings, it really pays to know the environment and the purpose of the building. To minimise misspecification issues before a project begins not only ensures the ongoing safety of the building and its occupants, but reduces costly follow-up maintenance. Therefore, it is vital specifiers bring fastenings, fixings and brackets much higher up the RIBA plan of work.

Newer generations of fasteners, fixings and brackets are being developed by SFS to constantly support more choice, and to aid a quick and easy installation for the buildings of the future.

David Fraser is Nvelope business unit manager at SFS