How to maintain performance from design to site

Guidance on complying with Building Regulations is becoming more complex. The Building Safety Act is introducing ‘Gateways’ for high-risk buildings to ensure specification integrity is maintained from design through to build. So, what factors help to translate designed performance into as-built performance?

Last summer saw an uplift to England’s Approved Document L (Conservation of fuel and power), which introduced tighter limiting U-values for new elements to encourage better thermal performance. 

However, turning specified U-values into as-built performance requires calculations to be as accurate as possible. Simplified calculations aren’t suited to rainscreen facade systems because they apply a blanket correction factor to account for things such as penetrations from the steel frame, which can result in inaccurate specification.

Why 3D U-value calculations matter

A better approach is to insist on 3D U-value calculations from the manufacturer. These attempt to more accurately account for the impact of those penetrations, making them a better indication of as-built performance.

In addition, architects should request an in-depth report detailing what components were included in the calculation. This will ensure the supply chain can see how it was calculated and therefore how changes to the specification could affect it, helping to protect the design.

Uncompromised installation

To deliver its specified thermal and fire safety performance, insulation must be correctly installed with minimal gaps. Traditionally, cavity barriers present a challenge to this because they require the insulation to be cut post-installation; a time-consuming process that can result in unintentional air gaps.

Knauf Insulation has addressed that challenge with product innovation. Last year the business launched Rocksilk RainScreen FFCB, the only cavity barrier that can be fixed to the face of the sheathing insulation in masonry facades.

It is part of a certified system comprising Rocksilk RainScreen Slab sheathing insulation for behind masonry facades and fixings. It is quicker and easier to fit correctly and, because the insulation doesn’t need to be cut post-installation, it reduces the risk of gaps that could compromise performance.

Non-combustibility

Passive fire safety measures such as insulation rely on complex system interactions or third-party elements to perform correctly and any deviation from the design specification can prevent them from living up to their fire-safety credentials. Using combustible materials creates an additional level of risk.

The importance of non-combustibility has been reflected in updates to Approved Document B (Fire safety) for England, which already required non-combustible materials to be used in all relevant buildings above 18 metres.

Following the updates, products with Euroclass A1 or A2-s1,d0 reaction to fire classification must also be used in certain external wall system build-ups, such as rainscreen facades, on all residential buildings between 11 and 18 metres. The only exception is where a full-scale fire test to BS 8414-1 or BS 8414-2 has been undertaken.

Products such as Rocksilk RainScreen FFCB and Rocksilk RainScreen Slab, which are non-combustible with Euroclass A1 reaction to fire classification, offer performance alongside greater peace of mind.

Achieving real-world thermal and fire safety performance in rainscreen facade systems requires continuity from design through to completion.

That means prioritising accurate calculations, along with non-combustible products that are easier to install correctly. By taking these factors into account, architects can help to create buildings that live up to their designed performance.

Learn more about Knauf Insulation's rainscreen facade systems and how to request a free 3D U-value calculation.

For more information and technical support, visit knaufinsulation.co.uk

Contact:
technical.uk@knaufinsulation.com

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